Help!! Need advice??
Thread Starter
Racer
Joined: Dec 2000
Posts: 422
Likes: 0
From: Mesa AZ
Help!! Need advice??
I just got my car back together with a new 383 and fourspeed conversion. I just realized that I may have made a mistake. I bought a flywheel and tranny from a friend pulled from 427 for a 6spd conversion. I installed them on the 383 and just realized that I may have needed to get a different flywheel as the 383 should be externally balanced and the 427 was internally balanced, am I right?? 
Am I right? What is the consequence of driving it this way? Should I cease and desist immediately? Is there anyway to add balance weights without tearing it all down again?
Am I right? What is the consequence of driving it this way? Should I cease and desist immediately? Is there anyway to add balance weights without tearing it all down again?
Melting Slicks
Joined: Apr 1999
Posts: 2,010
Likes: 3
From: Moon Twp. PA USA
Originally Posted by chadman
I just got my car back together with a new 383 and fourspeed conversion. I just realized that I may have made a mistake. I bought a flywheel and tranny from a friend pulled from 427 for a 6spd conversion. I installed them on the 383 and just realized that I may have needed to get a different flywheel as the 383 should be externally balanced and the 427 was internally balanced, am I right?? Am I right? What is the consequence of driving it this way? Should I cease and desist immediately? Is there anyway to add balance weights without tearing it all down again?
Am I right? What is the consequence of driving it this way? Should I cease and desist immediately? Is there anyway to add balance weights without tearing it all down again?If it is indeed an external balance unit, you have to use the external balance flywheel and dampner.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
If you used a 400 GM crank you've made a mistake, both on the flywheel and probably the harmonic balancer (damper) which is also weighted for the 400 crank,...the block didn't allow enough room for counter weights so GM added weight those two parts.
But, most aftermarket cranks are internally balanced.
Have you run the engine? If you mismatced parts, I'd imagine you're engine would run mad with vibration.
Let us know.
But, most aftermarket cranks are internally balanced.
Have you run the engine? If you mismatced parts, I'd imagine you're engine would run mad with vibration.
Let us know.
Thread Starter
Racer
Joined: Dec 2000
Posts: 422
Likes: 0
From: Mesa AZ
It doesn't vibrate badly but at highway speed I feel a vibration similar to wheel balance vibration. When I bought the motor it had a weighted flexplate. It just didn't dawn on me when I picked up the flywheel that I would have a problem. I'm pretty sure that I need to add the weighted flywheel or experience eventual damage. How sever should the vibration be? I'm sure the builder had the correct harmonic balancer on and I left it on. Unfortunately I bought it 2 1/2 yrs ago and can't contact the builder. 
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Since the imbalance is centrifugal, it will get worse as engine speed rises. Do not take imbalance like this lightly. It may be tolerable or not even all that noticeable at low rpm but it is doing damage. In a cast crank engine, you will eventually crack the crank. But it will probably take out the main bearings and the transmission before you get that far.
Most 383 conversions use either a full external balance or a version of a Detroit balance (weighted flywheel, neutral damper). An internal balance is an extra cost option that you have to ask for.
Most 383 conversions use either a full external balance or a version of a Detroit balance (weighted flywheel, neutral damper). An internal balance is an extra cost option that you have to ask for.
Thread Starter
Racer
Joined: Dec 2000
Posts: 422
Likes: 0
From: Mesa AZ
OK, I pulled the flywheel and it is not a neutral balance for a 427 as I was led to believe, it was counter balanced for a 454. Took it to a machine shop to have it rebalanced for the 400 crank. The 454 required more counter weight than the 400. I guess the reason my vibration was not too bad was that it was over weighted instead of not weighted at all. I don't know how long it would have taken for damage but I'm glad I decided to check it out. Can't wait to get it back together and see how much difference I see. 
