Engine vibration

[mikeyz52]

Ok yesterday I go out to go to work and start my car and it has a horrible vibration. It seems to vary with engine rpm, and happens weather the car is moving or not. Motor mounts have been updated to turbo ones. I'm thinking the balance shafts must have jumped timing somehow? The car seems to be running fine, just has excessive vibration. Any ideas? The car is a 84 944 NA.

[honerboys]

i'd would stop running it until i'd pulled the covers and checked out the belts - it could be the balance belt has broken and is just hanging in there or the tensioner has loosened - if it's either of these it's a disaster that's just waiting to happen

[mikeyz52]

Just went out and let it run in the driveway for a few minutes. No vibration at idle, and then a vibration that increases with rpm. Doesn't seem as bad as it did at 3am yesterday, but definatly noticible. Time to pull the belt covers I guess..

[mueller944s2]

I had posted this about an hour ago so I just cut and paste:

Go look at your balance shafts again. I had everything lined up fine but something came loose and it started vibrating because it was off a couple teeth. We got it lined up again, started it, and somehow that lower sprocket ended up 180 degrees the other way. Lined everything up and tightened the belt again, started it, and once again 180 degrees the other way. We did that about 4 times until everything stayed put. No idea what caused that mess but everything is fine now! (all belts and rollers were brand new btw)

[mikeyz52]

Found the balance shaft drive belt loose. Probably has just jumped a tooth. Weird that it was fine when I parked it, and must have jumped as soon as I started it the next morning.

[flash968]

starting the car puts the most load on belts. you are going from zero to startup instantly. that's why a very large percentage of belt failures happen at startup.