Balancing flywheel/PP/clutch assembly, For my winter AX upgrades Options

[Chris Pincetich]

I just received a 13lb flywheel in the mail yesterday from Dominic (IMG:style_emoticons/default/beerchug.gif)
I've read about the advantages of having the engine rotating mass balances, especially in race engines and those that see high rpms a lot. I am putting this med weight flywheel in my stock 1.7 for AX when I do a side-shift conversion in Feb.

What's the best plan for installing this flywheel?

Some say (i.e. Jake Raby) that if you can't dynamic balance every last bolt then don't bother.

I'm thinking I want to send this mildly used flywheel for balancing. Would it be a waste of time and $$$ if the internals of my engine are not part of the balancing (i.e. crank)??? I can remove the clutch and PP (and bolts and gasket(?)) have this entire assembly sent for balancing...that seems like the best plan, but means having the car up on jack stands for the duration of the machine shop work (IMG:style_emoticons/default/dry.gif)

Any referals to a competent shop in the SF Bay area close to Oakland are greatly appreciated! (IMG:style_emoticons/default/beerchug.gif)

[Twystd1]

I have something interesting you guys might enjoy.

Suppose you balance a crank to zero. (Close as we can get)

Then you seperetly balance a flywheel to zero.

Then you match the flywheel bolts weights the same.

The assumption would typically be that if you now bolted the flywheel to the crank with said matched bolts.

And you put this combination on a balancer. It should run about zero balance as a pre-balanced assembly..

And you might be very WRONG.

I have done this myself. On a high end Sunnen digital balancer.
(Note I caliberated the balancer twice in this process to make sure I wasn't getting bad data)

I assumed that the package would be almost zero and not need any or very little metal removed.

This was not the case. When you hang a 14 LB flywheel on the end of a crank. It changes the harmonics of the crank. It also changes how the crank TWISTS. Thus the mass of the crank throws are moving a bit and changing the balance of the crank.

I was yanking metal out of that crank for hours. And each time I re-spun it up. It would change dramatically.

Please understand. I am not a machinist. I don't really know shit about this. I just hang out with guys that do.

So I suggest to you the following. Just because all of the pieces of a reciprocating assembly are matched in weight.
Does not automatically make a balanced "COMPLETED" assembly when bolted together.

When a type IV crank is spun up on the balancer with Flywheel, FW bolts,
and bob weights to equate what the rod, rod bolt, piston, pin and keeper weights. The crank MAY balance out differently.

AS far as the PP. This is also part of the equation. And must be indexed at the time of balancing to make sure it all goes back together with the same index. (FW and bolts also)

I wish I could explain all the reasons for this. problem is I don't know the answers.

I have simply seen this happen at other high end machine shops. And have encountered the same myself on 2 of my own builds.
(note: both times I chucked the crank and used another one. And yes they were magged for cracks)

AND.... This does not always happen. In fact it is rarely happens.
Some assembly simply balance out dead on or relatively close when assembled. And some are a serious cluster fuck to get it back to zero after ALL the pieces are put together and placed back on the balancer.

So I reiterate. I don't know shit. I just don't want to see one of the guys have this anomaly happen to them.

For myself: I have all the pieces of the assembly balanced as a WHOLE after each piece is weight matched and the crank and FW are balanced separately.

I wish Jake was here. He probably knows the answer to this anomalous stuff.

Just something to think about.

Clayton