Balancing flywheel

[blind_elk]

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

[SteveL]

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]

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]

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]

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]

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]

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]

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.

Yes....acheives the best result overall.

[SteveL]

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]

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.

[SteveL]

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.

Fair enough

[Cubes]

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.