I have a solid lifter LT-1 with 58,000 miles and an engine vibration that I could use some help with. For back ground, this car had a vibration that came on strong as the revs climbed such that I have never seen the 6500 red line and shift by 5000 at the most. I had the engine out for a refresh a year ago and have only put about 600 miles on it since. I did this because it leaked everywhere, was filthy, and was a little low on compression in two cylinders. Because it was low mileage and had no ridge at the top of the bore, I just honed and re-ringed it with no machine work on the block so it is basically stock. I did not pull the crank because the oil pressure was always high (60 or more at cruise, 40 at idle) I had the fly wheel faced and paid extra to have it and the new pressure plate balanced together so I am confident that the source of the vibration is not in the bell housing. I also should add that it does not originate in any of the drive line because it is sensitive to RPM, not vehicle speed, and will shake the steering wheel sitting still. It is no better than before I took the engine out. I have not gone back to check compression on all cylinders since driving it for a year but plan to do that. It pulls strong so I belive it is firing well on all 8. Can a harmonic balancer do this? I am still using the original. Is there anything else I should check? I hate to just throw parts and time at it not knowing what I should be doing to find the problem. All suggestions will be appreciated.

 

I had something similer with my 71. Felt like the engine was going to jump out of the car. It turned out to be loose fan mounting bolts.

 

had similiar issue on my LT with RPM and after long search ended up being exhaust rubbing on the cross member holes. It was the same feeling as the engine was totally unbalanced.

 

Are you saying the vibration existed before you re-ringed the engine?

 

I had a 72 LT-1 that vibrated. Turned out that the u joint on the driveshaft at the rear yoke had been installed with the grease fitting towards the pinion. This caused the grease fitting hump to strike the pinion shaft face. It was speed/RPM sensitive.

 

Yes, I had the vibration before I pulled the enigne for the refresh. It is no better and MAYBE a little worse. Tough to tell for sure. I know it is not u-joints or rearend as the vibration response in the steering wheel is the same when feeding throttle sitting still. The exhaust is stock, properly clamped at the front cross member, and hung on the rubber mounts from there back. The few motor head types that I work with say to try another harmonic balancer. I have no experience with one of these going bad and would like to hear from anyone who does.

Thanks for the input guys!

 

If you're running the original harmonic balancer it sure couldn't hurt to replace it- that's almost 40 years of age and the rubber in it has to be just about shot by now!

However, I've had 2 vibrations over the years that felt like the motor was ready to come apart. One of them was loose fan bolts (my fault) and the other was loose bolts connecting the trans to the engine block ( a helper's fault). I'd definitely check those 2 areas out first since they're simple and easy to correct. Good luck.

 

When I did my engine, I had the machine shop balance the whole rotating assembly, pistons, rods and crank. I think it's good practice to do that.

YV

 

I'd try another harmonic balancer.

 

Ditto on the balancer, although the rotating assembly could also be out of balance since you did not remove the crank and check the balance, and the vibration was there before.

Let's hope the balancer fixes you up

Good Luck

 

good advice, I'd start with a new balancer, then work your way around checking the motor mounts, bell housing assembly, trans, and everything with the drivetrain...

 

http://www.fluidampr.com/CHEVROLET.htm

your assumption about your bearings being okay because the oil pressure is good is bunk. check your bottom end. I would drop the oil pan and get a look. Check the main cap bolts. just my 2 cents.

 

Any updates Paul?

 

The update is that I'm gong to follow the consensus advice and order a new balancer. I'm real sure my fan and bell housing are both tight, but I will do a quick fan check when I go after the balancer by running the car briefly with no fan. Not sure when I will be able to do it. I have to do more business travel next week to the UK then I will be out your way near Erie for a week of vacation. I'm originally from Chautauqua County, NY and my mom still lives there, along with other relatives. I'm flying to PIT so I will be driving right thru Erie when I come up I-79!

 

I had a similar problem, turned out to be the fan clutch.
I replaced it with a GM fan clutch and it solved the problem.
Don't use a cheap Chinese clutch if this is the problem, spend the money for a GM piece.

 

Well good luck with the vibration and make sure to beep when you pass exit 35 on I-90.

 

go even farther and 'pull the main caps and I would also check the rods....but normally not a rod because it would have a definite knock. However a bad main can be felt in the steering wheel and still hold relatively good oil pressure and be RPM sensitive. Should have done that before when it was opened up. Besides it could give you piece of mind....

 

Pull all of your accessory belts off and run it real quick see what happens. If its gone then you have an accessory based issue.

If not I would start with the dampner/balancer.

 

This is what my vibration issue turned out to be. Read my thread.
http://forums.corvetteforum.com/c3-g...last-year.html