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Balancing flywheel

blind_elk
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blind_elk Grand Master

blind_elk

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My bits of engine have come back from the machine shop. Part of the work they did was a balance on the crank / flywheel / clutch.

The guy I got to re-asssemble the engine is now all up-in-the-air because the machine shop has drilled into the side of my light-weight, CNC-machined, billet Aluminium flywheel to balance it. The "hole" is right under where a counterweight had been fitted to the pressure plate (at manufacture time). My engine guy reckons the machine shop should have simply moved the little counterweight, &/or added weight to the pressure plate only. The people I got the flywheel from in the first place reckon it's done all the time (removing metal from the flywheel).

What should I do? Should I complain to the machiners, or tell my engine guy to get a life? Any (constructive / instructive) comments appreciated.

TIA

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SteveL Mentor

SteveL

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Greg - the way it's normally done is:

- check run-out prior to balance (flywheel and fitted pressure plate).

- balance flywheel and pressure plate separately

- balance flywheel and pressure plate as an assembly.

It's quite normal to drill the outside of the flywheel to remove material to achieve balance. They obviously followed their usual practice and just weren't aware of the significance of the counterweight.

At the end of the day I wouldn't lose any sleep over it.

blind_elk Grand Master

blind_elk

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Thanks Steve. I would hope that they understood the significance of the counterweight. After all, I'm sure it's not the first one they have done.

That aside, why would the flywheel not be in balance in the first place? I guess the metallurgy wouldn't necessarily be perfect, so that some portions of the billet might be denser than other areas, right? Or the gear teeth attached to the outside rim might not be perfect, right?

Duncan Grand Master

Duncan

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Thanks Steve. I would hope that they understood the significance of the counterweight. After all, I'm sure it's not the first one they have done.

That aside, why would the flywheel not be in balance in the first place? I guess the metallurgy wouldn't necessarily be perfect, so that some portions of the billet might be denser than other areas, right? Or the gear teeth attached to the outside rim might not be perfect, right?

Interesting question? When they balance the full motor they need the flywheel and clutch as well as all the internals, is each component balanced individually or is the the total rotating mass that is in balance?

xRHETTx Mentor

xRHETTx

Posted
Posted

I'd assume that if at all possible that each individual component would be balanced seperately, then they would be assembled and balanced again as a whole.

This way it would keep the material that would have to be removed to a minimum.

The flywheel would probably not be balanced to a high precision straight from the factory, as all manufacturing processes are less than ideal, and most people probably wouldn't be keen on paying an extra $100 for a closely-balanced flywheel.

blind_elk Grand Master

blind_elk

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Interesting question? When they balance the full motor they need the flywheel and clutch as well as all the internals, is each component balanced individually or is the the total rotating mass that is in balance?
AFAIK, the pistons are made the same weight, the rods are made the same weight. Then presumably the piston/rod assemblies all weigh the same. So the reciprocating mass is balanced.

Then the crank is matched to the flywheel / clutch, so the rotating mass is balanced.

SteveL Mentor

SteveL

Posted
Posted
That aside, why would the flywheel not be in balance in the first place? I guess the metallurgy wouldn't necessarily be perfect, so that some portions of the billet might be denser than other areas, right? Or the gear teeth attached to the outside rim might not be perfect, right?

Manufacturing (machining) variations - even on a supposedly symmetrical component. While it's theoretically possible to get very tight tolerances using the best equipment, the cost would be prohibitive.

Metallurgical variations would be insignificant in this context (for a component machined from plate/billet...castings can be another matter).

SteveL Mentor

SteveL

Posted
Posted
AFAIK, the pistons are made the same weight, the rods are made the same weight.

Pistons are sold as a balanced set, as are rods. But manufacturing tolerances for balancing on mass produced engines are not as tight as you would use for a performance/race engine.....again mainly for reasons of cost.

blind_elk Grand Master

blind_elk

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Pistons are sold as a balanced set, as are rods.   But manufacturing tolerances for balancing on mass produced engines are not as tight as you would use for a performance/race engine.....again mainly for reasons of cost.
Didn't mean "made" as in "manufactured", I meant "made to be", ie adjusted to be all the same weight. If you get my drift.
Cubes Grand Master

Cubes

Posted
Posted

I had my rb30 balanced up.

Every rod looked like it had been touched, almost every rod bolt.

Everything looked like it had been slightly touched to achieve a balance.

Even the wiseco forged pistons had a slight nick as they were obviously not all equal.

I was suprised when the rod bolts weren't equal weights. :O

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