Long time reader and first time poster here, so be gentle lol. I have a 1955 Chevy truck with an earlier 2pc rear main 350 in it. It had a bum th350 in it so I swapped in a complete t5 setup from an 84z28. The z28 also had a 350 in it. I used the bellhousing, T5, flywheel, starter, clutch, etc all from the camaro. I've yet to drive the truck, but with the truck running in neutral I get a pretty good amount of vibration while free revving it. I was wondering t5 flywheel necessitates me to run a different harmonic balancer? From everything I've read I haven't seen anything about people having to swap balancers unless they are running a 400 crank. If you can't tell I don't know a whole lot about gen 1 sbc's. Is the 305 that this rig originally backed up internally balanced? How do I know if my motor is externally balanced? Sorry to come forth with so much ignorance here.

 

all sbc production are internally balanced except the 400 !

 

dit you remember to put the pilot bearing in the end of the crank shaft ?????????? sory to ruin your day.

 

Yeah I bought a spec stage 2 clutch for it. I put the pilot bearing that came with it in and reused the centerforce clutch that was in the camaro since my rear main is leaking a bit.

 

is the throughout bearing seated properly in the fork? could it be backwards ? SORY IF YOU THINK THESE ARE STUPID QUESTIONS.

 

Picture of the bellhousing? Under-car is fine.

 

the 86 and later engines with the 1 piece rear seals are externally balanced at the rear since they had to get rid of the counterweight at the end of the crank to allow for the seal, but still use the same neutral balance harmonic damper at the front.

regarding the problem posted by the OP: could be as simple as a couple of plug wires crossed... check the wires for 5 and 7, since they are not only next to each other on the engine but also in the firing order as well.. it's really easy to mix them up when putting the wires on, and the result is one cylinder that is firing about 45 degrees too soon and one that's firing 45 degrees too late..

 

The rear counterweight on the flywheel of an 86 is no different than the one on the back end of the 85 crank. It's not changed or "balanced"; it's a static part of the rotating assembly balance that's not changed. Both engines are balanced the exact same way. Internally.