Engine balance ?

[GBGN1]

So I have a BA Stroker crank, SFI flywheel(no weight) and a modified front hub/balance machined for neutral balance. All matching componants.

Do these still have to be balanced together before they go into the block?

 

[turbodave231]

Yes, Just like buying new wheels and tires. They don't come pre-balanced. You must have the components balanced.

You will need to supply the pistons, rings, pins, locks, rod bearings, con rods and crank to the machinist who is doing the work. He will weight match the components, calculate a bob weight then balance the crank with special "bob" weights attached. It wouldn't hurt to have him check the flywheel and balancer while he is doing the work.

You will want to use a 36.6% balance factor for the balance job if this is a street car.

 

[GBGN1]

Thanks for the info and its exactly what I was thinking. Just didnt know of the 36.6 balance factor

 

[STP]

Why 36.6%, Dave? Why not 50% if he can get away with it? This is something I haven't ever fully understood...Seems to me like you would want it balanced as high as you can get away with. Unless his combination of parts are so heavy balancing to 50% would require mallory.

 

[turbodave231]

36.6% balance factor is recommended in the Buick Motorsports manual when used with flexible engine mounting because 36.6% bf keeps the imbalance in a horizontal plane. Every 50% BF job I've ever done requires a couple slugs of heavy metal in the crank. 50% bf gets expensive and not recommended for a street car.

 

[STP]

I guess it depends on the weights of his pistons/pins/etc...I just finished a 109 stroker for a guy a few months ago. Had it balanced to 50% and it's the smoothest one I've assembled to date. Hence the reason for my question...I've always heard 36.6% was fine, but I can tell a difference. Have another one at the machine shop now that should go 46% without any slugs...Should I let him do it or drop back to 36.6%?

 

[750H.P.V6]

You can use a balance percentage anywhere between 36.6% and 50% and it will work. It's a trade off between horizontal and vertical imbalance. 50% works best with solid mounts but will be much smoother with poly type mounts also as they transmit more engine vibration than the OEM rubber mounts do. If you can balance your motor at 46% without adding heavy metal I'd say do it. I've balanced a few between 42 and 45% and it works fine.

Neal