This is from the Haynes “Honda 4-Stroke Mopeds 49cc PC and PF OHV models 1970-on” service manual. It is the same engine as Indian.
xmm-0.0..0 ft-lbs torque specification
0M5-0.0 5.1-8.0 valve adjust nuts
0M6-0.0 5.8-8.7 valve cover nuts
0M6-0.0 6.5-8.7 head nuts
0M6-0.0 5.1-8.7 case and cover bolts
0M6-0.0 6.5-8.7 camshaft and intake bolts
M10-0.0 22-28 flywheel and clutch nuts
M12-0.0 15-22 oil drain plug
The Indian service manual does not state the compression pressure or the compression ratio. But the Indian motor is a copy of an earlier Honda PC50K1 motor. The Haynes “Honda 4-Stroke Mopeds 49cc PC and PF OHV models 1970-on” service manual does state the compression ratio, 8.5 to 1.
The compression test pressure can be calculated from the compression ratio, the displacement (swept volume), atmospheric pressure at sea level (14.7 psi), and the ideal gas law.
P2/P1=V1/V2 P2/14.7=8.5 P2=125 psi relative to a vacuum
Minus the atmosphere, about 15 psi P=125-15=110 psi this is the ideal pressure
Actual “new” compression pressure would be 5-10 psi less than ideal because of leaks and the small additional volume of the pressure gauge hose.
So Pnew = 100 to 105 psi So over 95 psi is good, under 90 psi is bad
Here is an Indian engine, minus head and magneto. Red arrow is crankcase vent. If it is blocked off or clogged, the bike only run for awhile. Blow-by past the rings causes the pressure to increase. The high crankcase pressure cancels some or most of the intake vacuum suction pressure.
Right, close up of the fresh cylinder wall. You can see the reflection of the marks on the piston crown on the exhaust side (back) cylinder wall. A new Indian 42mm ring with a gap of only 0.007″ shows there is almost no wear.
The Haynes PC50 manual states the cylinder wear specs):
42.00 – 42.02 mm Cylinder (cast iron) bore diameter wear limit 42.1
41.98 – 42.00 mm Piston (aluminum) skirt diameter
0.10 mm (0.004″) Ring gap minimum
At right is page 14 from the Indian Service Manual showing the timing marks on the cam.
Indian Magneto Service
A. Indian Moped: 4-Coil Magneto – Wires Service
The entire Indian WTEMCO flywheel/magneto is Bosch compatible. Indian has the same engine, controls, switches, and wiring as a Honda PC50. It looks like the light green wire goes to the ignition armature, but there is no connection. The ignition armature has a support tab for the battery charging coil next to it. That tab is the black dot in the wiring diagram, where the light green wire originates.
Testing for spark is done with the essential wires connected. Stationary testing for continuity is done with the essential wires disconnected, as shown below.
When each test is performed, the wires are wiggled and prodded to see if the ohms reading changes. Sometimes a conductor will conduct until it is moved a certain way. Sometimes an insulator will insulate until it is moved a certain way. During each test the tester is tested by either disconnecting or connecting the test leads. Most ohmeters do not have a sensitive enough scale to go down below 1 or 2 ohms. Sometimes “testing the tester” by shorting the test leads, shows the slight difference.
B. Indian Moped: 2-Coil Magneto – Wires Service
The entire Indian WTEMCO flywheel/magneto is Bosch 90mm compatible. Early Indians had 4-coil, while most have 2-coil. The 2-coil magneto has the ignition coil (45mm bolt spacing) on the bottom and the lighting coil (52mm bolt spacing) on top, like the 4-coil. But the two outboard battery charging armatures on the 4-coil have been incorporated into the single lighting coil on the 2-coil. The connections and function is all the same, as is the troubleshooting. One good thing about Indian magnetos is that both kinds have an internal ignition ground. It is on the lower left armature bolt. On many mopeds it is external, and part of the brake light.
Once again, the ignition part of it is the same. In fact, schematically it’s the same for all points-magneto ignitions. Imagine a fork with 3 prongs: one prong is points, one prong is condenser, one prong is source coil (armature). The three prongs join together as one, the handle of the fork, which is the wire going to the ignition coil (transformer). To static test each prong separately with an ohm meter or continuity tester, the wires detach at the points with eyelet connectors. See above for the exact same procedure. As a reminder, checking for spark is completely different and separate from checking the ignition components for continuity. Checking for spark is done with everything assembled and connected, with essential wires grounded, if any, and “kill” wires left disconnected.
When a condenser is replaced, the lights coil is unbolted, and the new condenser wire is laid under it, to prevent it from rubbing against the rotating flywheel points cam. The thicker lights coil will pinch the condenser wire unless it is positioned in the corner before the coil bolts are tightened. Verify it and all other wires are not being pinched by tugging on them and feeling or seeing if they can move freely.
Indian Magneto Substitution
The entire 82mm WTEMCO magneto is a 90mm Bosch compatible. Any 90mm Bosch magneto will bolt on and fit, both the 3-bolt stator plate and the flywheel. However, the ignition timing in the flywheel is different on the various Bosch flywheels. An Indian flywheel has the same timing angle as a Tomos. Both of those bikes can take an entire Puch magneto, but it must be installed without the woodruff key, and positioned at the correct timing angle. It must be very tight, and can still slip later. Many of the modern CDI ignitions require that the woodruff key be left off, and the flywheel positioned at a particular angle on the crank. Such is the case if someone wanted to run a modern CDI ignition made for a Puch, on an Indian. Some more talk about this is in the Indian parts section.
The stationary part of the magneto, the stator, can not be substituted with a 90mm Bosch moped stator, such as one for a Puch.
If the entire magneto is substituted, the 5 or 6 Puch wires will have to become 3. On a Puch 6-wire stator, 2 of the output wires are actually grounds (green/black = brake light ground, and blue/black = ignition ground). Once they are grounded, and the grey tail light wire is left unused, then a Puch 6-wire will directly substitute for Indian 3-wire, blue for blue, yellow for yellow, and green for green. Knowing this should help many Indian owners that have very bad stators or none at all.
The armatures on a Bosch stator (Puch) are 54mm hole spacing, both upper and lower mounts. The WTEMCO Indian ones are 52mm on the upper (lights) and 45mm on the lower (ignition). So Puch armatures don’t interchange with Indian ones.
Notes about Indian magneto substitution:
With the piston is parked at top dead center, the rod is in the 12 o’clock position, straight up in this view. The woodruff key for the magneto flywheel is in the 1:15 position, or about 38 degrees. A Puch 1-speed crank has the same size and taper, but the key in the 12:00 position. However, a Tomos crank does have the same size, taper and key position as an Indian. Too bad early Tomos magnetos are scarce because they get rusty from trapped water. 1996-2006 Tomos A35 CDI-ignition, with 70 watts of lights power, magnetos would substitute if the coil is changed to the Tomos A35 coil with CDI unit built-in.
Ignition Coil Substitution
The Wtemco coil bolt hole centers are 58mm apart. The Bosch coil holes are 53mm. That is not so bad, but the metal plates are taller. Since the Wtemco coil plates are already up against the floor plate of the frame, there is no room for a Bosch coil in the same location. It would have to be hung with one bolt, at an angle. Furthermore the Bosch bolt holes are for 5mm bolts, whle the Wtemco ones are 6mm. So a special step stud 5-6mm is needed. Fortunately there are some 5-6 step studs on a Motobecane, that are the correct length.