cloudshe

'65 roadster, ex-L76 solid lifter m21 3.73 now sp383 autogear m20 3.08. getting noticeable vibration starts at 1300R to 1700R no change in/out of gear, clutch in or out. put in recommended flywheel for ext balanced gm SP383. any suggestions?

phil2302

Have you tried replicating it in the garage pushing throttle by hand and listening feeling etc.
Prob need to get it on a lift and run it at problem rpm range.

Plasticman

What is "SP"?


If External, are you using the correct offset balanced balancer?

I see that you say you are using "correct" externally balanced flywheel, but where did the engine come from, and how do you know it was externally balanced?

65tripleblack

What was on the rotating assembly when it was balanced by the builder?

MikeM

In addition to this question, did you have the new(?) pressure plate balanced?

wmf62

sounds like a GM crate engine

Bill

kellsdad

Here are the specs: SP383 . It is externally balanced. .... You may want to put the flywheel # for the skeptics.

MikeM

Is it a buzz or a shake?

Could be the exhaust is grounded to the frame.

cloudshe

SP383 is a recent upgrade to the GM SBC crate motor stroked to 383, i think the previous motor was designated ZZ383. google gm sp383 for more info. thanks for your interest in my gripe!

cloudshe

the bell housing & clutch assy came off the previous smooth running 327/350 (orig block had been replaced). i was hoping to find someone on the Forum who might have had a similar problem, where the rpm range was indicative of what was out of balance. thanks for yr interest!

kellsdad

I'm a novice at this stuff myself, so I'll pose my idea as a question. Did you check the alignment between the new engine and the old bellhousing? And could misalignment cause the vibration symptom?

wmf62

"I" don't think so, you would feel it in the transmission, not the engine

Bill

MikeM

That is why I asked if your vibration was a buzz or a shake.

6T7L71CPE

I had a remanufactured alternator cause a similar vibration years ago. I believe it was the poorly made pulley. Try removing all belts to see if the alternator or other accessories may be the cause.

cloudshe

yes, i was thinking that too. i'll have to ask the guy who put it together, he had a lot of faith in the GM product, and i had no problems with the old bell housing fm 1965. would probably be worth checking out, even though there was no difference in the vibe clutch in or out, in gear or not. thanks for the suggestion!

65tripleblack

With externally balanced engines, both the flywheel and damper have to be be mounted on the crank prior to balancing. If the builder balanced the assembly with only the damper installed then a zero balanced flywheel is needed. Clutch pressure plates are zero balanced.

kellsdad

I started a new thread to discuss this.

Per the new thread, the above statement may be true for a custom built engine, but is not required for the SP383 crate engine used by the OP. As long as he used the correct externally balanced flywheel it should work OK.

cloudshe

i hate to think i would have to send the crate motor back to GM and hope the replacement didn't have the same problem! am wondering if that RPM range (1300 - 1700) is indicative of a flywheel or balancer or crank or missmatched piston or whatever. i'll talk to the installer, a 35yr expert on vette restoration, see what he thinks. he says the best thing about using the GM product is that they're easy to work with. appreciate your reply!!

68hemi

Ha Ha!

You need to talk to some of the guys that have bought these engines and some of the other modern engine to put in their resto mods. They take the engine to their Chevy dealer for warranty work and they turn them away because the don't have equipment to work on them in the old cars.

cloudshe

i guess i wasn't very clear, my resto guy does the work, the GM vendor supplies the parts under warranty. he says he doesn't like to install motors fm independent builders because they don't always honor their promises