One More Fly Wheel Question.

[mattpiotr]

I picked up a new flywheel today with sfi spec. i got home and matched it up with the old one and noticed that there is no balance on the new fly wheel. it is going on a 86 GMC 2500 350 motor with a turbo 400 transmission. the original one i changed out of the truck has a balance on it tho. could that be the problem why the flywheel cracked? or do i have the wrong replacement one?

[ray_mcavoy]

Does your 350 have a 1 or 2 piece rear main seal?

If it's the truck's original engine then I believe it will be the 1 piece seal (I think 86 was the first year). And the flexplates for the 1-piece rear main seal 350's do have a counterweight on them. It takes the place of the counterweight that used to be part of the flywheel/flexplate mounting flange on the older 2-piece rear main seal crankshafts.

It sounds as though you might have the wrong replacement part. As an additional check, compare the bolt patterns on your old vs. new flexplates. The flexplates for 1-piece rear main seal engines have a smaller hole in the center & smaller bolt circle where they bolt onto the crankshaft.

[mattpiotr]

Originally Posted by ray_mcavoy

Does your 350 have a 1 or 2 piece rear main seal?

If it's the truck's original engine then I believe it will be the 1 piece seal (I think 86 was the first year). And the flexplates for the 1-piece rear main seal 350's do have a counterweight on them. It takes the place of the counterweight that used to be part of the flywheel/flexplate mounting flange on the older 2-piece rear main seal crankshafts.

It sounds as though you might have the wrong replacement part. As an additional check, compare the bolt patterns on your old vs. new flexplates. The flexplates for 1-piece rear main seal engines have a smaller hole in the center & smaller bolt circle where they bolt onto the crankshaft.

Well the truck does have a 1 piece rear main seal. the bolt patterns all line up with the old up. The only thing is the one i picked up is not a replacement part. its supposed to be a heavy duty flexplate made by sfi with racing specs. could it be with it being a heavier flexplate that it balances its self off?

[ray_mcavoy]

I replied to this in your PM as well, but figured I'd post it here too so everyone else can read it.

The fact that the bolt patterns match up is a good sign. I'd still be concerned about the lack of a counterweight though.

I know the stock flexplates all had that counterweight on the 1-piece seal applications but I'm guessing that the aftermarket HD flexplates might be available both ways (with & without) the counterweight. And ones without the counterweight would be meant for use on modified engines that have had balance work done to the crankshaft in order to eliminate the need for that weight.

[mattpiotr]

Also as i got to thinking tonight this is the 3rd time I've had to change the flex-plate on this truck, every time it starts off with the bolts from the flex-plate to the torque converter coming loose and i get that sound so i tighten them up thinking that they were just loose up but in reality its already cracked. and over time its just cracks more and gets worse. i am wondering if maybe i do need a flex plate with out the balanced weight, everyone i've replaced with is one with the balanced weight

[ray_mcavoy]

Did the engine run smooth with the previous counterweighted flexplates? If so, I think you'll want to stay with that style and look elsewhere for the cause of the loosening torque converter bolts (maybe a problem with the torque converter itself, dowel pins not correctly aligning engine & trans, etc ...)

But if the engine had vibration issues with the previous flexplates then you might indeed need the one without a counterweight. Do you know if the engine has any modifications (like a stroker crankshaft or something) that would change the balancing?