Engine Vibration help/ideas
Thread Starter
Heel & Toe
Joined: Jun 2007
Posts: 16
Likes: 0
Engine Vibration help/ideas
I have a 70 Corvette, 454, manual trans with a vibration that seems to be from the engine. The vibration starts in about 2100 rpm and ends above 2600 rpm. The vibration occurs moving in all gears, or standing still. Standing still it occurs with the car in neutral, clutch out, or in gear with the clutch pushed in. The last case takes everything out of the equation except the engine, pressure plate and accessories. The engine was rebuilt some time ago and supposedly the internals were balanced at that time. I believe the vibration damper was replaced at that time also, but I don't remember for sure (it has been many years ago). I have tried looking at the engine while it is running at the rpm in question, but don't see anything shaking. This is not a serious vibration, but it is noticeable, and is something I have always wondered about, and would like to fix if possible. Could a defective vibration damper do this? Any ideas would be appreciated.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
IF this just started, I'd look at the balancer and see if it is failing and has slipped. IF not, what was the last thing done to the engine before it started? Try removing the belts and running it. IT could be the fan or an accessory too.
Drifting
Joined: Mar 2011
Posts: 1,347
Likes: 121
From: Kernersville NC
Always wondered about? When I replaced the clutch in mine I found that the pressure plate did not have shouldered bolts. The slight vibration I had went away when the correct bolts were installed and the pressure plate was centered up correctly.
Pro
Joined: Feb 2017
Posts: 518
Likes: 365
From: San Diego
2023 C3 of the Year Finalist - Modified
If the problem has been there forever it is probably not this but my previous vibration issues on other vehicles always turned out to be motor mount related. It might be worth taking a peek at yours.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The source of that vibration is in one of the following:
1. the engine itself....moving components balance problem;
2. the vibration damper at the front of the crank;
3. the radiator fan;
4. one (or more) of the components driven by fan belts;
5. the pressure plate/clutch (not centered).
You can eliminate #3 and #4 by removing all of the drive belts and revving the engine to see if the vibration is still there. Running the engine for a minute or so without the water pump running is no big deal.
There is no good way to separate out the potential problems with the damper, the clutch, nor the internal balance. But, thinking about WHEN this became a problem my help eliminate one or more of those items. If the vibration wasn't a problem before you did some specific work on the engine, use that as a clue. Likewise, if the vibration REMAINED after doing some specific work on the engine, that would also be a useful clue toward diagnosing the problem source.
1. the engine itself....moving components balance problem;
2. the vibration damper at the front of the crank;
3. the radiator fan;
4. one (or more) of the components driven by fan belts;
5. the pressure plate/clutch (not centered).
You can eliminate #3 and #4 by removing all of the drive belts and revving the engine to see if the vibration is still there. Running the engine for a minute or so without the water pump running is no big deal.
There is no good way to separate out the potential problems with the damper, the clutch, nor the internal balance. But, thinking about WHEN this became a problem my help eliminate one or more of those items. If the vibration wasn't a problem before you did some specific work on the engine, use that as a clue. Likewise, if the vibration REMAINED after doing some specific work on the engine, that would also be a useful clue toward diagnosing the problem source.
Drifting
Joined: Apr 2008
Posts: 1,540
Likes: 51
From: Lexington Park Maryland
If the motor has been rebuilt before you owned it..., and it's always done it since you've owned it, maybe the wrong balancer (or flywheel) was used ? 454s are externally balanced motors (vice internally balanced 396s and 427s). Just a thought.... 
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
My bet is on a non-centered pressure plate and disc. It doesn't have to be off much to make a lot of vibration.
Defective or wrong damper would be my second choice.
Defective or wrong damper would be my second choice.
Last edited by 7T1vette; Jul 7, 2017 at 12:50 AM.
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