For the second time lately, a MA user has PMed me asking, "I want to upgrade to a CDI and plan to use the Moby La Partie CDI which I read is for the large taper crank. How do I know if the crank in my motor is a large taper, thus correct for this advertised CDI?".
Good news is if you already are running points then you certainly have the early model "large" taper crank. Another may ask, "I got a basket case bike with no ignition and I need to know what my options are."
Knowing what taper the crank is that is looking out of the cases is going to determine what ignition you will be able to run. If it turns out to be a large taper, you will get off easy and can run the cheap 75.00 La Partie CDI, or convert the motor to a points setup.
If it is a small taper then your limited to a select few very expensive and sometimes complicated as well as fragile CDI units designed for high performance or racing.
The pictures below will help you identify if you have a big (points style) or small (CDI) tapered crankshaft.
I managed to find two known crank examples. The first is bare and is a small taper crank from a Peugeot SPX bike which is identified my the knurled shaft on the variator side. I did some research and found that all cranks sold for the SPX are small taper. The other shown in the case, is a stock points style large taper crank.
Measuring in millimeters with my calipers this SPX cranks taper reads about 23.5mm long from threads off to the end of taper.
I don't carry my calipers around so if I found a crank at a swap meet I might find a ruler. In inches the small taper measures 15/16 of an inch long.
The stock large tapered crank for points measures just under 27.5mm long.
The large taper again measured with a ruler comes in about 1 1/16" long.
So I guess an easy rule to base the differences on is to just remember"one inch". If the taper is over one inch it's a large taper points style crank. If its under one inch it's a small taper "money bags" crank.
If you have any questions about this method I suggested, or are having trouble contact Cheetahchrome http://www.mopedarmy.com/forums/profile.php?6,26847