Hi All

I got my new belt (Porsche) on last night and was slightly unhappy to bolt it all up.

Its a 1988 S4, I replaced, Belt, Water Pump (German recon), Cam gears, Oil Gear, Rollers, Tensioner Arm bushes, but NOT the crank gear.

The issue is that is tracks central on the passenger side (LHD) cam gear but only 2mm off the forward edge of the drivers side cam gear. It is steady with no walking.

1) Do the folks here think that I should stop being paranoid and just finish off the job?

If not then....is the issue

a) I should have replaced the crank gear?
b) The belt is the wrong way up, from the front the Porsche logo is upside down?
c) I replaced the aluminium oil gear with a steel one...should I lose the spacer behind it?

All these issues have been mentioned in previous threads, but I have noticed on many photos that there are a lot of belts that do not track straight down the middle.

Please advise, as I will otherwise just toss a coin.

Thanks in advance

Colin


BTW I am a Rennlist member...if anyone can help me get my status changed

 

Colin--

I noticed that when I replaced the WP with the rebuilt, the paint on the pivot pin needed to be removed to get the bushings to fit just right. A squirt of brake-clean on a paper towel did the trick for that, then the bushings fit a lot better. A dab of brake caliper grease on the pin and in between the bushings in the arm too, though that's a dr bob addition, not a WSM recommendation. With the pivot bushings on the arm not exactly true, the new belt would track slightly off on the first sprocket following the misaligned tensioner arm, the passenger side cam gear. While the belt is still new, it will track correctly around the rest of the gears fine. As the belt ages and stretches ever so slightly more on one side, it will eventually track off on all the gears. That's the hrad-nosed answer from a machine designer.

Meanwhile, you may find that all your bushings fit perfectly on the pivot pin, your rollers are new, you put new bearings in the guide rollers down by the crank and the pins that hold that guide bearing bracket are not too worn, and in that one place the belt is still a bit forward of where you think it should be. With the new oil pump gear, misalignment from that would show up first at the crank sprocket before the pass side cam gear. If the crank is lined up OK then you can probably discount the oil pump gear change as a possible cause. Go back to where the old belt rode on the pass sprocket before you started. Did it seem to be forward, like the new one is? Another test is to use a long straightedge to verify that the two cam gears line up perfectly with each other. There really are only a few things that can cause the belt to track funny: worn or incorrectly installed tensioner arm bushings, worn rollers, worn gears.


HTH!

 

Hi Bob

Thanks for the fast reply. Seems that I have confused you. The cam gear that is tracking badly is the drivers side one, the one on the right while looking from the front of the car.

The lower guide rollers were not replaced as they turn smooth and have no play.

I will try the straight edge across the cam gears to see if that gives a clue.

The old belt tracked right in the middle of the cam gears but seems that Porsche decided to way over tighten the belt 9 years ago. Looks like they measured the upper belt path rather than the lower path!?!

The only other observation is that the recon water pump did not seem to have a new pulley on it.

Will report more when I know more. I find it a real hassle to get the tensioner arm off and on with the tensioner bolted up :-(

Thanks

Colin

 

Ooops...guess who forgot to put the circlip on the new tension roller?

I took the spacer out from behind the oil pump gear while I was in there.

The belt has not moved back much though. Has anyone any idea of how many rotations it takes a tensioned belt to reposition itself? Or should I have lined up the belt again before I tensioned it?

Cheers

Colin

 

the holbert car has always been at 1 to 2mm toward the front of the pulley. however, on the driver side, its right in the middle. i think it is the tensioner arm bolt and the possibility that i could have used a thin washer to fine tune the position. However, never did it, just replaced the shoulder bolt and the belt doesnt move. just checked my handy work again after this weekends first race, and the belt is the right tension and in the exact same position.

I wouldnt worry about it at all.

Mk

 

The passenger side cam gear sits slightly forward of the driver side gear since the Hall trigger plate is behind it.

 

My bad, Colin. I was reading too fast or thinking too slow... Probably not reading too fast.


The water pump would be the last roller before the driver side gear, and a good place to start the research. Except for the part where there isn't a whole lot that can change with the water pump, except that the roller on the pump is pressed on to a precise position. Before you send the old pump back as a core, measure the spaceing between the pump body and the pulley on both the old an dthe new. You may find that the rebuilt pump has a pulley that's not pressed on as far as the old one. Worth a look and a quick measurement to be sure.

On the rollers: A set that 'feels' fine now when you spin it by hand is a good sign but not a reliable gauge of how the rollers will last under load for another 50k miles. IMHO, new rolers are cheap insurance against some sort of failure during the life of the new belt. New rollers, and bushings on the tensioner arm, take those parst out of the list of possible 'why my belt tracks funny' parts. Too many benefits available. Again, this is just my opinion.

 

wouldnt that make the belt move toward the the cabin?

MK

 

ok

Thanks very much for the replies. The only rollers I did not replace are the ones under the crank pulley. My take on those are that they are an up market bump stop to the belt skipping off the crank gear, and are not normally under load.

I am very glad I went back in, but now I am happy to bolt it back together and check it again at retension time.

Thanks again

Colin