UKKid35

I have just completed another TB change, this time at 35k, the previous change was slightly less.

My sprockets are now completely worn out, not just the cams, the worst of all is the oil pump, and even the steel crank sprocket is showing some wear. The old belt itself is is perfect condition, no sign of any damage whatsoever, and absolutely no sign that the teeth are about to be sliced off - I know what that looks like unfortunately.

I can't justify spending over a grand on a new sprocket set, so I'm going to reduce my belt change interval to 25k (which will be significantly more than five years).

The belt change itself has gone well, I'm only aware of making one small mistake.

I used my preferred method of removing the crank bolt, the starter motor, and that took seconds. But I'd forgotten how difficult it can be to remove the balancer, at least I don't have the even more awkward prospect of removing the crank sprocket.

I did eventually remember how to use various size sockets in order to swap the bearings in the idlers, I'm glad I did that. I am also very pleased that I bought some relatively expensive 'Engine Assembly Lube', it makes those sorts of jobs much easier indeed, it's much better than simply using LM Grease which is what I used to do.

I took my own advice and swapped each waterpump bolt in turn for a new one, even though I'm not replacing the waterpump this time. But since they were all nicely greased up from last time, not one presented even the slightest problem, I still took the precaution of using a T-bar though. I did double check the 8Nm torque setting as I know how easy it is to break WP bolts.

I also managed to rebuild the tensioner without issue. This is the first time I've done that job and found the rubber boot fully intact and still supple, and the tensioner full of oil.

I got the belt on correctly first time, teeth aligned perfectly, which was very satisfying.

I'll be refitting the cooling system later today, and then heading off to the Nurburgring tomorrow.

FredR

Some observations if I may-

Your first photo of the front of the engine fully stripped presumably is taken with the motor at 45 BTDC. You have some red indexing marks on the front of the sprockets to advise you where the sprocket teeth were compared to the notch in the back casing before you removed the belt. When you finished the job did you turn the crank to TDC and check that the index mark on the back of the sprocket aligns with the notch in the casing? Difficult to say with certainty from your pics but I get the impression that those index marks are more like 4 teeth pitches away from the casting indent. No desire to be alarmist - just a cautionary check if not done so already. If th sprockets are out a tooth it will do no harm but it would retard your cams helping top end a bit at the expense of low to mid range torque. Hopefully it is just an optical illusion caused by wide angle lenses.

I am struggling to understand your correlation between worn sprockets and belt change interval. If the sprockets are worn to the point of being capable of causing belt damage then they need to be changed much as it hurts the wallet. As to what degree of wear is needed to cause belt damage is the real question and it is not one that needs to be determined the hard way. As I understand it is a "cliff edge" type of thing - OK to a point and then wham- they cut through in no time. I suspect there is some degree of conservatism in the 928 community about this but given the potential consequences that you clearly understand how lucky do you feel? If nothing else I would be taking a good look at the belt condition regularly [every 5k miles?] but I would not sleep easy - your call of course.

Why do you loosen the crank bolt with the starter motor? - is it because you do not have a nice big lever arm to get it undone?

I was also a bit puzzled as to why you would have a socket on the cam bolt locking nut given you did not remove the cam sprockets. I liked the use of the bulldog clip to hold the belt onto the 5/8 sprocket whilst feeding the rest of the belt - FYI I use a zip tie or an extra pair of hands that I never seem to have on hand.

If you loosen the crank nut with the starter motor how do you turn the crank to get it to the 45 BTDC position for belt change? Similarly, how do you tighten it?

I also noted that rusty looking surface deposition on the top hose nozzle- is that what you normally see in there? What coolant change interval do you apply?

Wishing you a great trip to the Nurburgring.

UKKid35

Thanks Fred, you make some very good points.

The reason the red 45 indexing marks on the Cams are not exactly aligned with the backing plate indents is because it is effectively impossible to remove all slack in the belt between the crank and the odd bank cam, therefore to compensate for this the cams are turned clockwise about half a tooth. This is the natural state for the odd bank cam, but to rotate and hold the even bank cam I used socket as you pointed out.

Sure enough as soon as the crank is turned the tension is taken up, and everything lines up nicely at TDC, repeatedly.

I think you are right, there may well be a cliff edge (knife edge even) situation with the cams, and although they do not have sharp edges yet, the teeth are dished. Having had the opportunity to study the belt that came off the car 14 years ago, I think I would be able to spot the alarm signs, but of course I could be deluding myself.

I do indeed keep an eye on the mechanism pulling the cover and checking condition and tension at least annually. I don't get to see the state of the oil pump sprocket though unless I do a belt change.

I would not have slept easy knowing I was heading off to the Ring without changing the belt, as I had previously vowed to keep to a 30k internal, and I had let it slip.

I use the starter motor because it is quick and painless, and once the pulleys are off, yes the bolt goes back in, but it can be removed again using a quick action with a wrench rather than sustained torque. To tighten I use a breaker bar, fifth gear, and GF stamping on the brake pedal.

I use long life coolant, and change approx every four years, once car has been exposed to rusty coolant those stains never seem to go away - and sure enough the car was a model of deferred maintenance when I bought it fifteen years ago.

I will be sure to share pics and video from the Ring, I always do!

FredR

OK- first point you have a manual tranny- tend to think all S4's have auto trannies but of course that is not the case for the earlier S4's.

If you are using the socket on the cam sprocket to put a bit of tension on the belt no problem but as an FYI- the general consensus is not to try turning the cams using the 17mm nut- do so on the larger 30mm or whatever washer. You are probably aware of this but just in case.

I highly recommend you acquire a crank locking tool and the 32VR cam timing kit unless you want to time your cams using dial gauges. I did mine with gauges and then acquired the 32VR kit so knew for sure that the calibration was spot on. I recently changed my cam wheels and setting up the timing took 10 minutes and 5 years to put everything else back [actually I got eveything else back on in an afternoon]!

There is a general consensus that changing coolant every 2 years is a wise thing. I now follow this but then I do not have a wide choice of top quality coolants. Previously I used to do mine every 4 years but then I used Redline water wetter and after 2 years I would drain some coolant off, and add another bottle of Redline more becuase of its fresh anti corrosion chemical package. Plenty of debate on the subject historically.

Regards

Fred

UKKid35

Sadly my trip to the Ring is not worth a separate thread, so here are a couple of photos from the day.

No video this time as the GoPro was being moody.

And worst of all I only had one hour of track time before the heavens opened. I can't drive in the wet, and I'm not going to try to learn at the Ring...

UKKid35

For some reason pics are not displaying in Chrome, but they are using Firefox - weird.

Wisconsin Joe

Work for me in Chrome.