DIY Flywheel Truing Stand
Article by Mark Trotta
A flywheel truing stand is a nice luxury, but homemade units work just as well.
A length of 4" C-channel stock is the base of this Harley flywheel truing stand. The metal was cut with a Milwaukee Portaband.
The alignment of the two center bolts on the truing stand is not super-critical. They just provide the two points that the flywheels and shafts ride between.
The adjustable magnetic base allows many options as to where it can be mounted. It's best to clamp to a surface firmly, and as close as possible to the shaft.
The indicator is positioned so the stem is parallel to the direction of component motion.
Shop: Magnetic Base with Dial Indicator
Having dial indicators on both sides makes measuring easier, but you can probably get by with one dial indicator, but you'd be moving it from side to side to get readings.
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Truing vs Balancing
Truing is about how the two flywheels mate to each other. Balancing is about the actual weight of the flywheels, spoken in terms of grams.
Truing is done at the factory, as is balancing, but not to the same degree of precision as would be required for racing.
Truing is mandatory, balancing is optional.
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Other Uses
Before reassembling the flywheel assembly on this Ironhead Sportster, I modified the truing stand to check run-out on the sprocket shaft and pinion shaft.
Check Shaft Straightness
When rebuilding a motorcycle transmission, it's a good idea to check the mainshaft and countershaft for straightness.
The picture below shows checking mainshaft straightness on the homemade flywheel truing stand.
This transmission main-shaft measured an acceptable run-out of .001". Anything past .003" is questionable.
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