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markiemyster 07-29-2003 08:34 PM

wrong flywheel
I was having a vibration problem in my car and after several opinions from people that didn't seem to be the problem I decided to take it to the local hotrod guru. I told him to go throug the car and fix whatever he thinks needed fixing.
The first thing he noticed was the engine is a 350cid and the flywheel was a 400 flywheel. He purchased the correct one and will install it when he gets it in from Summit. He never explained to me what happens if the flywheel is incorrect.
Can someone tell me what happens in this case? Does the engine wear out? Is it unbalanced? did I do any harm to the engine by driving it this way for 2000 miles.
It was that way when I bought it.
Thanks, Mark

woodz428 07-29-2003 08:41 PM

400's have a balance weight on the flywheel that the other smallblocks don't have and that would indeed create a vibration. Now that I've said that somebody may say that the later 350's have one too.:D

markiemyster 07-30-2003 06:01 AM

The 350 is out of a 1984 pickup truck if that explains anything.

Biggarmike 07-30-2003 08:06 AM

I had a similar occurence a few years ago, I bought a 350 11" flywheel from a buddy, a GM guru, hung it onto my 327, and had tons of vibration, since I had built the motor from the bottom up with scrounged parts to get a numbers match, everything was suspect. I finally found the problem to be the flywheel. It was a 350 flywheel allright, (internally balanced) but someone had balanced it to a 400 by drilling it to work as an externally balanced one, then hid the handywork with black RTV. TALK ABOUT BENT OUT OF SHAPE! Anyway, I'll never neglect to balance the rotating assembly again, for any reason!

11echo 07-30-2003 08:20 AM

Small block Chevy's are internally balanced, and big block Chevy's are externally balanced (they have the weight on the flex plate). I had this problem a number of years ago. Got a small block flex plate behind my 454. The mechanics noticed "something" was wrong but didn't know what. I had built the engine and had laid the crank flat on the ground for sometime. I was worried I had warped the crank. I talked with a master engine builder later and he asked me if I had the "weight" on the flex plate. I checked and it wasn't there wrong plate! Damn thing vibrated my water pump off! *G* That was fun!
400's are kind of an odd ball engine, they are configured after a small big, but are externally balanced like big blocks. NOW I'm not a 100% on this advise, but it's a starting point for you to check on. GOOD LUCK! ...Mark

78 monte 07-30-2003 01:53 PM

We had that problem on a 327 it vibrated so bad it cracked the bellhousing on the tranny.
We zinged the weights off with a torch and it worked.

MI2600 07-30-2003 03:52 PM

I also had a problem with my 383. At first, I had a 350 flywheel drilled to balance as a 400...vibration. Then I tried one of those "balance plates" that you put between a 350 wheel and the crank...vibration. I finally put an actual 400 flywheel vibration. I guess you get what you pay for.

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