[Crazy Diamond]

I've heard rumers that one should not change the cam chain without also changing the cams themselves (or at least welding in new sprockets), since the chain and cams wear into each other. Is this true?



I'm asking because I have my cams and tensioner on the kitchen table, and everything looks as good as new. I have a new chain, but I'm not sure if I should install it or not. TIA.

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[Greimann]

I think if you look at the economics of the situation replacing the cams as a preventive measure just doesn't add up. A stretched chain will do more damage than a new one because the mismatch of the pitch will continually wear the teeth on the loaded side, causing them to knife edge and break. A new chain that matches the pitch of the cam teeth will only wear in a small amount until the wear patterns match and then the wear stops. If your cams look good, just replace the chain.

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[Crazy Diamond]

I just put new pads on the tensioner unit. I set the old chain to hang from something, and I let the new chain hang right next to it, and they both appear to be the same length, suggesting no stretch. Given that the chain and sprockets are all visually good, and now knowing the chain isn't stretched, I thought I'd just put the old chain back in there until it needs to be replaced. Maybe then I can do the cams too, or at least new sprockets for the cams. The old bottom tensioner pad was really badly worn - the groove was more than 1mm deep. The top pad was much better but still bad - about .5mm worn. Also there was a chip of the top pad missing...

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[Dave]

Just did pads and new chain here as part of a valve job. Sprockets were fine and I left them alone.

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[BruceWard]

I believe that the "stretch" is unlikely to be noticed without very sensitive measuring equipment.



The most 968 knowledgable guys I know say to replace the chain with the stronger version and that is what I plan to do. As long as the cam sprockets are in good shape I will use them as is. If I feel they are overly worn I will have them resprocketed.

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[Crazy Diamond]

Hmm. I just finished putting the cams back in, but if it needs to come out again then so be it. So you've replaced just your chain, and it's all good? How many miles have you put on your engine since?



I bought the regular Iwis chain. I might try returning it, but I figure if I'm going to refurbish or replace my cams next time around, I might as well use the less expensive chain this time.

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[flash]

we all know that i would change them without question - spend it now, or spend more later - been there, done that with cam sprockets, with some rather unpleasant expensive results, and don't get me started on making the false economics mistake of leaving motorcycle sprockets unchanged



the key factor is the remaining hardness on the teeth - if that is worn, the new chain will wear them out fast - if it isn't, then you'll be fine - the problem is that you cannot actually see the hardness - bottom line, if there is ANY sign of wear on the sprockets, get them renewed if you want to get maximum life



the problem at that point is that you need to change lifters too, because you should never change cams without changing lifters (same mismatching hardness thing), and at that point, you may as well do a valve job



so, it comes down to how much you are willing to spend for a particular expectation of service interval



personally, i would rather spend 4 grand now, be done with it, and move on, than to have to go back in there in 20k miles and do it all over again

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