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Discussion Starter #1
I have owned this car (69Z28 with a 302) for 36 years and the engine has had a small vibration in it ever since. I noticed the vibration when I first bought it in 1978 but I did some street racing with it anyway. I have recently finished a complete restoration and now I'm focusing in on the vibration. With the car not moving, I can feel the vibration when I race the engine to maybe 3000 rpm with the clutch engaged or in neutral and the clutch disengaged. I'm a steel fabricator by trade and not a mechanic. Could the problem be the flywheel or the harmonic balancer. Please advise.
 

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I have pulled the balancer off and run motor without it, just to verify what you are saying, it was not that . You may have something on the clutch/flywheel end. I would start there.
Sure its not a miss? Fan clutch? Water pump? You can pull the belts off to eliminate these momentarily to try and isolate.
 

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Discussion Starter #3
Thanks Don,
My painter is touching up some of my assembly mistakes so it will be about 3-weeks before I get it back. I'll try removing the fan belt first.
 

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I agree,..the problem is likely with the pressure plate and/or flywheel. Take them both (with the the PP bolts) to your machine shop. Have them zero balance both (neutral balance). Also, he'll put a mark on both parts showing where the 12 o'clock mounting was when balanced and where it should be when mounted. Even with the correct 'shouldered' bolts, there's enough slop to cause issues. You'll likely have to turn the crank by hand to make sure the "7th' holes match up on the crank flange and flywheel so that you can obtain the 12 o'clock position.

Good luck!
 

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You say clutch engaged and not engaged. Was it in gear so the clutch plate was not spinning with the pressure plate?
 

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Have you studied the engine as someone revs it ?

You might see a bent pulley or the engine might move as the engine revs (bad motor mounts).

Watch the harmonic damper as the engine revs.

Start with the easy things first. The chance of it being an engine balance problem is very small.
 

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Discussion Starter #9
Thanks guys,
I feel much better now. I thought my problem was with the engine. I don't remember when I changed the pressure plate and disc. they both look pretty good.
 

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Motor was neutral balanced by GM to half an ounce (about 16 grams). Most competition race engines are balanced to within half to a full gram of dynamic weight.

Neutral balance means everything you bolt on the engine shouldn't affect the balance as they are also statically balanced. The problem arises from the fact that not everything is balanced to the tightest of tolerances to begin with and tolerances can add up.

By that I mean an engine started out with a tolerance of ± 8 grams. You then add to this the tolerance of about ±5 grams that most aftermarket parts are balanced to and you can one part zigging while the other is sagging. That is to say the fly wheel has a locator pin, as dos the harmonic balancer that slides onto a Woodruff key, this doesn't imply that the part is balanced at that location. The point at which the weight was removed (drilled) can be anywhere on the perimeter of the part. Because of this a part that is in balance ±the tolerance allowed can be off at one point that much. Add another part that is also off at that point and the out of balance condition can get worse.

The factory and the aftermarket industry rely upon statistics (the law of averages) to protect themselves from an engine being out of balance by something being bolted to it. Racers that have to spin to the moon rely upon balancing everything from blower pulleys and fuel pumps to flywheels or flex plates being balanced as a unit at one time. Once everything has been balanced and the weights recorded you can get any replacement part balanced to the at weight as the locator pin or key way hasn't moved.

Abnormal clutch wear (or part of the friction surface breaking off) can unbalance an engine. A pressure plate that has lost a balance weight (they clip on as opposed to boring holes in the cover or on the friction surface) can come off with time and will be out of balance as well.

Usually these posts are the result of drive line vibrations caused by drive shaft phase angles, pinion off set or just loosing the balance weight that is only good to 5000 RPM on the drive shaft which is locked to the motor at one to one in forth gear. So if you were buzzing your 302 through the lights the drive shaft could be putting a lot of wear on bearings and seals even though you may not have the time or interest to even notice as you go through the lights.

The only other source of a vibration in the motor could be a bent crank but that usually shows up as a drop in oil pressure as the bearings are swedged apart by a bent crank rotating. I favor the clutch and pressure plate first, a bent pulley or worn out fan belt missing chunks a distant second.

Larger Dave
 

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Discussion Starter #11
Thanks dave,
I appreciate that information.
You never get to old to learn something.
 

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The 327 in my Camaro was nice and smooth before I had a local shop rebuild it. They bored it .030 over, turned the crank, and balanced the rotating assembly. When I put it back together it had an engine vibration. The vibration was especially bad at 3000 RPM. This is right at 70 MPH with the rear end gears I have.

Driving around town the vibration was hardly noticeable. A long trip on the freeway was an entirely different matter. The vibration made the car noisy and unpleasant to be in.

First I removed all the fan belts to check if the problem was with one of the accessories. Next I installed a new clutch, flywheel, and balancer. The vibration was still there.

A few years ago I was planning a 500+ mile trip in the Camaro. A month before the trip I made up my mind I was going to fix it. I pulled the engine and took the rotating assemble to another machine shop to have it balanced. This shop got it right and the engine is now nice and smooth and the car is a pleasure to drive. It was well worth the effort.
 

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The 327 in my Camaro was nice and smooth before I had a local shop rebuild it. They bored it .030 over, turned the crank, and balanced the rotating assembly. When I put it back together it had an engine vibration. The vibration was especially bad at 3000 RPM. This is right at 70 MPH with the rear end gears I have.

Driving around town the vibration was hardly noticeable. A long trip on the freeway was an entirely different matter. The vibration made the car noisy and unpleasant to be in.

First I removed all the fan belts to check if the problem was with one of the accessories. Next I installed a new clutch, flywheel, and balancer. The vibration was still there.

A few years ago I was planning a 500+ mile trip in the Camaro. A month before the trip I made up my mind I was going to fix it. I pulled the engine and took the rotating assemble to another machine shop to have it balanced. This shop got it right and the engine is now nice and smooth and the car is a pleasure to drive. It was well worth the effort.
If the second shop gave you a "bob weight card" , listing what all was balanced to , keep it .
Possible they found the problem within the fly to clutch area.
 

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Discussion Starter #14
I was thinking about testing myself to see if the pressure plate/disc was the cause of the vibration. Could I support the back of the engine and remove the transmission and bell housing. Then start the engine and see if it vibration is there with the pressure plate/disc and without pressure plate/disc.
 

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I was thinking about testing myself to see if the pressure plate/disc was the cause of the vibration. Could I support the back of the engine and remove the transmission and bell housing. Then start the engine and see if it vibration is there with the pressure plate/disc and without pressure plate/disc.
I have done this, You can by supporting oil pan with say a 2 x8" block of wood on small jack, what ever fits pan better. CAUTION, stay away from the rotating flywheel.
I presume you will be doing this with car on jack stands?
 

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You know that sounds like a possibility. I hate running an engine like that but have done it. I have not run back through the thread, but have you replaced the pilot bushing? Theoretically, if the bushing is worn enough, the pressure plate could clamp the clutch plate off center and cause the vibration even if all parts are balanced while on center.
 

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I too have removed the pressure plate to see if it would remove an out-of-balance issue. But, obviously, you can't start her her without the flywheel so the only way to test the flywheel is to take it off then take it to your machine shop for balancing.

Again, you'll take the FW and pressure plate and have them balanced together so when bolted together for balancing you'll know the 12 o'clock position to be used when you mount them to your crank. Again, even with the correct shoulder'd bolts the PP can sit in a slightly 'off' position unless you do it this way.

Lastly, as much as we all like to think new parts are properly balanced, you'd be wrong, sadly. I'll never mount a flywheel or PP without having it balanced prior.

Good luck!
 

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Agree with Scott and Inline, While clutch and pplate are out , might just replace that pilot bushing to be safe. Use a GM bushing or you can get a Federal Mogul PB-656HD from Napa. Normally they have them. These are bronze/alloy bushing , no iron. Put a magnet to it if you are not sure.

Balancing the entire rotating mass is a good idea. Used to do that on every balance job I had done.
Hope you find something.
 

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Discussion Starter #19
Thanks for the response. I think I'll buy a new clutch assy and take it and the flywheel to a machine shop for balancing.
 

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Thanks for the response. I think I'll buy a new clutch assy and take it and the flywheel to a machine shop for balancing.
Still need to see if there is any vibs without anything on flywheel. I prefer billet flywheels if I had to replace a cast iron. Its the heaviest part and give me piece of mind it will not take my foot off as I now longer run scatter shields .
 
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