Zu_langsam

I bought an 86 951 last week. The car is in nearly new condition in and out but it has some mechanical issues that I am trying to sort out. The worst of these is an engine vibration that I am trying to diagnose. When I first bought the car and drove it 700 miles home the vibration (a very fast vibration) was really bad. I checked the balance shaft timing and they looked to be 1 tooth off. Vibration got better, but it was still unaccpetable. It is and was present throughout the rev range but was especialy bad around 3000. After re timing the balance shafts the vibration seemed to move up to 4000 rpm and be a little better. Today i replaced the motor mounts. The car felt better at idle and below 2k but again a really bad vibration aroun 4k and up was still there. I took the balance shaft belt off and its the best that it has been yet. very smooth below 3k, and almost acceptable above that. I still veel a bit around 4k though. Does anyone know if this is around the rpm that the engine is naturaly out of balance? Who runs sucsessfully without the balance shafts? Acording to the factory manual and the visable marks on the pullies, including the O mark that is visable though the front cover plate on the pullies the shafts were timed right. I am a little concerned. Thanks

Rob

Check and see if the balance shaft pulleys have been installed on the balance shafts correctly. The pulleys are the same for the upper and lower balance shaft and have 2 keyways each. They should be installed as shown in the following picture from the factory manual.

TonyG

Great pic Rob.

Zu_langsam

Rob. Thanks for the replies. Well I deffinatly can not see the U through the lower pulley. Only the O through the hole on each. I will pull the lower pulley off and take a look. I think I will post a pic of what I can see when I get the car back up on the lift. You think i will be ok for a little while without the belt?

Ahmet

I don't want to sound too conclusive, but I think you'll be alright w/out a balance shaft belt at all for a little while, as there are a few people running the cars w/out them. I'm almost willing to bet money that the lower balance shaft on your car is installed incorrectly, we'll get around to that next time you have shop space.
Ahmet

Ahmet

The pulleys are indeed installed like in the picture, however w/the balance shaft about 160 degrees off for the bottom one. This means you see the timing mark on the back of the pulley, and the "o" in the "right" orientation, but the shaft (along w/it's woodrof key) is off. Basically, last time we were working on the car, we timed the upper one correctly, but since the lower one has the orientation of the pulley (along w/it's nice timing mark) in regards to the actual balance shaft off, the vibration was still there.

See my reply on the NA board.
Ahmet