Excess SC Tensioner travel? Is the chain stretched?

[rtuey]

Starting another thread to discuss my discoveries after dropping my '82 911SC engine. With > 235K miles, I am looking at putting in the Carrera tensioners. I measured the tensioner piston distance from the lip of the tensioners to the sprocket lever: 14.5mm on left side; 11.3mm on right side. The small picture in the Bentley's seem to have a much smaller amount of piston showing.

Attached is a picture of the tensioner, and the chain ramp which is slightly broken. (I found debris in the sump filter which seems more than what is broken off in this visible ramp.)

Questions:
1) Is is evident that the chain is stretched and needs replacing?
2) If it must be replaced, can I do this without having to readjust the cam timing?
3) How hard is the chain replacement? I'm told the trick is to maintain tension on the chain; remove a link; put in a master link that attaches to a new chain; rotate the new chain through the housing until you can remove the old chain

4) Is it possible to replace the chain ramps without cracking the case? I can't see how you would remove the left side, lower ramp. Picture is attached where you can see it chewed up on the left side.

5) Another non-sequitor question - Is it OK to buy a cheaper clutch cable from Vertex or Automotion ($49) rather than the Gemo cable ($76) from Pelican? Current cable is Gemo, and lasted 235K miles - until I managed to damage it removing it as part of the engine drop.

As always, your advice is appreciated. p.s. - pictures attached as evidence that I really did do a drop - my very first, albeit with help and advice.

[smdubovsky]

Try to lift the chain off the cam pulley at the far left of your first pic. A (badly) stretched chain & sprocket will lift off the teeth. If you think about it, the tension is held by the first tooth in contact w/ the first pin on each side. So about 180deg of the chain/pulley are doing no work. A stretched chain will have a pitch line longer than the pulley, and a worn pulley will have a smaller one. The two together will create some slack. Note: even a new chain has a little slack. This procedure is documented in the factory manuals & pelican book IIRC.

Im not sure 14mm is all that much to worry about. Replacing some of the ramps will take up a little of the slack. I kept the SC tensioners on my full rebuild and added hydrastops (IMO, a more reliable soln.) Even w/ a new chain & ramps there is enough shaft showing to put them on w/ some room to spare IIRC.

I also think worrying about the chain @ >200k miles is possibly a little nearsighted. Worry about the stuff like the int shaft bushings that you CANT see that are likely quite worn. You know, the stuff you have to split the case & do a complete rebuild for :P VERY Slippery slope you're teetering on:) IMO if you aren't doing a complete rebuild, fix the easy stuff plus the stuff you KNOW is bad and just dont worry too much about the rest. Just saying don't pour a ton of money into it if you don't go whole hog. Just my opinion.

You can replace the ramps you can see (like the one in the pic.) They just pull straight off. 99% you will break the clips off the old ones so dont let them fall in the case! Look at a new one too see what I mean. Its been a LONG time since I rebuilt my motor but I dont think you can replace the other two. Esp if there is a chain in the way. I put one of the ramps on backwards and had to partly disassemble to flip it right. Didn't need to resplit the case but IIRC a good amount of stuff had to come back off.

[rtuey]

Thanks for your thoughtful post. You are right, I don't want to go down the rabbit hole. I like the hydrastop idea. Would you highly recommend putting in new SC tensioners rather than the Carrera upgrade, or can I just reuse the existing ones? I thought I saw something about a rebuild kit for them, too. They haven't failed.

Cost is becoming a bigger consideration, as the DoD weather satellite system contract I'm working on was just zero'd in the Defense appropriation bill signed this weekend. My new year's gift was my contract will likely be recompeted and I'll probably have to find another position (though I think I may be well positioned to do so).

In any event, I'm definitely doing the clutch, and the engine is already much shinier and less oily. Who knew the black heat exchanger elbow is really silvery.


Try to lift the chain off the cam pulley at the far left of your first pic. A (badly) stretched chain & sprocket will lift off the teeth. If you think about it, the tension is held by the first tooth in contact w/ the first pin on each side. So about 180deg of the chain/pulley are doing no work. A stretched chain will have a pitch line longer than the pulley, and a worn pulley will have a smaller one. The two together will create some slack. Note: even a new chain has a little slack. This procedure is documented in the factory manuals & pelican book IIRC.

Im not sure 14mm is all that much to worry about. Replacing some of the ramps will take up a little of the slack. I kept the SC tensioners on my full rebuild and added hydrastops (IMO, a more reliable soln.) Even w/ a new chain & ramps there is enough shaft showing to put them on w/ some room to spare IIRC.

I also think worrying about the chain @ >200k miles is possibly a little nearsighted. Worry about the stuff like the int shaft bushings that you CANT see that are likely quite worn. You know, the stuff you have to split the case & do a complete rebuild for :P VERY Slippery slope you're teetering on:) IMO if you aren't doing a complete rebuild, fix the easy stuff plus the stuff you KNOW is bad and just dont worry too much about the rest. Just saying don't pour a ton of money into it if you don't go whole hog. Just my opinion.

You can replace the ramps you can see (like the one in the pic.) They just pull straight off. 99% you will break the clips off the old ones so dont let them fall in the case! Look at a new one too see what I mean. Its been a LONG time since I rebuilt my motor but I dont think you can replace the other two. Esp if there is a chain in the way. I put one of the ramps on backwards and had to partly disassemble to flip it right. Didn't need to resplit the case but IIRC a good amount of stuff had to come back off.

[smdubovsky]

You're going to have to do your own research on carrera vs SC tensioners. About 10yrs ago when I was rebuilding some of the pros started recommending the hydrastop route. There have been carrera tensioner failures too. The arm is what usually failed on the early cars. That was updated on the SC (same as carrera) so all that should be left as a problem is the tensioner itself. W/ the hydrastops, if the tensioner fails the chain will just get noisy but not skip a tooth. Thats my kind of reliability (lets me know its broken but nothing goes kablooey.) Plus they're really inexpensive and a couple less places to leak oil:)

Edit: Im not saying to not replace the chain. If its worn, replace it. If it still tests good, then I'd let that sleeping dog lie.