Jaycobsladder

I have a 66 coupe base model (300 hp/327 automatic ) the engine was rebuilt some time ago but sat most of the time. I have had it for a couple of years and drive it religiously every 2 weeks. I get a vibration at about 1500 rpm, 2500 rpm 3500 rpm. (Static,in the garage ) l am thinking it's the harminic balancer. Any help would be greatly appreciated. MARK

MikeM

My experience with engine vibrations tells me if the cause of the vibration is internal to the engine, it will come in hardest at one particular rpm. It's been a long time since I diagnosed an internal vibration so take this for what I'm charging for it.

I'd make sure the exhaust isn't grounding to the frame somewhere.

Remove the fan belt and see if the vibration goes away.

Put the car in gear, with the clutch pedal in and rev the engine to the affected rpms. Did the vibration go away?

Check the easy stuff first.

I've never had a harmonic balancer fail so I can't comment on that.

A-Snake

It's an automatic

AZDoug

A harmonic damper doesn't really "balance" an engine, unless it is 400 or other motor that is externally balanced.

The damper is tuned to a specific frequency that your crank shaft will set up self destructive vibrations at that you probably can't even feel, and IIRC, this is something that only happens at one RPM range in the motor.

I would look for something else first as Mike M suggested.

Doug

Bluestripe67

Since its sitting still and and running, you say, "I get a vibration at..." do you hear and feel the vibration? Have you checked the alternator mount. If it has P/S, check thr pump mount. If you put the car in gear, does that change things? Dennis

pop23235

AZ, that's not exactly true. I'm too old to remember the correct number, but the harmonics set up at multiple rpms. I think the first is around 1700 rpm, the second at about 3400 rpm, and a third at about 5100 rpm, and a fourth about 6800 rpm if you haven't floated a valve by then. The basic small 327 harmonic balancer is good for the first two, figuring not many even 300 hp 327's will spend much time at or above 5100 rpm. The much heavier 340/350/365/375 balancer is actually not helpful to the output of the engine, but will dampen the first 4 harmonics. Now, don't quote the exact RPM, but you see the pattern.

AZDoug

http://www.bhjdynamics.com/index.php...ek8av8l1d37od7

MikeM

I broke a crank years ago due to having the wrong harmonic balancer on my SHP 327. I never felt the first vibration. Same thing with four of my buddies running the same engine, same rear gear, and same driving habits.