[DeTomaso] Balance, was Re: I *hate* it when that happens....

[Ken Green]

Guy,
 
    I once complained that if you ask 3 mechanics the same question you will get 3 different answers, and a friend commented that that you will actually get 5 different answers.
 
    Having said that, the friends name is Jerry Yost, he vintage races a real GT350, and use to have a vintage NASCAR which he took all over the country.  He said he supported his hobby by building engines for other vintage racers and seems to have a lot of experience.  He's one of those guys who has the skill and tools to fabricate what ever he wants.  Kinda what I dream of when I grow up (probably too late now, LOL)
 
    His view is that if you buy a crate motor there is a possibility that for some unknown reason the builder may have played around with the balancing.  Maybe some engine builders prefer to fine tune the balancing at the crank not the flywheel (just guessing)?  Jerry said that you can take the original flywheel and pressure plate to a balancer and they can verify any variation for the standard imbalance and duplicate that in replacement flywheel and pressure plate.  I suppose that if the position of the pressure plate on the flywheel is not indexed, you can assume that the flywheel and pressure plate were not balanced as a unit, and assume the flywheel has the standard balance.
 
    In my case, I had a new diaphragm pressure plate I wanted to use on an older flywheel.  3 of the 6 holes lined up (the diaphragm PP had 6 evenly spaced holes, but the flywheel was drilled for 3 pairs of holes).  I bolted the PP on with 3 bolts, and center punched, drilled, and tapped the 3 other holes.  But when I bolted the PP on using studs (it's an aluminum flywheel), there was some play before I tightened the nuts on the studs.  I did a little research, and fold out that at some point (somewhere in the 80s?) Ford started using dowels to position the PP.  So I twisted the PP in one direction to center it as well as I could on the studs (there really wasn't that much play), and center punched and drilled holes for the dowels.  After all of that (figuring out what I had to do was much more time that doing it), I concluded I should have the flywheel and PP balanced as a unit.  One interesting thing is that the balancer noticed that
 washers I had under the nuts were not all identical and if the flywheel and PP were balanced with the washers in one location, and they were switched later, it would throw off the balance.  He removed the washer for the balancing and I have to make sure I have 6 identical weight washers for the final assembly.  All kind of a hopefully positive learning experience.
 
Ken
 
 
From: Guido deTomaso <guido_detomaso at prodigy.net>
To: Pantera REALBIG forum <detomaso at realbig.com> 
Sent: Friday, March 23, 2012 8:24 PM
Subject: [DeTomaso] Balance, was Re: I *hate* it when that happens....

@Dan, not sure I share your trust that any off the shelf flywheel will be 
balanced exactly the same.  Come to think of it, with that offset weight, how 
might one check one flywheel vs. another?

Relatedly,

@Ken, how does your buddy match the balance of a new flywheel and / or PP to the 
old one without bolting it to the crank it was balanced to and spinning it?  
Assuming the flywheel and PP were drilled to balance the crank, they're 
"off-balance", and duplicating that off-balance on replacement parts separate 
from the "reciprocating assembly" seems a tall task.

Thanks,

Guy D.




________________________________
From: Daniel C Jones <daniel.c.jones2 at gmail.com>
To: Pantera REALBIG forum <detomaso at realbig.com>
Sent: Fri, March 23, 2012 9:48:18 AM
Subject: Re: [DeTomaso] I *hate* it when that happens....

> Although I sent my aluminum flywheel to have it balanced with the engine
> when it was built, it's my impression that this step wasn't done. :<(

That was done for a reason.  Dave balances his reciprocating assemblies
to a spec flywheel (in this case 28.2 oz-in) so if the flywheel ever
needs to be replaced, any 28.2 oz-in off-the-shelf flywheel can be used
without needing to be match balanced to the previous flywheel.

Dan Jones
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