351W Swap Question

[broncomanbrad]

My brother is in the middle of doing a swap from his stock 302 to an '84 351W. He apparently had the 302 flywheel on the 351 and it is creating a lot of vibration. My dad and I (bro's not at home) are wondering whether the balance would be off and create the nasty vibrating or would it be something else?

 

[bax]

if you take internally ballanced engine parts ( Dampner or flywheel ) and try to swap them to an externally balanced engine or vice versa that engine will shake like crazy. However I dont know how the 302 or the 351 are set up.

 

[JWMcCrary]

Later model 302's use a 50 oz flywheel and balancer...all 351W's (unless custom balanced by a machine shop) use a 28 oz flywheel and balancer.

 

[broncnaz]

As long as his stock 302 was a pre 1982 engine then the flywheel should be correct of a 351W. I would check the harmonic balancer it may have slipped and is causing the vibration also the clutch itself could be a problem especailly if its one of the El Cheapo brands.

 

[SecondChance]

Early 302 is 28 oz balance on the flywheel so it depends if you pulled a late or early 302 out.

 

[broncomanbrad]

Thanks for the info guys. Right now my thoughts are on the clutch. He replaced it right before the swap.

 

[76Broncofromhell]

79.5 and later 302s have a 50 oz. imbalance. Small blocks were all externally balanced so that's not a concern either. My guess is you have the wrong firing order for the new camshaft which will make it vibrate badly at idle and have no power.