This project has been nothing but a disaster since I started
I had machine shop stroke my 454 to 496. Balanced assembled everything. I did not want to take a chance of any more problems.
SO here goes.
It started right up. But as soon as you give it gas past 1,200 RPMS it VIBRATES so bad I you have to shut it down. It idles fine but as soon as you give it gas the vibrations starts. I have only ran the engine for 3-4 minutes.

ANY IDEAS??

The only thing that comes to mind is valves hitting pistons I used the same cam as the prev engine, nothing special 540 lift. I did not check valve to piston clearence because its never been an issue. There was a huge relief for the exhaust valve in the piston.
I checked spark plug wires twice when I installed them. I would not think the engine would idle if I had them mixed up.
Any comments??
Thanks
JIM

If the valves were hitting the pistons, it would not run well. What balancer & flywheel did you put on? New cranks are internal balanced. Old ones are external. Did you balance with the flywheel & balancer? Sounds like a balance problem

Check the simple things first.,
Engine will idle if wires are crossed!
1) firing order( Check again)
2) while engine is vibrating 1300rpm? Pull one plug wire at a
time while its running find the cylinder that does not
make a difference. this cylinder is the problem.
3) take a compression check of the above cylinder.
4) Whack the throttle if it backfires. Pull valve cover
on the suspected cylinder. Inspect rockers.



Dont Panic Its most likely simple.
Good luck
Gerry

First thing that comes to mind is balance. I did a automatic transmission for a guys blazer that had a 396,he called me up and said the transmiss ion was making it vibrate ,i looked at it for him and it turned out he put a 454 flywheel(externally balanced w/a big weight on it)on a internally balanced motor. It would vibrate progresively worse as you revved it like it was going to come apart.All stock 454 flywheels have the off balance external weight on them,if you re-used it and motor is internally balanced(which most stroker motors are) then thats your problem.If you need a zero balanced big block flywheel i have a regular one thats almost new for mk4 style crank as i put a billet race one on my motor this time,i'd take 75$ for it,Smitty

Seems to me that the pistons are installed backwards. The big valve relief is for the intake valve. If you have a cylinder head off and put the piston up to the head, you will see what I mean. A 454 is externally balanced, if the stroker crank is internally balanced (most custom crankshafts are) then you will need a internal/neutral balance flywheel and harmonic balancer.

When I built my 540s (same stroke as a 496) I had to machine off the weight on the back of the flywheel. If the shop balanced your internal crank with out the flywheel on , that's the problem.

Its an external balance application. I don't think it can be a balance issue. Yes everything was balanced at the machine shop. The valve relief is always exhaust and always goes to the right. I have been doing this for 30 years but my first stroker moter.
This much vibration its something big.
JIM

Was there a alignment dowel in the crank for the flywheel? Crockett was telling me last month when i was there he had a customer put a flywheel on wrong bolts because of no dowel and motor was shaking itself to death,i though the bolt pattern was unsymetrical and that it wasn't possible but maybe?

If a valve was hitting it would have broke off and lunched the motor by now,most J/E and other pistons will take 650 lift without a clearence issue so it really can't be valve clearence,Smitty

On a Mark IV is it possible to bolt the flywhell on wrong? No there was no dowel pin. I would have to go look at my other crank because I don't think there is one there.