JG928S4

TB Timing belt warning light

I have recently had the Timing Belt warning light come on during hard acceleration. I have looked at belt through the inspection covers, looks good to me, the warning light goes out upon restart and does not come on unless hard acceleration, but not consistently. The belt has about 25,000 miles on it. 88 928S4 AT.

I have done what I thought is a thorough search for what to check etc., adjustment? Time for more dis-assembly?

Suggestions

pcar928fan

Time to reten the belt or replace if it has been more than say 5 years.

My S4 did this recently too. After it was replaced it came on in 5 miles, then it got to where it would come on at anything just above idle. Got it retened and everything is good again...not to mention a new belt, so that is a nice feeling!

WallyP

If the belt breaks or sheds some teeth, you just wiped out the engine...

I would suggest that you carefully inspect the belt and all rollers, and adjust the belt using either of the common tension gauges as a absolute minimum.

David L. Lutz

Get yourself an after market guage, take off the right cam cover, inspect and check as much as you can, then check the tension. (there are several good write-ups on this)

If all looks good and the tension was just a little loose you should be OK (for now), and the above process is fairly easy.

How long ago was the belt changed? At 25000mi. you my be getting close to just going ahead and replacing the belt.

+1 to Wally's caution, and I wouldn't drive it until I at least took a look and checked the tension.

Good Luck

davek9

+ 1 on checking the belt and tensoner rollers, and many GREAT write-ups...but PLEASe check for oil in the tensioner.
This is by far the most neglected item, if the internal parts can not (move) i.e. retract when hot, you will distroy the all the gears from runing too tight!
A few of the MI guys did an 84' Euro over the weekend, the tensioner was dry and froze up. now the owner is buying all new gears.

Here is a pic of his oil pump gear, he thought this belt was serviced over a year ago, but they never checked out the tensioner.
Take your time and do it right...

Lizard928

HOLY CRAP!!!!!!!!!!!!! I have never seen a gear worn that bad.

Alan

Me either! I have a worn cam gear here in my office off my GTS. It doesnt look even 1/10th that bad (maybe 1/50th?) ... shocking... that belt would be jumping soon - just no tooth left to engage. Maybe the excess tension was all that was keeping it seated in there...? nasty.

Alan

ew928

That worn oil pulley gear looks like those drive pulleys on tanks.
Yikes!


At least the belt will always ride centered with a gear like that.

cold_beer839

Add some gear oil to the tensioner and retension the belt if it looks good and only has 25k on it (but it isn't over 5 years old).

If you put this off you will be looking at lot of broken valves.

Bill Ball

The oil pump gear is way off the charts! WOW!

Mrmerlin

This was a very fortunate catch.
What kind of belt are you running?? square or round??
This looks like an old style oil pump gear made of aluminum, the new one will be steel .
If your still running with square tooth gears its time to upgrade to the round tooth gears to include the crank drive gear the oil pump and the cam pulleys plus a HTD ( hi torque drive belt) put the belt on so you can read the label on the belt as you face the engine.
I like to use STP oil in the tensioner it takes a while to fill with a small visene bottle. Also consider replacing the oil pump radial seal and the oil pump O ring. use STP to prime the pump and make sure to have the small dots on the gears facing the engine the bevel on the outer ring gear faces the pump..... other way around and the pump will seize. Goodluck!

RKD in OKC

My toothed belt light came on. It had only been 2000 miles since new belt, pulleys and water pump. The tension was 4.8. The screw holding the tension warning sensor had come loose. Whew.

Jadz928

Speaking of fortunate catch... that same car with aforementioned oil pump gear (ouch) visited me in Richmond right before the Porsche Parade. When he pulled in, we popped the hood (isn't that what all 928 guys do before the obligatory guest greeting?).
I heard an odd sound and isolated it to the right cam gear. So we pulled the cover to check tension. The belt could slide across the sprocket! Way loose....
Gave it a retension to spec, with the bolt at max travel.
I told him he got lucky. Then we proceeded to tear it up to the Porsche Parade, AND he made it back to MI to boot.
He knew first thing on his list when returned home was TB/WP. ...and apparently and OP gear. The TB systems are more robust than we give them credit for.

davek9

Hi Jim, Stan told us the story and how you came to his rescue, don't want to thread steal here , just wanted to point out that really bad things happen to the gears when a properly tensioned belt can't de-tension when the engine get hot. Thanks for all the tips, and yes this was/is a HTD system, we replaces all oil seals, Cam, Main, OP and removed it and did the O ring too.
Here are some parting shots of the happy owner and that belt alignment gear in action..

Dave K9

PS: Oh .. and WOW that is the worse gear we ever seen is exactly what Dennis and I said too, we were amazed that it was holding up!!!

Big Dave

Stan ...of course it was Stan