Ben

I finished up my TB job last weekend. I didnt change the WP because the TB and WP were both done a couple of years ago. I was mainly changing it because of poor tracking, ie to the front of the sprockets.
I changed the upper idler, lower idler bearing, the tensioner pulley, the tensioner arm bushes, the shoulder bolt, crank sprocket washers, and rebuilt the tensioner. Maybe I should mention that the tensioner was seized solid and had no oil in it!
First off, there was less play in the old tensioner pulley than the new one. But the old one was really noisy. There was slight play in the new upper idler, but there was in the old one too. There was still slight play in the tensioner arm pivot.
The WP pulley also had slight play, but no more than any of the other new components. It spins freely and is quiet.

When I first put it back together, I tensioned it all up to the middle of the window in the Kempf tool, and it was tracking more to the front, but I felt comfortable with the position.
After about 50 miles, and multiple short journeys, the belt tension light came on. This was immediatly after a hard acceleration.
I went straight home and took off the top cover to check the tension, it was then when I noticed the belt close to the front edge, and the printing was wearing off already! Tension was good though.
If all this 'slight play' in the new components is normal, then from what I have read, it looks like i'm going to have to change the crank sprocket. Does anybody agree?

UKKid35

i can't see how the crank sprocket is going to be the cause. Since you're a member how about posting a couple of pics to illustrate the tracking issue.

Did you replace the extortionate tensioner arm bushes?

ROG100

Tracking to the front of the cam gears is usually caused by a bent pivot pin and worn tensioner arm bushings.
You mention you changed the bushings but I see no mention of the pin.
You may want to go back in and replace the pivot pin or even consider an upgrade to the later style pivot arm bracket from the pivot bolt to the WP.
Do a search under my name ROG100 for details.

I used to live in Brent Knoll - fond memorys.

Ben

I read through the archives and that seems that the crank sprocket is a likely culprit.

I did replace the tensioner arm bushes, a bargain at £12 each for a little sleeve of plastic! And the pivot bolt too.

I'm off out today to pull the engine out of my 500SEL, but i'f i'm feeling motivated after doing that, i'll pull the covers off the 928 again and take some pics.

So Roger, are you from England originally, or just lived here for a while?

Cheers,
Ben

the flyin' scotsman

Ben.......you'll probably get much opinion on this but you could set the belt tension at the 'tight' end of the window on the K belt tool. The factory recommends a 1500 mile check after belt replacement as its normal for it to stretch mostly when new. After that it should be fine with re-checks annually....at least thats what I do.

As Paul suggests post some pics and let us see how close to the front edge its running. Are you referring to the cam sprockets?

Ben

To be honest, all of the sprockets looked good to my untrained eye. Cam belt systems are new to me, all the other cars i've ever messed about with have chains!

ROG100

Ben,
I am with Malcolm on setting the belt on the tight side of the window on the Kemph tool.
Once everything is settled you can recheck at 1500 to 2000 miles.

I have found that setting in the middle of the window of the kemph tool will give you the odd TB light.

BTW I sell the complete set of TB parts that you may need and the Tensioner Arm bearing is $17.
More like 8 UK Pounds. Every little helps.

PS: I am a transplanted Brit

Mike Frye

Ben,

I did my TB/WP job in December (set in the middle of the Kempf tool) in January I got a TB light and checked it, it was fine, but I moved it up toward the top of the range. I think if you go for 2/3 to 3/4 of the way to the 'high' end of the range it will be fine and not trigger the light.

Also, without pics it's hard to say, but mine runs about 1/8 inch from the front of the cam sprockets consistently. Most opinions I've read say it's fine if it's not riding along the front lip or causing uneven wear. Also that the tensioner arm is the only thing that could affect this as all other parts are in the same plane and have no pivot whatsoever (assuming water pump pulley is good).

UKKid35

Price per pair from Porsche UK - approx £60 - $110

H2

Although it's not printed in the directions, that I know of, the wonderful Kempf tool (I really mean it) and, on my '85, at the center of the window I'd get the Tbelt warning light. This prompted me to take my car to who's generally known as the best 928 mechanic in the NW. He calibrated my Kempf tool against his 9201 Porsche Tool and said that the 5.2 setting was really slightly "out of the window" on the high side. Center setting was about 3.0. So, I bought my own 9201 tool and this has been verified....and I tried this on two different Kempf tools, corresponded with Jay, etc.

So, I think it's now general consensus that, with the Kempf tool on 32V engines, you calibrate to the high side of the window to keep Tbelt light happy.

Unlike the 9201, the Kempf tool is SUPER FAST AND EASY TO USE, and even though I always double check my Kempf settings with the 9201 (PITA) it's not really necessary if I set it to the high side of the window. The 9201 however, is great and easy to use on the Alt ribbed belt..which, btw, is tighter by "feel" than you think it ought to but...but it's not critical like the Tbelt.
On your belt, anything that touches the belt is suspect.

Harvey

mark kibort

on some waterpumps, and yours may be one of them, there is a little thin washer that keeps the roller assembly more solid.(instead of a little movement radially) i didnt add the washer, but on some PETs it there. so, subsequentially, the belt will run toward the front of the pulley. as long as it is not over the pulley you should be ok.

mk

Bill Ball

Play in the pulleys and bushings...

There really shouldn't be any. A new tensioner pulley and the WP pulley should be firm and even have some resistance to turning compared to an old one. Even my original WP pulley was tight when I removed it at 95K miles. It rotated more freely than the new one, but there was no play. Maybe your fingers are more sensitive to it than mine. Of course, a few thousandths is not going to account for mistracking.

borland

I think most mechanics misuse the Kemph tool. This results in belt warning lights and possible overtightening of the belt. The tool is accurate, but requires belt only be measured while the engine is at cylinder #1 TDC.

Also, after any adjustment of the tensioner adjustment screw, the engine must be hand cranked two full revolutions until the engine is again at cylinder #1 TDC, prior to rechecking the belt tension with the tool.

Ben

Roger, When I changed the tensioner arm bushes, I think I payed something like $20 each from 928 Intl. I'll know for in a few years time when I need to do it again though!

The old belt was flush with the end of the pulley, which is the reason why I changed all the gubbins. You could see on the crank sprocket washer where the belt had been rubbing up against it.
From what I remember last weekend, after I pulled the top cover to recheck the tension when the light came on, the new belt had moved to approx 1-1.5mm from the front of the pulley.

I didn't get round to taking any pics today, I only just finished pulling my engine. I'll do it tomorrow and update then.

Mark, I'll check on the washer. I didnt put it back together with one, maybe it'll help.

Bill, Regarding the play in the pullies.... You couldn't see it, but you could feel it ever so slightly. Maybe like you say, my fingers are a bit more sensitive sensitive with feeling it.

Ben

I didn't have chance to pull all the covers back off, but I whipped the top one back off to take a couple shots.





I adjusted the tension up a bit, its about 3/4 the way into the window now.