Tomos CDI Ignition

August 13, 2008

Table of Contents

Ignition ……………………………………………………     1

How to test a coil…………………………………….    1

How to check for spark……………………………    1

Ground the coil wire to stop the spark…..    2

Tomos A35 and A55 CDI ignitions…….……..    2

Ignition timing…………………………………………   2

Ignition symptoms………………………………….   3

Ignition

The ignition is like the electric pulses of a heart beat. The voltage pulses are in sync with the rotating crankshaft. When the crankshaft rotates faster (or slower), the spikes are closer together (or farther apart) in time. See figure 5.

Figure 5: Ignition is neither AC nor DC, but instead a train of narrow pulses, each happening at a precise time.

What makes the gasoline ignite is the spark plug sparking, in the right way, at the right time. What makes the spark jump the gap of the spark plug is a sudden very steep rise in voltage, to over 10,000 volts in under a few thousandths of a second. What makes that high voltage spike is a transformer, usually called “the ignition coil”. A transformer is like a car jack. It steps up (or steps down) voltage while stepping down (or stepping up) current. A sudden change in current in the (thicker but fewer) primary windings induces a sudden large change in voltage in the (thinner but many more) secondary windings. Supplying the transformer with a sudden change in current is either a CDI unit (Capacitor Discharge Ignition), on 1994 and later, or a mechanical points and condenser, on 1993 and earlier models. On late model Tomos mopeds with CDI ignition, the electronics are molded into the coil (unlike most Asian types). The “control unit” or “CDI unit” is a small 1.5 inch square circuit board, hidden inside the black plastic of the coil. Early models before 1994 had plain coils, without any electronics.

How to test a coil

Any ignition coil (coil only, not coil-with-CDI like Tomos uses) will produce a spark on a spark plug, at the instant the input wire is touched to a 12 volt battery (+), with the battery (-), coil, and plug all grounded (with clip leads). If you touch it slowly to the battery post, it will produce a weak spark. If you swipe the coil wire fast and hard against the battery post, it will produce a strong spark. This demonstrates that it’s the shorter “rise time”, much faster than the blink of an eye, that makes a better spark. Only perform the above spark test on plain coils. CDI/coils might get damaged from the high current possible. Never connect a 12V battery to a coil for longer than one second. It turns out that moped coils are never bad. Only occasionally the CDI/coils go bad. “Bad” means it produces no spark at all, or it produces weak or intermittent spark. Intermittent spark is like turning a light switch off and on, often in an unpredictable way. The only way to test a CDI/Coil is to put it on a known good running bike and test ride it, listening and feeling for any stumbling or misfiring. If no test bike is available, then the only way to test the CDI/Coil is to replace it with a known good one, and hope that fixes the problem. If it’s not the CDI/Coil, and not the bike’s wiring, then it must be the magneto. The CDI magneto costs way more than the CDI/Coil, and is more difficult to change, and so it’s last.

How to check for spark

CDI solid state ignitions have shorter rise and fall times than mechanical point ignitions. That makes them start with a weaker kick, or even with your hand. CDI ignitions have a faint spark that is sometimes invisible in bright sun. Always check for spark in the shade. “Checking for spark” means removing the spark plug, connecting the plug wire to it, laying it on the engine so that it’s metal shell is touching ground (the head fins), and then turning the engine over (by pedaling backward or kick starting) while watching the gap between the electrodes of the spark plug. Spark color indicates temperature. Blue spark is hotter than pink or yellow. Faint blue spark is good. Bright white spark is bad, usually because of a semi-conductor-coated “fouled” spark plug.  The white porcelain insulator must not be coated with black or shiny carbon. If it is not dull white, tan, or brown, then use a new spark plug to check for spark. A fouled plug will spark badly or not at all, even when the ignition is working fine. You can also hear the snap sound of the spark. Loud is good.

Grounding the coil wire stops the engine 

In both CDI and points type magneto ignitions, the “heart beat” is intentionally stopped when you turn the engine stop switch off. When the “kill” switch is “on” the ignition wire is not grounded. When the kill switch (engine stop) is “off” the ignition wire is grounded. This is the opposite of a (battery ignition) car. So to hot wire a magneto ignition bike you only need to disconnect or cut the kill switch wire so that it cannot be grounded. When troubleshooting a late model Tomos that has bad or no spark, the way to eliminate all the wires in the bike is to plug the black (or red) magneto ignition wire (which has a female blade connector) into the male blade of the coil (or it’s black or red wire with male blade). This isolates the circuit to just the engine and coil. Just remember you can’t turn the engine off.

Tomos A35 and A55 CDI ignitions

There are two types of Tomos CDI magneto ignitions, the A35 type (1994-2006) and the A55 type (2001-later). They consist of two or more coils mounted on a stationary plate, surrounded by a rotating flywheel with four strong magnets molded into it. The A35 ignition has no pulser coil to tell it when to spark. It triggers when the source coil voltage reaches a pre-set level. So changing the location of the source coil (by rotating the stator plate) changes the ignition timing. Tomos provides adjustment slots in the stator plate, and timing marks (thin angled black lines) on the crankcase (minimum and maximum ignition timing), at about the 10 o’clock pposition. An ignition timing strobe light is the only way to check the ignition timing. The strobe light illuminates the fast moving flywheel mark only for an instant. So it appears, magically, to be not moving. The fire mark on the flywheel should lie between the black lines on the case. It should not jump around. The light should not flicker. Once the stator is set in the desired position and the screws are tightened, the timing is set forever, and never needs adjusting (that is assuming the flywheel locating key is in its proper place and the flywheel nut is fully tight). Unlike the A35, the A55 ignition does have a pulser coil that signals the control unit when it’s time to spark. It’s an external pulser (or exciter or trigger) coil that senses a raised strip on the outer edge of the steel flywheel/rotor. So changing the stator position does not change the ignition timing. The A55 external pulser is fixed and mounted in a way that prevents it from being adjusted.

 Left, grinding away the plastic reveals the CDI circuit board and the coil of 233729. 

Figure 6a: A55 “no battery” ignition exploded view       Figure 6b: Same ignition shown in a semi-schematic diagram

         There are about ten different Tomos magnetos for the A35 and A55 engine series. They are all covered in detail in the wiring diagrams collection that this written text supplements. There are also a few more for the earlier A3 models. Before 1986, Tomos A3 mopeds had an external ignition ground that powered the brake light. On those early models if you unplugged the brake light, and then squeezed either brake, the engine would lose spark and cut out. Those early A3’s, with 3-wire magnetos, yellow,  black, and blue, often need the blue magneto wire to be grounded in order to have spark.  After ‘86, all Tomos magnetos are 2-wire magnetos, yellow and black, with no external ground, one less worry.       

Ignition timing

The spark occurs a little before the piston reaches top. That explains ignition timing in one simple sentence. Spark happens before top because the gasoline and air take a tiny bit of time to burn. If the spark happened right at the top of the piston stroke (“top dead center” or TDC), the engine would run, but be weak. If the spark happened twice as early as it should, the engine would run, but be weak and run hot. There’s a preferred range where the “porridge is just right”. Expressed in terms of crankshaft angle, the preferred ignition timing is between 10 and 20 degrees before top. Imagine the flywheel is a pie. Cut the pie in six pieces and you have 60 degree slices. Cut one of those pie slices in three thin slices. That would be a 20 degree angle. That thin slice is a little less than an inch wide on the edge of the flywheel. The time taken for the wheel to move that much is about the time taken for the gas to ignite. At 6000 rpm the piston rises every 0.01 second. Expressed in actual seconds, at 6000 rpm, the spark occurs .01*20/360 = 0.00055 seconds before the piston reaches top. That’s half of a thousandth of a second. You don’t need to know that to fix mopeds, but it makes the lesson interesting and amazing. The faster the engine turns, the less time the fuel has to burn. Because of this, most gasoline engines have variable ignition timing, rather than fixed timing. Four stroke engines like the timing to be about 10 degrees at idle, advancing to about 35-40 degrees at high rpms. They have vacuum advancers, centrifugal advancers, and electronic control units (ECU), to vary the ignition timing automatically. Two stroke engines like the timing to be about 20 degrees at idle, retarding to 10 degrees at high rpms. The explanation is better atomization at higher engine speeds makes smaller fuel droplets which take less time to burn. Before 1994, Tomos A35 mopeds had points, with fixed ignition timing, 20 degrees BTDC. From 1996 on, they had Iskra CDI, with variable ignition timing, 20 deg at idle changing to 10 degrees above about 6000 rpm. The only way to see the timing is with a strobe light made for automobile ignition timing checking. To actually measure the degrees, cars use a thing called a “degree wheel” that attaches to the crankshaft. Any piece of paper with accurate degree lines can be attached to the flywheel, but putting it in the exact correct position is difficult. There’s a clever and simple procedure for finding top. A tool called a piston stop is screwed into the spark plug hole. The crankshaft is rotated by hand until the piston is parked up against the stop. A line is made on the flywheel, adjacent to any chosen case mark. Then the crankshaft is turned by hand the other way until the piston is again parked up against the piston stop. A second line is made on the flywheel adjacent to the case mark. Then a tape measure is laid around part of the flywheel to find the midpoint between the two marks. That is “top dead center”. Fortunately the Tomos flywheels already have inscribed timing marks, one for top, one for fire, spaced 20 degrees apart. The F mark should be between the crankcase marks, when viewed with the strobe. The newer A55 engine mopeds have the same ignition timing but it is not adjustable like the A35 is. That’s Tomos saying don’t mess with a good thing.

Normally, ignition timing is never an issue with CDI ignition 1994-later Tomos mopeds. That is because those magnetos are maintenance free. It is, however, often an issue on the earlier points-ignition models. This is because the ignition timing gets retarded as the points rubbing block wears down. So points need adjustment (spread apart to have more “gap”), and lubing with high melting point grease, every few thousand miles. Besides that, they can be adjusted wrong. The points are designed to open at the right moment in a running engine, when at fully open in a stationary engine they have a gap of .014 to .017 inch (.35 to .45mm). In a magneto with points ignition, the spark happens when the points open, not close. That is essential to know. You can spot check the ignition timing of a points model with nothing but a pen and a flashlight. Find TDC with the pen in the spark plug hole. Rotate backward 20 degrees and see if the points are just starting to open there. In both points-ignition and CDI ignition, the flywheel can be installed in the wrong position on the crankshaft by leaving out the little locating pin. That’s not a normal thing. Neither is running with a loose flywheel nut until the pin shears off and ruins the crankshaft and flywheel. Ouch. It’s also not normal to have some other flywheel, like from a Puch, Sachs, or aftermarket one that has no timing marks or is sparking at the wrong time. A bunch of different moped flywheels will fit the Tomos crankshaft, but they might have the wrong ignition timing because of a different point cam angle. Some stator plates can be installed upside down, making the timing 180 degrees off. Only in these not-normal circumstances you might need to mark the flywheel and check the ignition timing.

 

Tomos A55 Ignition

Here are some pictures of a 2011 Tomos ST magneto.

Above, after 2009, the flywheel says “Kinetic 12V60W”. Rotation is counter clockwise. Since 2010, all models, kick start and electric start, have the outer gear for electric start. That gear blocks the view of the “pulser” or “timing coil”, black at lower right.

Above, a Tomos A35/A55 crankshaft held at the same angle as one in the engine. Roughly speaking, the cylinder is tipped forward to the 10 o’clock position. Here the connecting rod is pointing straight up the cylinder, which is “top dead center (TDC)” or the top of the stroke. When the crankshaft is in the TDC position the crank pin is at 10 o’clock. Then see the little hole in the tapered shaft pointing at you? It is where the flywheel “key” or “roller” or “pin” goes. The flywheel key is at 11 o’clock or 11:30. Right above the crankshaft is the black-wrapped ignition source coil, that’s fixed to the stator. In the upper right corner is the Kinetic pulser, black plastic that’s kind of rough. It is fixed to the crankcase at the 4:30 clock position. This angle, plus the crankshaft key hole angle, plus the angle of the “timing strip” on the flywheel, relative to the key groove (not shown), plus any retard or advance added on by the electronic module or “CDI unit”, is what determines the ignition timing.

Above, two views of the A55 “stator” or stationary part of the magneto. Three clear-coated copper lighting coils are seen at 9 o’clock, 12 o’clock, and 3 o’clock. The 90 degree spacing matches the four magnets inside the flywheel, not shown. The 3 lighting coils are connected in series, grounded internally, and emerge as the yellow lighting wire. Branching off one of the lighting coils is an additional white/red battery charging wire, not shown. At 6’oclock is the black ignition source coil, not connected to the others, emerging as the black ignition wire.  At 4:30 is a black plastic junction box. Also at 4:30, but further out, outside of the flywheel, is a rounded black plastic one inch cube called the “pulser” or “trigger coil”. It tells the CDI control unit when to fire the spark plug, at a precise crankshaft angle. Not shown is the flywheel or external “rotor”, with a raised strip of metal that triggers the spark timing. Notice how the white pulser wire is on the bottom and the black pulser wire is on top. If they are reversed, the ignition timing will be way (like 40 degrees) too early, and the engine will run poorly. The left photo is a 2007 stator, by AET, made in Slovenia. The right photo is a 2011 stator, by Kinetic, made in India. They are both good and interchangeable.

 

Ignition symptoms

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New Tomos Service

August 13, 2008

Welcome to Myrons Mopeds New Tomos Service department.

Here are some articles to help you repair or lovingly maintain your 1992-later Tomos moped. 

Tomos Engines is about the 1976-91 A3, 1992-06 A35, and 2007-on A55 moped engines.

Tomos Basics is a mini owners manual, that supplements the regular owners manual.

Tomos Oil Injection is about the simple but difficult operation of installing the left engine cover.

Tomos Throttle Upgrade is about the 1992-07 “throttle valve” sliding block that sometimes breaks.

 

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Tomos Basics

August 13, 2008

Table of Contents

1. Tomos Basics – supplemental owners manual info for new Tomos owners

2. Tomos Revival Battery Installation – there’s a trick to it

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              TOMOS BASICS for USA Models 2007-on (A55 engine)

  1. TOMOS means TOvarna MOtornih koles Sezana (motorbike factory in Sezana, Slovenia).
  2. Warranty is 6 month/4000 mile limited. Owner must send in the warranty registration card located in the owner’s manual to activate the warranty on a brand new Tomos.
  3. Engine is the A55 two-cycle 49cc  single, EPA and CARB compliant with catalytic exhaust. Speed is 30mph. Horsepower is 2hp. Transmission is two-speed fully automatic.
  4. Pedals go forward for hybrid human/motor propulsion. Pedaling speed is 5 to 10 mph. Pedals kick backward for starting engine. Pedal forward to put pedals in kick position.
  5. Gasoline is 90 octane minimum. Only Sprint model is pre-mixed with oil 50:1 or 2.5 ounces per gallon. All other models have oil injection and use straight gasoline.
  6. Gas tank size: LX 1.5gal   Sprint, ST 1gal.  Arrow, Revival, Streetmate .75gal. On the LX and ST locking gas lid, only the key turns, counterclockwise to open.  On ’05-08 Arrow, Revival, Streetmate the gas lid is push in. It pulls straight out. Sometimes it’s tight. After 2008 all gas lids are quarter-turn type.
  7. Gas valve is a manual fuel tap or shut off. It is located above the engine on the left side of the bike. It has three positions, off (horizontal), on (down), up (reserve). Use on during normal operation. Use off when not operating. Use reserve if you “run out of gas”. Reserve lasts 4 to 10 miles. Don’t forget to put it back to “on” after you gas up.
  8. Gas level is checked by opening the gas lid, looking, shaking, and listening. There is no gas gauge. On the LX you can see the whole tank. On the ST and Sprint you can see half way. On the others you can only see the first fourth. Many people choose to install a clear hose branching up from the fuel line. It serves as a gas gauge. The liquid level in the tube is the level in the tank. Gas tank vent: On Arrow/Revival/Streetmate models the gas tank is inside the frame, which is U-shaped. On one end of the “U” is the fill hole, where you add gas. On the other end of the “U” is a vent to let air in and out. It normally lets a tiny amount of air pass but not enough during refueling. When adding gas, the gas tank vent, a black spring-loaded push button, needs to be pushed each time the tank seems full to let any air escape allowing more room for gasoline. It makes a hiss sound. When the ¾ gallon tank seems full and the vent no longer hisses then it’s truly full.
  9. Gas mileage (mpg) is 100 miles per gallon, going 37mph on city streets. If you’re larger, have hills, rough roads, stop and go, your mpg (and range) will be less. If you’re smaller, more aerodynamic, and go slow, your mpg (and range) will be more.
  10. Gas range:  LX 125mi  Sprint, ST 85mi  Arrow, Revival, Streetmate 60mi. Means topped off to hitting reserve, 160lb rider on smooth flat city streets.
  11. Oil is two-cycle oil. It’s slowly consumed by burning along with the gasoline. Use a good brand, preferably synthetic, like Champion weed wacker oil. Without the oil the two-cycle engine will get hot, melt the sides of the piston, and “seize”, with a scary skid.
  12. Oil tank is under the seat, except Sprint, which is premixed in the gas. It doesn’t matter how much oil is in it, only that there always is some. Check the oil level at each gas fill-up. After several gas fill-ups it will need an oil fill-up. 13 ounces lasts about 5 gallons.
  13. Steering lock is on the left front of the frame. To lock, put the steering almost all the way to the right, push the key in while turning it to the right. Move the steering slightly until it finds the hole and goes down 3/8 inch. To unlock, turn the key to the left, pull up, and wiggle the steering if necessary.
  14. Keys: Sprint = steering lock only (2), no ignition key. No battery to turn off.
  15. Keys: ST/LX = steering lock (2) and gas lid (2), no ignition key. No battery to turn off.
  16. Keys: Arrow = steering lock and ignition (2). Turn off ignition and battery after use.
  17. Keys: Revival = steering lock, seat, and ignition (2). Turn off ign & battery after use.
  18. Keys: Streetmate = steering lock, seat, trunk, ignition (2). Turn off ign & bat after use.  Main key switch, also known as “the ignition”, on Revival is on left top of the fake gas tank. On Arrow and Streetmate it’s under the left side of the seat.
  19. Choke is manual. It’s needs to be on (flipped up) for starting when the engine is cold. After a few seconds, when the engine is warmed up, it needs to be off (flipped down). In winter, temp 40 F, the choke is left on for the first two blocks. For normal temp 70 F, the choke is left on for 10 seconds. In hot summer, temp 100 F, it’s not needed at all. Never leave it idling for long periods with the choke on or it will become “flooded”. Never use the choke when the engine is warm or it will become “flooded”. It’s better to under use the choke, than to over use it. If the engine becomes flooded, then it will need no choke and full throttle (maximum air) to compensate for the excess fuel that has accumulated. Running fast cleans it out, and is better for a two-stroke than idling.
  20. Starting:  Turn gas valve to “on”, arrow down. (or “res” if it’s very low on gas)
  21. Starting:  Turn engine stop switch to “run” symbol. It’s on the right handlebar.
  22. Starting:  Revival/Arrow/Streetmate only. Put the key in and turn it on.
  23. Starting:  Cold starting only. Put the choke on by flipping the black lever up.
  24. Starting:  Stand on the ground with the bike on its center stand. Pedal forward until the pedal on your side is in the 2 o’clock position. Have your left hand fingers on the left (rear) hand brake, ready to stop in case it comes off the stand and takes off. Have your right hand on the throttle, with the twist grip turned only just a little, or not at all. Now kick backwards. A broke-in new Tomos starts in one kick.
  25. Starting:  After it starts, rev it up by twisting the throttle. The engine needs to be revved up either stationary on the center stand or moving down the street. Starting it up and then letting it idle to warm up is not necessary or recommended. Its two-stroke crankcase already has the oil film, so it’s ready to ride immediately after starting.
  26. Starting can also be done with the tires on the ground, off the center stand. Pedal the bike forward, maybe 10 or 20 inches, to put one of the pedals in kick position.
  27. Starting can be done while moving. Just stop pedaling and kick backwards.
  28. Electric starting is on Arrow/Revival/Streetmate only. Use the above starting steps, but replace “kick backwards” with “hold the left brake and push the start button”. The start button is where your right thumb is. Then ride for 10 minutes to recharge the battery.
  29. Storage: Ride it with the gas valve turned off, to evacuate the gas from the carburetor. After about a block when it runs out, put the choke on and it will go another block. Doing this will prevent the carburetor from getting coated on the inside with tar from dried up gasoline during storage.
  30. Flooded Starting: Occasionally the moped can become “flooded”, a condition where too much gasoline and not enough air is causing the engine to not start. When this occurs, a different starting procedure must be used. First the gas valve should be turned off. The carburetor holds enough gas to run for at least a minute. Instead of minimum throttle with choke on (up), it needs maximum throttle with choke off (down), to get the most air. Once it fires, it needs the maximum throttle for awhile, maybe 5 or 20 seconds, until the rough running goes away. Then it needs 15-20 minutes of fast running to heat up the exhaust fully, to boil off any unburned gas and oil. During this period it will smoke a lot. If it does not fire within a few full kicks, then the spark plug will need to be removed and the gas or oil dried off it. If the white or brown porcelain insulator is shiny or black, then it will need a new spark plug, NGK BR7ES. Here are the causes of “flooding”. Knowing these before it happens will help prevent the problem.
  31. When a moped is leaned way over, especially with the gas left on, such as when it is being transported, gasoline can spill into the air filter or into the intake port of the engine, and result in not starting. This also can happen on Revival and Streetmate when gasoline spills over during filling. When the engine is run with the choke on too long, the spark plug can get wet with too much gasoline, and result in the engine not starting. Idling for too long, or going slow all the time can also cause this. When the engine is kicked over many times without having a spark, such as when the kill switch is left in the off position, the spark plug can get wet with gas and result in not starting.
  32. If the float valve inside the carburetor malfunctions, gasoline can spill into the air filter. A tiny fiber can cause that, or tar from a long time sitting, or a worn needle valve and/or seat. If the oil injector leaks oil into the engine during storage, then the spark plug can get wet with oil. Remove the spark plug, kick over the engine to push out any excess oil, and clean the oil off the plug.

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Tomos Revival Battery Installation

Left, two views of the Revival battery. It’s a common size used on most modern 49cc bikes with electric start. It’s a 12 volt 4 amp-hour, gel cell sealed type, BTX4L-BS or compatible. It has to lay sideways and the rear terminal wire has to be like shown, or else the cover won’t close all the way. Even when it is correct the cover has to be pushed tight to make the screw holes line up. 

Tomos Oil Injection

August 13, 2008

Tomos Oil Injection and Left Engine Cover Service

2011 Tomos ST with left cover removed.

Tomos has made oil injected mopeds, US models, for over 33 years, since the 1979 Silver Bullet. Ever since, every deluxe Tomos with oil injection has a small oil pump mounted onto the left engine cover, over the magneto. They have an excellent reputation. The highest mileage mopeds, in general, are the oil injected ones. When the engine is not too modified, the oil injection gives it the right amount of oil, automatically, all the time. You don’t have to mix the two cycle oil with your gasoline if you have oil injection. Serious commuters and most people in general prefer the convenience of oil injection and are willing to pay a little extra for it.

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Above, close up of 2011 ST flywheel. At center, the special nut with a groove in it for the oil injection pump. Until about the mid 2000’s, the magneto nut had two outer prongs that held an free floating aluminum disk with a groove in it. This upgraded nut has a steel disk rubber mounted and bonded to the nut. Click to enlarge any of these pictures.

Inside view of left engine cover showing oil pump tongue.

The left cover is easy to remove, but hard to put back. The tongue on the oil pump must be pointed in the same direction as the groove in the flywheel nut. Besides that, two precision 9.8mm sleeves, one at the upper cover bolt, and one at the lower cover bolt, must line up with their holes in the aluminum engine case. What is difficult is you can’t see it. It’s a “blind operation”, which is something that is done with your eyes closed, mostly by feel. When you think the tongue and groove are at the same clock position, say 12 o’clock, then you must turn the cover around and place it exactly on the two alignment sleeves. It usually never goes all the way on until you hit it lightly with the soft side of your fist. When it’s not lined up, it makes a thud or thump, and there is still a small, like 1/16 inch gap between the cover and the case. When it is lined up, hitting it lightly makes a loud clap, as the aluminum cover slaps or snaps together with the aluminum engine case.

On this flywheel nut, the oil pump groove is completely rounded. It no longer drives the pump.

As long as the person doing the service does the procedure properly (lining up the tongue and groove) and does not leave out the alignment sleeves, the oil injection performs reliably for many tens of thousands of miles. The most common source of trouble is improper servicing. When the tongue and groove are not engaged, there is a small 1/6″ gap between the cover and the case. If the three cover bolts are then installed and tightened down, the cover will be forced to go all the way on. Eventually the oil injection will fail when the groove hole becomes completely rounded out, and no longer engages the tongue. When that happens, the oil pump stops pumping, and soon after that the engine seizes up.

Tomos Oil Line Clamps and Oil Tank Repair

Tomos oil line clamps work good when they are put on right. Here’s all about it.

Left, factory installed clamp. Middle, spreading with a dental tool. Right, lifted over the lip of the spigot. You can see a green “tail” on the right of the cup. What’s funny is that is not the crack, but it looks like one. Slightly pressurizing the tank with air revealed that there was a crack, as oil was seen leaking out. The real crack is where the punch is in the middle picture. Nothing sticks to this kind of plastic, so plastic welding or tank replacement were the two options.

 

Left to right: 1) Spreading open the crack with a tapered punch. Then cleaning off the oil with spray solvent and compressed air. Then warming the plastic with a soldering iron, pushing softened plastic from either side towards the crack, filling the center. Then pulling the punch out to allow the tension to close the crack. After cooling the sealing surface around the hole is made flat with a disc grinder. 2) The plastic welded oil tank, ready to put back on. 3) An old pliers is ground away about 1/16″ from the end, to make an empty pocket for the loop part of the Tomos oil line clamp. 4) Squeezing the clamp tight with the special pliers. 5) The oil line is re-clamped properly. You cannot rotate the oil line or clamp, because it is tight. The loop of the clamp is not smashed, thanks to the cut away in the pliers.Click on the far right picture and you’ll see the rounded loop. When the loop is smashed, it can eventually break and come off. That can be a mess, or it can be a disaster.

Final Bleeding of the Short Oil Line

After the oil is put back in, the long oil line, which supplies the oil pump is bled by removing the bleed screw. Once that is done, only the short line from the pump to the engine is still full of air. The only way to “bleed” that is to run the engine on temporary gas with oil mixed in. It takes 5 or 10 minutes to go about 10 inches. The oil flows very slowly, about 3-4 drops per minute, at 7000 rpm.

 

Tomos Throttle Upgrade

August 13, 2008

Tomos 1991-2007 Throttle Upgrade

This is about how to repair an A35 throttle that has a bad “throttle valve”, in case the original part is not available.

Above, the bottom view of the throttle used on all A35 (except A35 Revival) and A55 models from 1992 to early 2008. Everything is black except the light grey “throttle valve”, also known as “sliding block”. It is Tomos part number 223707. Since mid 2008 the controls are different. They say TBS, and the throttle is a wrap-around type, so it has no sliding block.

Above, the same throttle with a pinch bolt upgrade. When the sliding block breaks or strips and cannot hold onto the cable wire, a throttle pinch bolt, 5mm diameter by 7mm long is installed on a new throttle wire just behind the broken sliding block. First a new throttle wire is installed and lubed. The old sliding block must be in otherwise good condition, other than it cannot hold onto the wire. A 5mm diameter by 7mm long throttle pinch bolt is slid over the end of the new throttle wire, and positioned against the sliding block. The wire is pulled taut. The screw is tightened with a small sharp proper fitting screwdriver, very tight. With the engine not running, the throttle is operated to see if it works and feels right. Then the excess wire is cut off, with a sharp wire cutters (diagonals), when the throttle is held at max, engine off. The short tail should be about 1/4″, like shown above. Bend the tail if it hits the grip at max position.

Above left, exploded view. Middle, broken 223707 with pinch bolt back up. Right, pinch bolt 5mm diameter x 7mm.

Warning. Improper installation or using a bigger or different pinch bolt might make the throttle stick or stay on. Many other things can also make the throttle stick, such as lack of lubrication, or a kinked or frayed cable. See Service/Carburetor for info about sticking throttles. Do not let anyone operate the moped if the throttle is sticking. It should always snap back to idle when you let go. This information is for service personnel and competent home mechanics, not just anyone. Please get help if you need it. Use discretion, and use this info at your own risk. The author assumes no responsibility for the use of this information.

Tomos A55 Transmission Oil Leak

August 12, 2008

Occasionally new mopeds, 2008 and later, leak transmission oil (ATF) at the front chain sprocket. The chain then slings the oil onto the rear of the bike. Here’s why.

With the distance bush removed you can see the thin o-ring #31 (033007). The white surface around it is the inner race of the big ball bearing #22. Click to enlarge images.

 

 

Sealing the coaxial drive is tricky. Oil can leak from three concentric circles.

  • 1. the circle between the central pedal shaft and the drive shaft #23
  • 2. the circle between the drive shaft #23 and the distance bush #20
  • 3. the circle between the distance bush #20 and the outer big seal #21.

1. Leaks from inside the drive shaft

Pressed deep into the center of the coaxial driveshaft #23 (223453) is needle bearing #24 (033502). It’s left end has a thin rubber seal. This generally does not leak except in some high mileage machines, or if it is damaged during installation of the pedal shaft by a sharp corner at the end of the pedal shaft, such as caused by crashing or abuse. Tomos intentionally rounds the left end of the kick starter/pedal shaft, so it can’t cut the seal as goes in. When this “inner” seal leaks, the whole engine must be completely disassembled, to replace the driveshaft #23 (223453 for pedal, 223456 for kick), complete, at a cost of about $150 parts and $250 labor. Total $400. This is Option 1A, the way Tomos says in the 1985 A3 Service Manual, “In case of damage to the needle bearings in the main shaft, we suggest it’s replacement with a new complete main shaft.”

Alternatively, the motor can remain installed and assembled, except for the transmission gears and shafts, which are removed from the right side. Then it is possible to remove the leaking left needle bearing from the drive shaft on the right side. A very special custom modified inner jaw slide hammer type bearing puller tool is necessary. Then the cost, in most small shops, is about $220 for making the tool, plus $150 labor, plus $30 parts. Total $400. This is Option 1B, for skilled toolmakers. It is not in any Tomos service manual. But Tomos does sell the parts to do it. 

Left, Tomos says in the 1992 A35 Service Manual, in case of damage to the inner main (drive) shaft seal or needle bearings, to remove them using a suitable tool, and install new ones with press tool 732.367. 

Right, the installer 732.367 with a 16mm to 20mm step. The extractor 706.485 and extractor bridge 706.472 are for extracting the 12mm ID left counter shaft bearing, and the 12mm wheel bearings. Apparently, Tomos does not say how to extract the 8mm and 10mm ID transmission cover bearings, and the 16mm ID drive shaft needle bearings, in any of their manuals.

Much skill and craftsmanship is required to select, make or reshape the tool. Otherwise it tears up the delicate needle bearing, leaving the thin shell stuck in the bottom of a deep hole. That mess takes hours to clean up. The bearings are painstakingly peeled off in small pieces, like peeling a stubborn steel orange that’s down in a tight hole. You can barely reach it and see it. But you save $100.

Left, a Tomos drive shaft 223453 showing the two needle bearings installed. The kick driveshaft 223456 is identical except it is smooth and flat where the ring of ramps is. This particular one has broken all of it’s ramps off. The deepest bearing 033502 has a rubber seal at the left (deepest) end. Above it is 033503, another needle bearing, not as wide and without any rubber seal.

Right, the puller in action. Below right, the bearings are out, but still on the puller.

 

 

Left, the two jaws must fit the 2o.5mm OD yet pass through the 16mm ID.  Wider jaw lips and more jaws would be better.

 

Left, the left sides of needle bearings 033502 and 033503. Right, the right sides.

 

033502 says “SNL  SCE109RS” and 033503 says “SNL  SCE108”. You can see the damage the puller did. You can see the black rubber seal on 033502, near the puller damage. When oil leaks from the center of the hollow coaxial drive shaft, rather than from under the surrounding distance tube 209077, it is from this seal, deep deep inside.

Right, the empty drive shaft with it’s bearings out, plus a thick rubber o-ring #30 (033006). The o-ring is an upgrade that comes on the newest bikes, 2012 and 2013. It is a heavy duty back up to the little seal in the left needle bearing. Left to right, the o-ring goes in the hole first, then the bearing 033502, seal side down, then the bearing 033503. These things are super easy to put in, just press straight in, with precise hammer taps. But they are super difficult to get out, even for professional mechanics.

 These two ways of fixing the inner leak, Option 1A and 1B, are very difficult and/or very costly. They are the options that use Tomos original parts.  

  

 

A better way is with a special sprocket nut, custom made. MM made and sold these from 2003 to 2010, but no more.

At left, the upgrade nut, uses a 32mm wrench, precision machined to accept an off-the-shelf 16 x 24 x 6 metric oil seal. At right, an original Tomos front sprocket nut, M22 x 1.0, uses a 30mm wrench. This is only for when the back side of the sprocket is bone dry, and the pedal shaft is dripping wet where it exits the drive shaft, which means the leak is from circle 1, inside the drive shaft only.

 

 

2. Leaks from outside of the drive shaft

Before 2008: metal to metal in three places

2A. The back side of #20 distance bush 209277 against the front side of the #22 bearing.

2B. The front side of #20 distance bush 209277 against the back side of sprocket #17.

2C. The front side of sprocket #17 against the nut #19 and washer #18.

After 2007: o-ring upgrade, no more metal to metal

2. The beveled surface of distance bush 209077, against o-ring 033007, against #22 bearing.

Before 2008, a scratch on any one of those metal surfaces would cause a leak. But that almost never happened. The parts were always made precise and smooth. What’s funny is that the oil seal #21 rarely or never leaks. Until ’07, only a loose sprocket nut caused a leak. The sprocket and distance bush were almays made flat and never leaked. In 2007 we started seeing wavey sprockets. Dished sprockets on Revival, Streetmate, Arrow had their washer tab hole too far in towards the center. Myrons used to weld part of that and grind flat. Flat 26T sprockets 209078 were made warped by the stamping. Also in 2008 many distance bushs had deep gouges in them.

Tomos upgraded the 209077 distance bush by wedging an o-ring in the corner of driveshaft #23, bearing #22, and the back side of #20, and cut a bevel (about 30 degree angle) cut on the inside back corner of #20, to compress the O-ring as the sprocket nut is tightened. Then the wavey sprockets didn’t matter, since the O-ring stops the oil from reaching the sprocket in the first place. Even though they had the right idea, there were several problems with the 2008-2009 O-ring-sealed distance bushes 209277. Some were installed beveled side out instead of in. Some were made without enough bevel, also cutting the O-ring #033007. The dark colored distance bushes, made in India, in the current (2009) parts inventory are made right. Their bevel is 2.6mm wide. At least some of the ones coming on the 2009-later bikes are made with only a 2.0mm wide bevel, which somtimes pinches the o-ring during installation.

At left is an actual distance bush. It’s made of tool steel. It’s from the current (Aug 2012) Tomos USA inventory. It’s well made and correct. OD=34.75 ID=30.40 H=10.92mm

 

 

 

Right, 3 distance bushes, L to R, cut too much – won’t squeeze o-ring, cut just right, cut not enough – can pinch o-ring.

 

Even with a new o-ring and distance bush, oil still can leak here. Once the o-ring is seated and everything is clean, a liquid gasket such as Three Bond can be applied to the inside of the distance bush. Then the distance bush is put in place carefully, trying to squeeze but not pinch the o-ring. More liquid gasket can be applied to the back of the sprocket. Then the sprocket is put in place. Some more liquid gasket can be applied to the center splines and and front side of the sprocket. Then the tab washer and 22×1 nut is installed and tightened, with liquid gasket on the threads. That tends to be the final answer. 

 3. Leaks from outside of the distance bush

 3. The inner lip of #21 (036620) oil seal, against the rotating outer surface of #20 distance bush 209277. This almost never leaks. The big seal, 036630, size 35 x 47 x 7mm, that you can see, seems to be the obvious guess. That guess is, 9 times out of 10, wrong. Replacing the big outer seal usually does not stop the oil leak (unless the seal was attacked by a screwdriver).

 

Horizontal Cross Section View of Driveshaft Assembly

Colors:  Pink = Transmission Fluid     Green = aluminum case         Note: the upgrade o-ring #30 is not shown

Tomos Balanced Clutch Drum

August 12, 2008

The Tomos two-speed automatic dual clutch drum, located behind the bulge in the right side of the transmission cover, is about 4 inches in diameter and made of two stamped sheet steel drums crimped onto a center tool steel precision shaft with gear. In the picture below, the view is of the outboard side, which is the first speed centrifugal clutch side. Flip it over and you would see an identical drum, facing opposite, with a small 1 inch straight-cut gear, the “first speed driving gear”, attached to the inboard side of the dual clutch drum, which is the second speed centrifugal clutch drum.

These drums can be made slightly out of round. They are machined on the inner surface only, where the clutch shoes slip and grab, according to speed. That machining is always perfect, as the inside surface is perfectly concentric with the one-way needle bearing. The proof is there is never any rapid pulsation during clutch slip. So the drum and clutches function perfectly. When the outer surfaces are out of round, the whole bike vibrates or buzzes, and gets worse when the engine is revved up going fast. That buzzing can be felt most in the hands and feet. It can make the mirrors blurry. It can make the speedometer go wild. It can make things on the bike crack, break off, or come loose.

When the drum is a little off balance, and the set of three clutch shoes is also a little off balance, then the vibration felt in the bike can become worse at times, more or less at random. This is because every time the bike slows down, the centrifugal clutches let go of the drum as the spring pulls them inward, and they begin to rotate inside the drum. Then when the bike speeds back up the clutches fly out and grab the drum, because of centrifugal force. But they end up in a new random location in the drum. If the heavy side of the clutch is opposite the heavy side of the drum, then there will be minimum vibration. If both heavy sides are together, there will be the most imbalance and the maximum vibration felt.

Other things can cause excessive engine vibration. Installing a heavier or bigger piston, like a 65cc, is the most common. Running with a loose flywheel or clutch nut is one. The magneto flywheels all seem to be balanced good, although they have not been tested. Using mis-matched clutch shoes is another. Not only should they all weigh the same, but they should all be equal in wear, not one new and two worn out, for example.

Above, the Tomos clutch drum. This one is extremely out of round, so bad you can see it with your eyes. Look at the thick wall on the left. Now compare that with the thin wall on the right side. Clearly the left side is heavier! When they’re bad they’re usually less than half this much. The out of balance clutches began around 2008. Before that, from 1976 to 2007 there was never any noticeable balancing or vibration problem. The A35 (1991-2006) and A55 (2002-later) have the same clutch drum. The A3 (1976-1990) one looks the same but parts of it are smaller or thinner.

Pressed into the center of the clutch drum is a precision roller clutch, a needle bearing that only turns one way. In the picture below, the roller clutch is installed correctly, with the plain side facing out, and the writing side facing inward. When you rotate an installed Tomos clutch drum clockwise, it engages the crankshaft. When you rotate it counter-clockwise, it spins free. When a Tomos engine seizes or hydraulics (that’s when the piston slams into incompressible liquid – gas or oil), the roller clutch can become damaged. It usually becomes tight or frozen. When a Tomos roller clutch is frozen, the bike will run fine but won’t go into neutral when you slow down to stop.

How to “balance” the drum:

A machine shop or a home machinist with a lathe, can perform a precision cutting operation. The drum is held by it’s inner surface, and turned in a lathe. The high parts of the outer surface are “skimmed off”. Try to leave the lowest part uncut, to give it the most strength.

 

Tomos Stripped Driveshaft

August 12, 2008

On pedal models only, not kick models, during the years 2008-2009, occasionally a driveshaft 223453 would become stripped at the ring of ramps needed for forward pedalling. This can never happen on kick models, because they do not have a ring of ramps. When the ring of ramps becomes stripped, the bike runs fine and kick starts backward fine, but the pedals just spin free going forward and do not propel the bike forward at all.

Left is a 223453 driveshaft brand new. Right is a 223453 stripped at the ring of ramps. No ped, only mo!

Some people live with it like that because it’s expensive to repair. The cast iron chips need to be flushed out, or else one chip can damage any one or even all of the gears. It’s too big a gamble to leave them laying in the bottom back corners of the transmission compartment. If the bike is ever leaned way over, the little iron chunks and bottom oil sludge will be poured over the gears.

More to follow…

 

Tomos A55 Derestriction

August 11, 2008

1. Removing intake air flow restrictor

This is the 2010-later carb, with red silicone over idle mixture screw. The PHVA14 has an idle speed screw, with a big knob sticking out for the rider to use occasionally, and a idle mixture screw, recessed with a slot head, for the service technician to use.

The “elephant trunk” restrictor is exposed, a hidden part of the junction sleeve 233748 that joins the air filter/silencer to the carburetor.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This is after the rough cut.

This is after smoothing and rounding with a rotary file.

 

 

 

 

 

 

 

 

 

 

 

 

2. Replacing the rear sprocket

Sprint, ST and LX models come with 28 tooth. Replace that with 22 tooth and subtract 3 chain links.

Revival and Streetmate models come with 31 tooth. Replace that with 24 tooth and subtract 4 links.

 

 

 

3. Shortening the stock exhaust

Only welders and metal workers can do this. But the benefits are huge. Speed increase from 37 to 43 mph.

 

 

 

 

 

 

 

 

 

 

 

 

Encarwi Service

May 4, 2008

Encarwi Carb Service for Tomos A3 1974-83

This very simple, early Tomos carb is designed to be serviced without removal. After 1985, Tomos A3 & A35 models came with Dellorto SHA14/12 carburetors. The Tomos A3 carburetor is in a confined area above the engine and below the sheet metal gas tank/frame. It is difficult to remove.

 Two super usfeul and easy checks:

1) Check the jet. With a large flat head screwdriver or a 9mm wrench, remove the jet holder #2. Remove the jet #2 with a medium-thin flat head screwdriver. Hold the jet up to a light source, such as a sunny white wall. Look through the tiny hole to see if light gets through. If it’s pitch black it’s completely blocked. If it’s not circular then it’s partially blocked, like by a fiber.

2) Check everything else. When the jet holder is removed, and the gas valve is turned on, gasoline should flow out of the gas tank, through the banjo bolt #16 at the float top #12, and then dribble out the hole where the jet holder was. This is a way to quickly test the fuel system, tank, valve, line, filter, and float, all at once.

If gas does not spill out with the jet holder removed, then gas is not getting to the jet. Check if gas comes out of the tank. If gas is getting to the carburetor, but not getting to the jet, then either the inlet banjo #14 or banjo bolt #16 is clogged, or the float top #12 is clogged, or the float #11 is in upside down, or the float is stuck in the up position. Several things can cause this kind of float to stay up and not drop down and let gas come into the float bowl reservoir: being installed upside down (pointy end goes up), rust powder filling up the guide hole at the bottom of the float chamber, the float bulb being pushed too far down the rod, the wrong float, or a dented float chamber wall.

 

Servicing

The jet holder #4 unscrews from the left side. It holds the jet #3, Bing 3.5mm size 46.

To remove an old, hard, shrunken and very stuck on, fuel hose, be careful not to break off the “neck of the banjo”. That means you only pull straight out and rotate, never pull or twist sideways. If that fails, a diagonal pliers aka dikes aka wire cutters, can be used to cut the old fuel line, parallel to the hose, without cutting the banjo underneath. The cut does not need to go all the way through the old fuel hose, but far enough to weaken it.   

To service the float, loosen the clamp screw #20 and rotate the carb so it is tipped to the right. Remove the 11mm hex head banjo bolt. Remove the two slot head screws #18. Lift off the float top. Lift out the float with your fingers. It should lift out freely and not feel stuck.

Float versions, left 70’s bulb, right 90’s solid

 

 

 

Things that cause not enough gas:

Rust powder filling up the guide hole at the bottom of the float chamber. Remedy is twisting a correct size drill bit with your fingers, to pull the powder up and out of the hole. With the jet holder removed and the gas valve turned on, gasoline should flow out of the tank, through the float valve, and spill out the jet holder hole. The amount should be enough to fill the float reservoir in a few seconds, which is roughly a spoonful every 4 seconds.

The bulb being pushed too far down the rod. Remedy is to push it back up. See the above photo with measurements.

Dented float chamber wall. Remedy is to grind or sand down the high spot.

Blocked float reservoir air vent. Gasoline cannot come in unless air can get out. Remedy is to find where it is blocked at, and remove the blockage. The vent follows a channel in the back mounting surface. An empty float reservoir should fill up in a few seconds after the gas valve is turned on. To test for a blocked air vent, first empty the reservoir, then turn the gas valve on for 8 seconds and then off. Then remove the jet holder, allowing gas to dribble out, to see how much gasoline there was in the reservoir.

Blocked gas tank air vent. Gasoline cannot leave the gas tank unless air comes in. So there is a pin hole in the gas cap. When the tank is full, and the vent hole is blocked, the bike will seem to run out of gas. To test for a blocked gas cap vent hole, first fill the gas tank, then close the gas valve, then remove the fuel hose. Place a clean container under it (to check for purity and to put the gas back in the tank). Turn on the gas and observe the flow. It will flow normal at first. But in a few seconds, as negative pressure builds up, the flow will slow down and stop, if the vent is blocked. If the flow continues for 20-30 seconds (or indefinitely) then the gas tank is vented.

Things that cause too much gas:

Worn float needle tip. Remedy is to sharpen it. Examine the tip with a magnifier. Spin the float with a drill while pressing the tip gently against a sheet of emery cloth or very fine sandpaper, at the same angle, and move it slowly around to fresh parts of the sandpaper. The needle rod must be straight first. Examine the tip with a magnifier. There should be, everywhere on the cone tip, circular sanding marks, and no more circular “potholes”.

The needle is bent. Remedy is to straighten it. Normally the bend is just above the top of the bulb. It is done with just fingers and eyes. Rotate to see which way it needs to go. Bend a little. Repeat. 

The bulb being pushed too far up the rod. Remedy is to push it back down. See the above photo with measurements.

Worn float seat hole. The float valve seat is part of the float top. It is the tiny hole at the bottom of the small hole. Examine the hole with a magnifier. It should be perfectly circular and free of nicks and scratches. Polish it with a spinning tooth pick, or the stalk of a Q-tip. 

Float bulb has gasoline inside it. If the float too heavy, it won’t have enough buoyancy to stop the gasoline from getting in. Remedy is to evacuate the fuel with compressed air, locate the leak hole, and apply a minimal amount of fuel tank sealant. 

 

Servicing the M56 engine’s H12 or H8 Carburetor:

One problem unique to this carb is warping of the engine side surface. This is caused by over tightening the two mount bolts, and maybe also because the heat block behind it is semi-soft. The back side must seal not just air, for good idling, but also there is a fuel passage that can leak because of a warped carburetor body. The remedy is to grind the back side flat again, without taking too much off. In the body, there is a narrow fuel hole at the bottom of another hole, that is impossible to see directly. That hole must be checked and cleaned with carb spray and compressed air. 

The float is the same as the other carbs. The float top is the same except it has no air vent pin hole. The idea was to not let gas spill out the vent hole. Instead the vent goes to the mounting gasket, where there is a small opening to the atmosphere, higher up.

 

 

 

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