Slight vibration in engine...RPM dependent.

[JRod]

I finally have 3K miles after my rebuild on the 4G63T. Ever since I got it back, there has been a rotational vibration from ~2850-3300 rpm. It does it in every gear, on boost or off, clutch in or out, at any speed. I had thought that it was just a little tight from the rebuild, but after 3000 miles, I still feel it. The people who rebuilt it said it was my exhaust resonating but the exhaust was on there for a long time before the rebuild.

I have narrowed it down to (1) balance shaft belts not in time, (2) bad harmonic balancer, (3) not sure what the hell. Could it also be timing???
I only drive 750-1000 miles a year in this car, but I really don't want to push it if there is something terminal.

Any ideas ffrom the DSM elders' will be appreciated.

 

[Agent Ezzard]

I'm leaning toward the balance shaft belt that is not correctly lined up. I know I vabrate a little in those areas but then again I have no balance shafts and Prothane motor mounts. Do you have stock motor mounts? What kind of shape are they in. If the harmonic dampener is bad your AC and alternator belt would be torn up or thrown off the pulley. Look for any unusual motion in the pulley when the car is at idle. I am still leaning toward the balance shaft. Which one, I dunno. Pull the cover and check when you get some time.

 

[JRod]

I'm pretty sure it isn't the motor mounts, they are brand new, factory pieces. I have no problem with belts being thrown off, and there isn't any excessive wobble from any of the pulleys. I know it will be a pain in the arse to check the B. belts, but what should I look for to see it they are timed right??? Thanks for the help.

 

[Agent Ezzard]

Yes. Check to see if the oil pump and balance shaft pulley timing marks are dead on and that your timing belt isn't too tight.