Externally balanced engine troubles
 

Hi all,
Started my rebuilt 454 (Originally out of a '78 chevy pickup) for the first time today and found that it has a fairly violent shake that increases with engine speed. The only thing I can think of is that the PO put an internally balanced fex plate and harmonic balancer when they should be externally balanced pieces.So my questions are...
1. How can I tell for sure whether or not my flexplate/balancer are externally balanced?
2. Can I just buy an exterally balanced harmonic balancer/flex plate and install them? Or will I need to get the whole rotating assembly balanced as well?
Thanks in advance for amy help
-Jordan

Re: Externally balanced engine troubles
 

The balancer has a weight that is inside the hub and extends nearly halfway around it. I think you can feel it inside the balancer from under the truck. The engine side of the flex plate has a flat plate welded to it you can see with the dust cover off. Google will show you some images on a search. The damper & flex plate aren't balanced to a specific engine so you can put them on your shakin' engine if that's the problem. GOOD LUCK!!

Re: Externally balanced engine troubles
 

Thank you sir! That's exactly what I needed to know. After a quick stop at the parts store I have what I need for under $100. That's MUCH less than I figured this vibration was going to cost me.

Re: Externally balanced engine troubles
 

When we put our 396 back together and started it up, it had a very bad vibration. We thought the machine shop screwed up the engine. He told us to make sure the flex plate was installed right. We thought the flex plate can only go on one way. When you spin the plate with out the bolts on the back of the crank, the bolt holes can only line up one way. We were wrong. The flex plate bolt holes were off 180 degrees. We spun the flex plate 180 degrees (one half turn) and the bolt holes lined up again. We bolted it up and started the engine and it ran smoothly with no vibration.

Re: Externally balanced engine troubles
 

ballencer will have a cavity on the back side of the ring
http://i20.ebayimg.com/02/i/02/0f/bc/3c_1.JPG
flexplate will have a weight welded to it
http://i.ebayimg.com/t/BBC-Chevy-454...v)w~~60_12.JPG

Re: Externally balanced engine troubles
 

If it's an automatic it's easy to put the flexplate on backwards, which would cause it to be wildly out of balance. Just a thought.