Crankshaft ignition taper

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Crankshaft Tapers

Measuring the taper on your crankshaft

This guide shows different methods to measure the taper of a shaft.

Thanks orangerobin for the reference.

Usr www users phreakco decepticon img forums ma forum performance 1294855941 tapers-1.jpg

Tapers of common components

According to Naz, "Most of the ones I’ve done all seem to be 5 degree, except the silly french of course, which is 4 degree's"


Taper Small End Dia (mm) Large End Dia (mm) Taper Length (mm) Taper (mm/mm) Resulting Angle (Degrees) Taper (Degrees)
Motobecane Ignition 12.70 14.95 23.75 0.0947 2.7 5.4
Peugeot Doppler Non Enduro (Fits Ducati CDI). 13.04 15.90 27.50 0.1040 ~0.10 3.0 6.0
Peugeot Doppler Enduro 441283 12/2009 "Problem Crank" 11.4 15.9 23.0 0.196 5.5 11
Pug MVT Premium Internal Rotor 13.40 16.00 31.87 0.0816 2.34 4.7
Puch, Tomos, Derbi, and Sachs 505 Ignition N/A 15 18 - 5 10

Cutting a Taper

Octavio: I just cut the taper for a Puch shaft last night. 5 degrees was dead on. My major ID ended up being 0.59” (15mm).

Here is the procedure for those who haven’t done this before: 1. Set your compound slide angle to your taper angle. 2. Square up your tiny boring bar. 3. Take passes of material off using only the compound slide axis. 4. Creep up to your final ID checking fit with your crank during the last 0.01”(0.25mm). 5. If you’re not super confident. practice on a piece of Al stock ahead of time.

This procedure is pretty obvious to those that have a lot of machining experience, but if you like me and have some, but not loads, it takes some thinking and doing to get this all figured out. I practiced on a piece of Al stock before chucking up my actual rotor.