Ok, so I'm new on here so forgive me for any confusion.
I have a 1986 z28 305, 4 barrel carb, 5 speed manual. My block ended up getting cracked and poured coolant out the sides. I pulled the 350 out of a 1988 Silverado throttle body injection automatic, rebuilt it with new bearings rings, seals, re-seated/faced the valves and mild cam intake and headers. Keeping it carbureted . . . Strict budget at the time. My 86 305 had 2 piece rear main seal, 88 as you can guess, one piece rear seal and after tearing apart found that It has 4 bolt mains and the cylinders are bored .030, so it's about 355ci? I've read a lot about 86- up being one piece seals and being externally balanced, everything prior being internally balanced, and other things I've read are that only 400 small blocks are externally balanced due to the fly weights needing to clear the bottom of pistons at BDC. My question is. . . Is it ok to use my 86 2 PIECE Rear main seal 305ci manual fly wheel on the 1988 350 ci one piece rear main seal? Will it vibrate badly, possibly damage the crank and bearings?

 

I believe it won't bolt on. Just find a one piece style flywheel. All one piece rear main cranks were internally balanced.

 

It bolted up fine, clutch and trans are all together, had to use the starter from the 305 due to it being a smaller flywheel. Only ran the engine once since the rebuild, with the original flywheel and starter but that was for auto trans. Just put a new torque arm and cross member in, haven't ran it yet but don't want to damage the crank if it's the wrong balanced flywheel.

 

I don't think it'll be out of balance, 305s were internally balanced as well.

 

I didn't think so either but so many people say there's a difference between one and two piece rear seals. I plan on getting a new harmonic balancer when the clutch is ready to be changed, unsure if I should buy one for int. Or ext. Probably wouldn't be a while since I rarely use the clutch other than quick shifts and dead stops. Thanks for your input, everything helps

 

86 should have had a 1-pc rear main seal motor. That was the 1st year of that.

As such, its flywheel will bolt to other 1-pc motors including 88, and the balance will be the same... INTERNAL balance, with the rearmost bit of INTERNAL weight mounted on the flywheel.

The ONLY externally balanced small block motor is the 400. All others are INTERNALLY balanced.

If you had a flywheel for a 2-pc RMS motor, it would not bolt to a 1-pc motor AT ALL; not even close. The bolt pattern is SO DIFFERENT you'd laugh at how wrong it would be. Balance would not even be an issue.

Since ALL 305s and 350s are INTERNALLY balanced, you can buy a crank damper for ANY 305 or 350, and it will have the correct balance. There are other issues that may appear, such as timing mark location, diameter, etc.; but balance won't be a problem.