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944 Engine Vibration, Balance Shaft

  • 1988
  • 944 Turbo
82 000

I bought this car with a persistent engine vibration. The engine has plenty of power, good boost, but there is a buzzy vibration. Previous owner (PO) wasn't forthcoming about the reason he stopped driving it "many years ago". But it seems to have started after the PO had the timing belts and water pump changed 10 years ago. As he hadn't put 1,000 miles on it since the timing belt job was done. I've got the front of the engine apart so I can examine the belts to look for any "obvious" cause of the vibration. After reading the previous replys to questions I'm hoping that the issue is a simple balance shaft sprocket improperly installed.

My question is this: One of the things that I think I've gleaned from the response to other balance shaft questions/responses is that the balance shafts should spin freely and if you spin them their inherent "balance" should naturally land the shaft with the divot in the shaft for the woodruff key pointing upwards. Then as shown in the diagram on page 13-5 of the Turbo Engine manual the upper sprocket should slide on the shaft with the keyway near the 0, and the lower sprocket should slide on the shaft with the unmarked keyway (but again with the woodruff key pointing upwards). Is this correct?

My next question: What if one of the balance shafts doesn't spin freely? The upper balance shaft on my engine spins very freely and naturally lands with the woodruff key divot pointing straight upwards. The lower balance shaft does not spin freely. It will turn but it takes some effort. It is so tight that it doesn't have a natural landing position when given a "spin". It doesn't seem like it's "locked" or that there is any roughness -- from a compromised bearing -- during rotation, but it does not spin as light and freely as the upper shaft. Should the balance shaft spin so freely that it can be turned with two fingers? For example, I can spin the upper balance shaft with two fingers with the sprocket removed. I can't budge the lower shaft with my hand with the sprocket removed. If I put the sprocket on the lower shaft I can make it rotate with some effort.

Any help you can offer would be greatly appreciated.

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