Engine vibration

[Tony Radford]

I posted a little earlier that my car had developed a vibration that appears to be coming from somewhere north of the transmission. It feels as though there is an imbalance in the rotating assembly, so I immediately changed the harmonic damper (no effect). The vibration is very consistent and is very noticable during acceleration. She starts up fine and idles fine. The vibration is noticable when reving the motor at a stand still. My question - does it make sense that the problem could be with the ignition system? This problem started all of a sudden and following my washing her (including the engine). I'm running an MSD 6A system and distributor. The problem has persisted for the past couple of months, so you'd think any moisture would have evaporated by now. The only logical culprits remaining are something in the bellhousing getting out of balance, or something inside the motor. The nice weather is walking off and leaving me.

[trularin]

What did you do with the flywheel?

There would have to be a huge problem in a combustion chamber for it to rattle under fire. Like one cylinder has almost no compression. That would feel like a miss.

Is the vibration over the entire operating range of RPM or does it have a harmonic problem like vibrates at 2500 to 2700 then is smooth everywhere in between?

When you washed the engine, was it hot? Could you have fractured a weight in the flywheel or balancer that was flung off when it was started?

Just a few questions to get the thought process moving.

[master]

Tony, could it be something as simple as a universal joint on the drive shaft? When you push in the clutch is the vibration still noticable?

[Tony Radford]

No, it's certainly engine-related. With the driveshaft completely removed, the vibration is still there. The motor mounts were removed and checked as was the transmission mount. The vibration is present at all RPMs and is very consistent in frequency and amplitude. It feels very similar to the way it felt a few years ago when my pressure plate was installed without the alignment pins, only a bit worse. The concensus to date is that something in the bellhousing has become out of balance. It seemed a bit coincidental that the vibation first became noicable following a detailing. The engine was cold when I washed it. And I just rinse it with water (no pressure) as it's a polished motor. The flywheel and clutch assembly will go on the balancer next week. My MSD box is mounted inside the engine compartment on the firewall. Probably a long shot, but that's often where these gremlins live.

[Chilibit]

If it was ignition related then something this significant might show in a plug check. Are the belts running true? Is the vibration frequency less than RPM frequency?

[Clois Harlan]

Pop off your distributor cap and spray some brake cleaner in it and dry the inside out with a blue shop type paper towel. Your vibration could be some moisture in your distributor cap.

Clois

[Tony Radford]

Chilibit, the first thing I did (even before the harmonic damper) was change the plugs and the fuel filter (easy stuff first). It seems as though the harder I hammer it, the more intense the vibration is. When I back off of the throttle, it smooths out a bit. If you sit in the car and blip the throttle, you can feel the vibration. I'm running an aluminum flywheel, so you can feel everything. I just can't imagine anything mechanical that would cause this. The engine has been smooth as glass for that past 14K miles and "boom", here comes the vibration.

Clois, how long do you think moisture could remain in the distributor? After all, that was over a month ago.

[Speedysnake]

Tony,

I just reread this thread and it sure sounds like you're losing spark to one cylinder. Did you look at the plugs carefully when you replaced them?

Paul

[ENTDOC]

check the header temps with an IR thermometer,that is an easy way to check if one plug is not firing completely

[Tony Radford]

I did look at the plugs as I removed them and they were all a bit wet (welcome to the world of Barry Grant) and one in particular was extra nasty. My car is sitting down at Southern Automotive and I think they're going to start yanking parts next week. I'm going to ask Bill to check the ignition system first.

[TonyMadrid]

What about tthe motor mounts. If you use aftermarket stock mounts, they are usually made of rubber bonded to metal and due to the turning torque of the engine, one side can separate at the rubber and that can cause a vibration.

I changed mine and went with poly mounts. They cost about $100.00 but they won't separate.

[Rwillia4]

Sounds like a vacuum leak. You said it started after a washing and comes on stronger the harder you hammer it. I think you have a vacuum leak that is casing one (or more) cylinder to go lean and not fire. At idle you won't notice it when there is no "suck".

Do you have a break boost line? this would be the first line and fittings I would check.

[AK1234]

Flywheel ... Dont Forget You Have 428 Is External Balanced And 427 Internal Balance.

[351-EM]

Tony,

Any idea what caused/is causing this vibration yet? I am running the same drivetrain (427W) and aluminum flywheel and am experiencing similar issues. Just wanted to to see if you made any headway, plus it would probably save me time and anguish if you could narrow down the possibilities.

Thanks,

Chris

[sllib]

Me, too.
Bill Stradtner

[emanon]

The first clue was that the problem started right after you cleaned the engine........ I do believe Clois is right. Make sure you dry out the dist.and cap.
Always try the easy stuff first.

E

[DC COBRA]

TONY

I had a very similar problem on one of my dirt modifieds with a MSD system. Washed the motor, she was a little warm nowhere near hot, evidentally enough to put a hairline crack in the cap. Once they start arcing they never clear up, slight vibration when dry revving it and coukd feel it running the car, slight vibration noticed. When it arced, it usually messes fire on two cylinders there fore the vibration. I think I would replace the cap and rotor and spray some good brake cleaner inside the dstributor that will get rid of any moisture and ****aminants if any.

GOOD LUCK
DON

[Tony Radford]

Upon further diagnosis, it was determined that the problem was inside the engine. After pulling the motor and pulling the pan, it was determined that my main bearings were shot. No apparent damage to the rotating assembly, just the bearings. They're pulling it apart, align-boring the mains and putting her together with new bearings. I hope this doesn't happen every 12K miles!