Re-build Experts chew on this one!

[Gunter]

3.0 Liter US top-end rebuild 2 years ago, new chains, but not new chain sprockets on the I.S. Runs beautiful for about 15K Miles. During oil change, many teeth are found on the oil stainer. Boroscope reveals that the teeth are coming from the I.S. chain sprockets. Tear down to replace new sprockets. I.S. gears are perfect, shell bearings perfect, parallelism right on, no wear on ramps, tensioners, or cam sprockets. No sign of any damage or misalignments. Somehow, the old chain sprockets did not tolerate the new chains and wore the teeth to a point where they would break half-way. This engine showed no signs of misbehaving, no noise. If the owner would not have taken the oil strainer off, this engine would have run until the chains would have jumped with disasterous results. My friend has re-build many Porsche engines but has never seen this before. My experience in industrial applications cannot acount for this other than that the new chains did not fit onto the worn tooth structure of the old I.S. sprockets. It seems to me that when an engine has about 200K Miles, not just new chains, but also new I.S. sprockets are in order. So, whoever wants to just feed a new chain with a M.L., consider the above. Any comments?

[HawgRyder]

I have seen this effect on motorcycles.
The chain slowly stretches....the teeth on the sprockets get worn to compensate the increased distance of the roll pins of the stretched chain....
.then a new chain is applied....the distance of the roll pins is smaller...and as a result the rollers hit the tops of the sprockets instead of falling into the valleys.
This puts lots of strain on each point of the sprockets...and next thing...broken pieces of teeth in the sump.
Rule of thumb for bikes....new chain...new sprockets....or at least check the old ones VERY carefully.
Bob

[Gunter]

Thanks, more input, please.

[speeder]

Well, that's a new one. I guess that my only comment would be that a good visual inspection of chain sprockets should reveal this type of wear if you know what you are looking at. Glad to hear that it was caught before it grenaded.

[Mikey D]

If you replace one, replace the other. Like previously mentioned, during use the chain and sprockets wear, simultaneously over time. If you replace one, then you will have a brand new unit trying to mesh with a worn one. This is not a good situation. If you replace any part that interlinks with another in such a way that there are splines or teeth, it is prudent that both be replaced to provide the maximum interdigitation betweent each device.


Hope this helps.
Mike

P.S. Who rebuilds a engine with 200k on it and cheaps out on the gear anyway??

[RoninLB]

Originally posted by Gunter

It seems to me that when an engine has about 200K Miles, not just new chains, but also new I.S. sprockets are in order.

Well.. It's a good "heads up".. the logic is easy.. I guess I'll use my borescope to keep an eyeball on the I.S... and take the drain screen more seriously.. so far, 50k on a 90k at rebuild/ A-OK, I hope, LOL................Ron

[HawgRyder]

OK....to check a chain and sprockets....
Put the old chain on a sprocket and wrap it all the way around....
Hold the chain together in one hand at one side of the sprocket....try to "lift" the chain off the sprocket at the oposite side.
This checks the amount of "stretch" in the chain and the amount of wear on the sprocket.
When you substitute a new chain for the old...and do the same test...you will notice that the new chain slides back and forth a bit....this is what kills the new chain.
Doing this test will show you that in order to function properly...the chain must be as tight as possible on the sprocket.....the more movement it has....the faster it will wear.
Bob

[beepbeep]

Huh...i don't know much about rebuilding but i tought it was perfectly normal thing to replace sprockets toghether with chains....no?

Anecdotal expirience:
Yesterday i replaced chain on my MTB and left old sprockets in place just so i could dash to bike-shop and buy special splined tool so i could dismount the sprocket. I was surprized by amount of ratchet new chain made on my old Shimano sprocket. I almost believed that somebody sold me wrong chain...

Makes you think, eh?

[Gunter]

I posted this mostly for people who only want to feed a new chain with a master link onto old I.S. sprockets to avoid splitting the case. This short cut with the M.L. will not tell you the condition of the I.S. bearings either. If you have an oil sump/strainer, check it now and then. If you only have a drain plug, see if a small magnet can pick up debris inside. Has anyone else found metal on the bottom of the case?