Porsche Enthusiasts Club Forum

At around 1600 rpm and 3200 rpm there is a vibration coming through the gear stick. Clutch in, clutch out, stationary, moving, any gear - it's always there at 1600 and 3200 rpm.

The balance shafts were checked out and were set up correctly. It was then decided it was the engine mounts, so they were replaced, but it didn't cure the problem.

This has happened for a long time now, and I've learnt to live with it - but it shouldn't be there and it's very frustrating because I have to cruise at 3000 or 3400 rpm, but the latter is a bit too fast for our motorways - so of course I don't do it

Any ideas anybody?

These are classic balance shaft speeds. Especially 3200rpm. Who checked them? I ask this as some of the manuals were wrong with the belt runs & the specialists know this. If it's clutch in & out then it must be engine related. And most of the rotating parts would give a vibration at all RPM.

This happenned to my car when the balance belt was one tooth out. Caused all sorts of grief, eg fractured rear silencer heat shield, oil filter working loose with resulting oil pump-out, and maybe more problems as yet undiscovered.( I'm worried that the oil pickup pipe could have possibly become cracked as I've heard that this can happen.).

I think the belt can only follow 1 path.

I believe the rotation direction of the tensioner is the issue in the manuals -which I am told can affect belt life but not the balance.

Those with more knowledge correct me if I am wrong.

Anyway the problem does sound like the belt.

Rich

How do you check if the belt is 'one tooth out'? If the balance shafts are in the correct position then how is the belt a tooth out?

The balance shafts need to be aligned with each other, the crank & the cam so 4 alignment points. The attached is a copy from the Porsche manual cropped just for the balance alignment. This is with everything else at TDC (OT)
Note this isn't the way I'd have guessed they went so quite likely someone not familar with the job would be wrong as well.
Also the belt runs quite slack & if the car is pushed started, stalled whilst running could jump a tooth.

My balancer belt jumped a tooth when almost on the rev limiter in third; my fault,car had stood unused for 3 years, so should have changed all the belts as part of the recommisssioning process.(they have been done now of course).

Updated 07 July.

Today I had the cambelt and balance shaft and all tensioners and rollers replaced, and the car serviced. Stewart took extra care setting the balance shafts, yet the vibration is still there, exactly the same at 1600 and 3200 revs.

Stewart has asked if anybody has heard of the shafts breaking and causing the problem.

Any ideas?

I have heard about the shaft breaking but not often usually when the bearing seizes the shaft stops turning and from what I understand the bottom one is the one which goes most often. With the car on a lift you can hear the bottom shaft turning and if you put a long screwdriver to the shaft housing you can hear out a noisy bearing. Alternatively you could disconnect the balance belt and try turning the shaft from the pully wheel by hand to see how stiff it is. I seem to remember someone on this forum posted something about a balance shaft seizing completely towards the end of last year.

I'd try it without the balance shaft belts on at all. If it cures it then you know where to look. Will only vibrate a little at low revs.
(Race boys run without them so don't worry.)

Stewarts already asked me to take it back to him so he can run it without the belt on.

I'm going to have a look at the set up myself on Sunday. I'll just be checking the settings and orientation is correct.

If I did run it without the balance belt on and it didn't vibrate then I wouldn't know where to look.... so what do you mean? Or if there's no vibration should / could I just leave the belt off?

Hi,

I'm no expert but I think what they mean is that if you take the balancer belt off and run the car and the vibrations have disappeared, then you can assume that the cause of the vibrations must be the balancer shafts.

I think I'm correct in saying that there are 2 balancer shafts so I guess you'd have to remove either one or both balancer shafts to see which one is damaged or whether both are damaged, or if it is something associated with the balancer shafts. I think someone mentioned a bearing earlier in the thread.

Regards,

Ben

Sorry. Clear as mud as usual! I mean if your specific vibration disappears then you know it's balance shaft/belt related. Rules out everything else! It will vibrate without but not a lot & at low revs. Also with the belts off you can check if the shafts spin ok with finger & thumb. But Jims diagram is pretty clear so it could just not be on right! Hope it's an easy fix.

Hi John, i have the same problem with my 944, vibrations at the same RPM as you.

Have you found the problem yet?

Ive realigned by balance pulleys a couple of times, which cures it then comes back again after a short while. ive recently changed my balance belt though so need to try again. ive heard you can get the pulleys 180 degree's out aswell.. because the balance shaft rotates twice to every 1 rotation of the crank.
ive also yet to check the freedom of movement on the shafts with the belt removed.. thats next saurdays job.