I recently went thru a complete top end tear down to find the source of an LDK internal coolant leak. I know these blocks aren't too famous for going "porous" so I changed head gasket, and later water pump. It appears the water pump may have been the problem. Still watching. In the mean time.......

When I run the engine it runs smooth, but up at almost exactly 3300 rpm in get an engine vibration. Any gear, and goes away when I put the clutch in. I have torqued and retorqued engine and trans mounts many times, put my old harmonic damper on and got my ATI rebuilt. Same results with both. I am running neutral balance shafts, so shaft timing is not an issue, and I didnt have the vibes before. I'm getting ready to pull the front cover again to double check chain guides. Any ideas?

 

Sure it's not coming from the trans? If it doesn't vibrate when the clutch is depressed I would be looking at the driveline/trans.

 

What I meant is if Im driving at 70ish/3300 rpm it starts vibrating. I push the clutch in it stops. So that kind of rules out the trans, Seems the same rpm it vibrates in each gear.

 

When you push the clutch in are you also letting off the gas? What happens when you try to hold the engine at 3300 rpm in neutral? Did you just install the neutral balance shafts when doing the water pump or was that done prior to this round of repairs?

 

Yeah, does buzz at 3300 sitting still clutch in. I had the neutral shafts in for 30k miles. This is a new issue as I didnt have the vibes before. Seems as though its something I did as it just started after I got everything together from doing the head gasket. It feels like what a bad damper would do, although I had the ATI on, then the factory damper, then the rebuilt ATI and its all the same. These things make me nuts

 

You don't think it could be something weird like your exhaust rubbing against the body of the car or something like that? How intense are the vibrations?

This question doesn't have anything to do with your diagnosis but out of curiosity why did you need to have your ATI rebuilt?

 

Exhaust is a possibility, but the very specific RPM it comes in at makes me suspect it isn't. But is possible. The ATI was pretty stubborn getting off, even with a good puller. It was in the back of my mind I may have bent something, so it was cheap insurance to get it rebuilt.

 

Exhaust is a good idea to check. You know at certain rpms it does harmonically vibrate more than others.