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

iloveporsches

You can run without the balance shafts without much problem. I know David Floyd (Sorry if I screwed up your name) has a motor from Anderson that has the balance shafts deleted. I drove around for two weeks with a broken balanceshaft belt (didn't know!).

But what it sounds like is you ahve it 180* out of time. Usually if that's the case you'll get bad vibration at like 3800 RPM, which is what is happening to you. Make sure you have them the right way.

Zu_langsam

I have not had the pullies off yet. I do not have the spanner tool to put them back on so I have not taken them off yet. By looking at them and the factory manual I do not see how they could be off 180 (actualy i think its like 160) off and still have the O mark showing through the opening in the front of the pully plate thing.

Rob

check out my reply in the turbo board posting. When installed correctly, you should not see the "O" through the hole in the washer on the lower pulley.

'88-924S

i just suffered through this on my 88 924S. IF the pullies(sp) are installed correctly, the "O" on the upper pulley should show through a round hole, and on the lower, it should show through a rectangular hole. The marks are on the back plate of the pulley and should line up with marks on the back timing belt cover(upper about 1 o'clock, and the lower at 7 o'clock.) It can be difficult to make sure once you put the belt on and tighten the belt to keep the marks lined up. Once I got the marks right-bam-smooth once again. Good luck.

Ahmet

Yes, the above post is correct. The previous mechanic installed your lower balance shaft pulley like you said about 160 degrees off, which is most def. good news for you. I think I'm going to be out of town tomorrow, but I can take care of it for you on wednesday. If you set it up on the lift etc. it should take about 15 mins (but you know how that goes), I won't need the spanner either. I will have an extra belt w/me.

I need to bleed the brakes (did the pads today @3am), and replace the coolant on mine, you think wednesday we can knock both of them out? Let me know when you get a chanse.
Ahmet

Zu_langsam

Ahmet, I think that we can manage a "late night" wed. and knock this stuff out on both of our cars. Thanks for all the help guys!

major

Don't know if this applies to the 951 or not, but on a 944S you can actually flip the balance shaft pulley (the gear itself) 180 degrees and when all is reinstalled and timed it looks perfect. However, the balance shaft will be out of time. Been there and done that. A shop had to straighten me out on that one. Could your previous owner have installed this balance shaft pulley wrong. Hope this hasn't confused you and you are able to get your problem sorted out.

Zu_langsam

Major, Thanks for the reply. I think that is the problem. I am going to have the car on the lift tomorow and see if I can straighten things out. I am really interested in hearing from some people who run their cars without balance shafts, I want to know how it feels in their cars w/out them to compare.

kennycoulter

so if the belt brakes, how bad is the vibration? what exactly would it feel like? i feel a vibration growing from 3000 and up when i keep my hand on the shifter(this is in all gears) not a very bad shake but noticable. any clue if this is the same problem?

Peckster

If you think you might have a broken belt you should not start your car. The pieces can mess up your timing belt.

kennycoulter

really? do my symptoms sound like a belt, or a driveline vibration though? i dont have another car to drive right now.

Peckster

If a belt broke it would have started suddenly. Mine doesn't vibrate now, I can't recall what it was like. I do know that vibration at idle is probably motor mounts, vibration higher is balance shaft out of phase.

Does the vibration change with speed? Is it there when the car is not moving? Clutch in and out?

Dave951M

Could very well be but the vibration with no balance shaft belt isn't that bad. You could also have a couple of extremely bad bearings in your torque tube. The factory put in 4 bearings spaced to dampen crank harmonic vibration being transmitted down the driveshaft. If you're feeling the vibration in the shifter, I'd about bet that's what it is.

Matt H

For the record you can pull of at least the top covers to check in a matter of a few minutes. After the first time it shouldnt take more than 15-20 mins to pull the top covers and have a peek (should be obvious if it is missing). I know I have no plans to reinstall the covers on mine at all, the bottom are still a PITA.
__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote