Engine balancing question

[JohnM]

Hello All,

My newly rebuilt 351W runs great. I am just now installing the clutch & preasure plate set up. When I noticed how heavy this is, I couldn't help but think of how my engine machinist balanced the crank with the harmonic balancer and a weighted flywheel. Can anyone tell me why, with all that added weight now being attached to the flywheel it would seem that the engine should now be way out of balance. Is the added weight of the clutch and pressure plate outside of the balancing"envelope" and does not become a factor?

I just found it interesting and something else to ponder.

Thanks

John

[Ikestaa]

I am by no means an expert, but I'm pretty sure the clutch and pressure plate are balanced at the factory. When you combine a balanced motor with a balanced clutch and pressure plate you get a balanced assembly. Not really sure at all, but that would be my guess.

[bly]

when i had my 351w built, the machine shop balanced the flywheel ,pressure plate along with the rest of rotating assembly.

[Mr.Fixit]

The flywheel needs to be in place to balance a 351w. It has a big weight hanging out at the outer edge which is necessary since it's an externally balanced engine, same goes for the dampner. The pressure plate is supposed to be neutral balance, so that it can be replaced without tearing the motor apart to redo the balance job. We always balanced the rotating assembly, then bolted on the pressure plate and corrected it's "neutral" balance. They didn't all need correction, but at 7500rpm, a little shake turns into a big shake.

[JohnM]

Hello All,

I called my engine machinists...who said the same thing Mr. Fixit said. If you balanced the presure plate and clutch with the whole assembly, then you would have to rebalance everyrtime when you canged your clutch. Since my engine will always stay (hopefully!!) on the short side of 6000rpm.... the from the factory neutral balance is OK.

Thanks for the feed back

John

[Paul Rose]

I've always heard that clutch discs are balanced, but that you shouldn't count on pressure plates.

An article on FordMuscle.com recommends that you bring along your pressure plate when you have your engine balanced. Of course this doesn't do you much good if you have to replace your pressure plate later...

EDIT: nevermind, I just read Mr. Fixit's reply more closely. That makes sense. Balance w/o pressure plate, then "fix" the balance of the pressure plate.

[flipper35]

On an externally balanced engine why don't they take the weight off of the opposite side instead of putting the weight on ?

[My427stang]

We neutral balanced the flywheel and the clutch assembly (first the flywheel, then the assembly), then balanced the motor with the assembly and did all the final work on the crank.

It was a lot of extra work, but the purpose was to make the clutch and flywheel true zero balanced so that at a later date I could go with an alum flywheel and a different clutch and only have to balance those pieces to true zero before bolting it on

[DAVID GAGNARD]

I posed that very same question to a shop here a year ago. This is what they do and it sounds right to me----Balance the rotating assy as one unit (harmonic balancer-crank-rod weights,piston weights with rings and inserts-and flywheel) this is balalnced as one unit....then he balalnces you pressure plate and clutch to zero balance and marks the location of the clutch to pressure plate....takes more time and only charges $25.00 more,but later on you just hang a new clutch and pressure plate on without messing up your engine balance,or bring him the new pressure plate and clutch and for $25.00 he will balance them seperately to zero balance....

David