fletch.

All 944T's have a distinct whine, it’s a topic that comes up every now and then with me and some other turbo owners. Our general consensus is it’s the balance shaft belt. Some cars are much loader than others, I am thinking it’s the tension on the belt that changes that. If this is the case my belt is either tighter or looser than it should be. My car seems to be the loudest of the 3 we compared.

This brings me to the belt tensioning tool, which I just used to reinstall my belts after the lifter job. It seems like depending on the location (a couple teeth up or down), I get a slightly different reading each time I check the belts. Anyone else have this problem?

Cobbs

Dont have a 951 but definitly have that whine. I also believe that it is coming from one of those two belts. I am a poor guy and used the "kricket" when I did my belts so I'm sure I'm not achieving the precision of tension that is required. The shop manuals refer alot to "pretension" on the belts. I am not positive what that means but I think it has somthing to do with how much tension is on certain parts of the belts at different points in their circuit. That is only a guess though... I also experienced varying tension readings on different points in the belt and so I tried to take the readings closest to the middle span of the belt. I realize after writting this whole thing that I never really helped you at all. Sorry about that. Hopefully somebody can give us some good info.

aka 951

A lot of the time the whine is coming from an improperly adjusted balance shaft belt. It seems like 9 out of 10 of these cars have it. I played with the eccentrics on the balance belt rollers after I did the belts about a year ago and my 924S has not whined since - try that.

PS - i don't really think the tension on the balance shaft belt matters all that much, just as long as it feels "right". Oh and Fletch, you're not the first one to figure out that the factory belt tool is just an "approximation"...lol

Erick

keith

Actually, the factory tool is VERY precise, hence the problem... The factory should have put a reference mark on the back belt cover, to provide a consistent reference point for using the tool. Logic should tell you that the most belt deflection would be detected at the middle of the long span, so put it there. Another issue that a LOT of people miss, is that if you twist the tool to an angle that allows you to read it while it is on the belts, you are applying more force to the tool and throwing your measurement off... I take great pains to slide the tool straight off the belts and then use the telltale to make my reading, or use a mechanics mirror...

About the noise... apparently there were and are different belt compositions out there. In addition, another lister had compelling evidence that the actual SHAPE of the teeth on the belt cause the noise. This would make sense with experience, as slightly different tooth profiles from belt to belt would account for changes in whine/volume, etc...

It is my opinion that "fiddling around" with the eccentrics to stop the whine is probably not the smartest thing to do...

MadMax

Here's my two cents about the whine. I asked one the Mechanics(big fan of the 944 series by the way)at Brumos Porsche (unquestionably one of, if not the most reputable porsche dealership and shop in the country) and he told me specifically that the whine is normal IF the belts are tensioned correctly. He pointed out the the fact that the car did not whine prior to the belts replacement and re-tension.

I asked the mechanics again at Valley Motors in Baltimore, MD (where I live now) because I had them to the 2000 mile adjustment and they said the samething. Although, I was asking them more to get a feel for their knowledge rather than to check what the guys at Brumos told me. Not too impressed with Valley Motors. I digress. Anyway, the whine is normal, if your belts are adjusted properly and I would be cautious about attempting to adjust the whine out of the balance shaft belt. Proper function of the balance shaft belt is what prevents vibrating the motor out of the car. It will shorten the life of your motor mounts and can potentially damage other drive train components...per Brumos Porsche.

aka 951

LOL - Porsche would not have sold so many of these cars if they whined from the get-go.

Erick

[ 06-15-2001: Message edited by: aka 951 ]

fletch.

I agree with the reference mark idea on where to use the belt tool. I probably will go back in to check the belts again in a week, but my past experience tells me they will be no where close to what I measured when I installed them.

It seems very unrealistic that one of these belts would jump teeth. I have seem some so loose I could almost pull the belts off by hand. Anyone seen a belt jump?

John Chasse

Can someone describe this whine? Is it at idle? Only under boost? All the time? (I guess if it's the balcne shaft belt it would be all the time.)

How does the sound differ from tourbo spool-up and intake noise?

Eric

I just had my belts re-tensioned on Tuesday, and I have the whine. It occurs mostly at idle--as far as describing the sound---I guess you could call it a Hum. I only notice it if the radio is off or I am out of the car for some reason. During spool-up, the whoosh of the turbo drowns out the belt hum(at least on mine). I can (and have been)live with it. (nice syntax)

Eric

Tabor

Propper tension is meant to reduce stress on the rubber itself. Not to make sure they don't hop off. If they are too tight, or too loose, the rubber compound is getting too hot!

Or, this is what I have been told. YMMV.

OZ951

Balance shafts came up in a conversation with some other 944 guys I know and a couple of them had heard that the engine can actually be run without the balance shaft belt installed. As the story went it made little difference to how the engine felt in terms of vibration. (whine/sound did not come up in the conversation).

Personally I certainly would not do without the balance shafts. I don't expect Porsche would have complicated their engine design (and subsequent impact on reliability) just for the hell of it.

Wayne.

Tabor

Wayne: The story does that the 944 engine ran smoother without balance shaft belts than the Mitsubishi engine with balance shaft belts that they were using as a guideline.

FYI: Did you know that Mitsubish Patented balance shafts? Auto manufacturers had to pay royalties to use them. I assume the pattent has expired by now.

keith

more about the balance shaft belts: a lot of racers remove the belts/shafts completely, from what i understand. The Mitsubishi guys (starion/conquest) have a kit available to COMPLETELY remove the balance shafts, which they claim increases OIL PRESSURE. Perhaps a benefit for Porsches (regarding #2 rod bearing starvation issues)?

On the vibration issue, I experience vibration at idle with new mounts and properly timed belt. I assume this is due to the composition of the updated turbo mounts transferring a lot of motor movement to the chassis, as opposed to the old fluid filled mounts. The dampening effect of the balance shafts was probably more effective with the softer, original mounts...

On the tool issue, FLETCH, it is possible - my belts have been spot on, when rechecked after a year of use. I will be doing the two-year replacement this August, and will check again, but I'd be suprised if they are off at that time... It takes some repitition to get the hang of it, but repeatable results are achievable. Also, the tool goes out of adjustment, and must be calibrated regularly as well.

keith

BTW, the whine sounds like an electric motor.
(at least to me...)

fletch.

Good description of the sound Keith. I think I need practice with the tool, I think I'll go back in this weekend and play with my readings.

Is there anyone that has first hand knowledge of the affects no balace shafts have on these cars? I have heard several conflicting accounts.

1) 944's will be fine above 3500rpm, below the vibration is about double.
2) 944's will rip the motor mounts apart from the torque load without balance shafts. If you go to solid mounts it's fine. who the heck wants to do that? you would have to check every bolt on the car every few days