'63 327/340 Engine Vibration above 3800 RPM

[Frederick H.]

Experiencing vibration that begins at 3,800 RPM and progresses up from there. The shop said low compression has been determined in #3 and #6 cylinders but everything else has been checked (drive train, timing, etc.). The vibration occurs whether driving or sitting still, in gear or in neutral. Two outside engine builders (one highly recommended engine builder from the shop and Corvette club and a local racing shop owner) have agreed that it is highly likely something internal. I'm digging for any possibility that it could be something else we've missed, as pulling the motor and doing an investigative rebuild is very expensive. The motor probably has less than a 1,000 miles on it but has sat a lot since it was put together back in the late 80's. I realize it could be a number of things internally - any ideas? I know I am going to want to go above 3,800 RPM every now and then .
Thanks in advance.

[Joe R.]

Re: '63 327/340 Engine Vibration above 3800 RPM

Frederick,

Check out the Thread below Engine Vibration Solved by Joe DeLuca. If your lucky that will fix your vibration also!

JR

[Terry D.]

Re: '63 327/340 Engine Vibration above 3800 RPM

You don't say how low the compression is. Besides checking flywheel have you checked the harmonic balancer? I would think if it is internal you would be hearing some noise, you don't mention any. Keep us posted.

[Duke W.]

Re: '63 327/340 Engine Vibration above 3800 RPM

The shop said low compression has been determined in #3 and #6 cylinders

How about giving us the actual numbers, and the details on "everything else has been checked"?

Has this vibration been apparent for the entire thousand miles since the rebuild, or ...?

You provided very little to go on.

Duke

[Frederick H.]

Re: '63 327/340 Engine Vibration above 3800 RPM

Yep - flywheel has been checked. Vibration occurs even when in neutral.

[Frederick H.]

Re: '63 327/340 Engine Vibration above 3800 RPM

I will have to refresh on the compression info. Shop says they have checked timing, flywheel, rear end. Vibration occurs when sitting and in neutral so drivetrain is not the issue. Car has not been driven much so I can't recall when vibration started. They did not mention harmonic balancer which I will ask about this week.

[Richard G.]

Re: '63 327/340 Engine Vibration above 3800 RPM

I agree with Duke, too little data.
More information is needed to determine if its a miss or some type of unbalance.
I would in general expect a unbalance issue to get worse as the RPM go up and a miss to be less noticeable.
A sound bite of the exhaust sound would add more data. Are the cylinders dead or just low? Even which cylinders are low compression would help.
Best of luck
Rick

[Frederick H.]

Re: '63 327/340 Engine Vibration above 3800 RPM

Understood - not a miss, shop says vibration tends to increase with RPM but didn't push it. Cylinders # & 6 are low as mentioned, but I will have to get with the shop on exact numbers (he told me but didn't jot it down).I can try to get him to rev it to the vibration point and record it whenever I get to the shop end of week. Sorry for the lack of info.

[Terry M.]

Re: '63 327/340 Engine Vibration above 3800 RPM

Frederick,
As others have noted, not enough information is provided. Hopefully, it might be a simple balancing fix as noted in the Joe DeLuca post. That said, it could be something more serious. You haven't reported anything on the engine rebuild (late 80's or 30+ yrs ago) details. What was done? What was the process? Who was the rebuilder? How reputable was the rebuilder?

If the engine was properly rebuilt and maintained, the compression in all cylinders should still be reasonably uniform. You could also do a leak down test which will help provide further insight as to ring and valve/seat sealing conditions. Oftentimes, engine rebuilding is not as thorough as it could be. The balance on flywheels, cranks and balancers is not always checked. In my view, they should be. If someone is going to go to the expense of rebuilding an engine, especially for a classic such as yours, they should not cut any corners. The added expense to do the things noted are not that great and are well worth the investment. In addition, was the crank checked for straightness and or reground? Failure to do so can be a possible cause for problems.

So, given the engine is really the heart of the car, especially an original engine, I believe a rebuild should be of the highest quality, done by a professional or, at least, using professional procedures. You'll never regret the expense or results. Good luck with your engine.

[Joe R.]

Re: '63 327/340 Engine Vibration above 3800 RPM

Yep - flywheel has been checked. Vibration occurs even when in neutral.

Fredrick, the flywheel goes round and round with the clutch disc and pressure plate even in neutral. When the motor is running all those things are in motion.

JR

[Frederick H.]

Re: '63 327/340 Engine Vibration above 3800 RPM

The engine rebuild in the '80's was a complete rebuild, .030 bore, balanced (no blueprint unfortunately). The current shop manager did a leak down test and said the two cylinders in question were low but I will have to get back with him for exact numbers. The rebuilder was in Kansas and had a good reputation. I can't tell you or remember the details of what went on last week much less 30 years ago. .
I apologize to all for starting this thread without have complete details - it has simply been too long and I think that's part of the problem -car was not driven regularly. The current rebuilder under consideration is well known and does everything to the letter - estimate is $4-5K depending on what he finds, not including cost to remove and install the motor. Thanks again for everyone's patience and support.
Fred

[Carl N.]

Re: '63 327/340 Engine Vibration above 3800 RPM

How old are your motor mounts ?? Sometimes it is the simple things that are overlooked

[Frederick H.]

Re: '63 327/340 Engine Vibration above 3800 RPM

Brand new.