Bill Ball

I've been working on a car for a new owner. This is a rather nice 91 S4 with 35K miles that I helped the previous local owner sell. It really didn't appear to need much other than some overdue fluid changes. It had been extensively serviced in 2007, about 8K miles ago, including a timing belt job at a well known independent Porsche shop in Las Vegas. It had an oil change about 1K miles ago, but that was 2008.

Among other things, I did a timing belt check. Tension was right at the low end of the window. It had never had its 1500 mile check, but still, it should have been higher. The belt was "Flennor" brand (?). The cam gears were perfect and had not been replaced according to the records. There was evidence of a tensioner oil leak. I pumped a couple of ounces of oil into the tensioner fill port until it came out the other port and didn't see any leak out. However, after I drove the car, all the oil promptly leaked out onto the floor, apparently from the boot area rather than the gasket. So, I told the owner and recommended it be fixed.

I got into it today and here is what I found when I removed the center cover.



Here's a pic from Dwayne's guide that shows the coil spring under a flange on what is called the "push rod" that is also encased by a plastic insulating sleeve.



So, what? Well, that spring opposes the belt tension. It doesn't provide primary tension to the belt, but as long as the belt tension exceeds the spring tension, the push rod, which spans the gap between the tensioner "piston" (that ends even with the boot) and the arm, maintains contact with the tensioner shaft and keeps a ground circuit closed. If the belt tension is less than the spring tension, the push rod separates from the tensioner piston and the ground breaks, tripping the ominous "Toothed Belt!" warning. Without the spring, the warning never trips, as long is there is any belt tension at all, however low. Here is a link to a very clear visual explanation of this system by Tony Harkin.
http://members.rennlist.com/v1uhoh/timing.htm

One other thing...there is a washer missing as well from the same area. It is supposed to go between the plastic insulating sleeve on the push rod and the spring. It tends to fall off when the tensioner is removed and is not noticed until after the timing belt job is completed whereupon it becomes just one of those leftover nuts, bolts and washers of which we all have a good collection. It's missing in the second photo from Dwayne's guide as well - note it was there when he began the timing belt job. Here it is highlighted in PET, next to the missing spring:



MANY people drive for many years without this washer and report no issues at all. It could slightly preload the spring tension, so if it is missing, the belt tension at which the Toothed Belt warning trips could be slightly lower. You could drive for years without the spring as well with the low tension warning effectively disabled.

Finally, I found the reason the tensioner leaked - a nice hole cut in the boot near the bottom. The boot was pliable and not hard and cracked.

worf928

Yup. Sigh.... another way to ensure that pesky tension warning system is always quiet.

I found the same thing at least once.

I have lost count of all the eff'd up belt systems I have seen.

However, the weirdest one was the result of troubleshooting an electrical problem that had nothing to do with the belt. This problem led me to open up a digital instrument cluster. When I did, I found a stray solder ball in one of the multi-pin connectors shorting at least two (possibly four) of the leads together. One was ground. Guess what the other one was? Guess what I had to do next?

This is why the last thing I connect when buttoning-up a belt job (and when doing a tension check or inspection on a system I didn't put together) is the tension warning circuit at the belt cover. I always do the first start with it disconnected and let the car run for a few minutes or until I see the belt warning.

PorKen

Flennor = Gates

Just bolt on a PKT.

the flyin' scotsman

If you need some parts Bill I know where there is a tensioner or 2 lying around

borland

Yes, sell the factory tensioner and use the proceeds to buy and install the PKT. When you add up all the parts and subsequent retensioning labor, it just makes sense.

GregBBRD

Put in the spring and washer, when you pull the tensioner and replace the boot and gasket.

Sometimes I wish shops would just put all the stuff they don't know know what to do with in a little box in the back of the car, so it doesn't takes so much time to find the stuff they leave off.

Want to bet the inside "circlip" for the boot is missing, too?

leperboy

I tore two of those boots the first time I tried to do my timing belt job. Gave me the privilege of doing the job three times. I tore mine trying to fit the tensioner back in once I had rebuilt it. I can't remember the particulars, but once I got it right I realized how stupid I had been in how I tried to get it on the first two times. The tear looked the same as that.

Matt

soupcan

Both my 83 and 86.5 had the spring missing, here is the kicker....both had their 60,000 mile service at the same dealership.

fbarnhill

Bill, I have a couple sets of the tensioner arm, spring etc from an 86.5.. They are yours if you want them, just let me know.

Thanks,

PorKen

Tension sensor starts in '85.

Bill Ball

Hi Frank: I've got everything ordered except that wire clip on the boot center that Greg bets is probably missing too - I need to go out and check that now.

Back from checking that...Whew! At least they didn't lose that part.

soupcan

You are correct Sir!
Strike 2 on the thought I have too many 928's, first I got my keys confused the other night and now I can't remember basic 4.7/Euro S/S3 and S4 differences!