Timing and oil pump schain stretch limits

[szacsi72]

I've been digging the interwebz and the forums for an hour with no luck.
I would really like to find some data regarding when to replace a timing chain. My engine has had a questionable life; it was rebuilt before me and milage is unknown. To my eyes, both chains look intact and there's not a lot of wear visible on the gears/sprockets.
I would like to get some numbers... so that I can measure their stretch. I don't want to pour more money into the rebuild than needed, replacing a chain that may be perfectly fine is not an option.

Thanks!

[Mike W.]

I have heard, or likely read, that timing chains don't stretch, or wear in such a manner that causes them to be longer. They do wear, presumably on the rollers and the pins the roller ride on. I almost think you would have to have it assembled to measure the deflection in the chain. The BMW factory manual may say something, especially the E12 one which seems to give more specs, and which I have, both paper and electronically, but I'm not at home.

I haven't bought one in a while, and everything seems to have gotten much more expensive, but last I knew they were cheap. I"m cheap and don't throw money on unneeded parts and I just replace them if I'm in that far.

[Aldo525]

I understand the same thing that Mike mentions, the stretching is due to wear of the rollers and, unless it is very worn, the chain should not be changed. In my case, I changed the chain on the M10 engine (e28 518i) for safety but it was not in bad general condition. But when assembling the new one I realized something that I didn't see evident: the old chain was so "stretched" that the tensioner no longer had much more tension range, that is, it was close to no longer tightening any more and there the "chain noises" would begin. So my conclusion on this is to check how much more tensioner travel there is left for the chain to be loose.

[ccchrisss]

When i changed my timing chain, there was a noticable difference in tension. The old one was quite loose, didn't measure the deflection but it was very easy to remove. Putting the new chain on had almost 0 deflection, it was tight and a perfect fit. Even with the stretched chain the engine was running fine, only changed everything because I was already in there to remove a broken guide rail. This was at 170k and looked like an original chain and sprocket. As long as the teeth on the sprocket aren't heavily worn I was told that it would still be fine to continue running.

[Galahad]

It should be a standard chain size, I'd assume metric. Should be able to measure the length and find out.

Something I didn't see mentioned is that chain stretch will retard the cam timing, so at a minimum I'd check the cam is at TDC when the crank is.

[szacsi72]

The only chain I can get in Hungary is a FEBI brand, 44294, which is S94E-G68V/G68WN. Judging by the pictures it's an iwis chain.
This means:
Simplex, 94 link, endless, 3/8" chain.
I guess I'll try to measure something like 30 links to see what I get.
Also, you guys meantioned wear. I think I should be able to measure the rollers in the middle and on the sides and see if there's a difference.

[szacsi72]

It should be a standard chain size, I'd assume metric. Should be able to measure the length and find out.

Something I didn't see mentioned is that chain stretch will retard the cam timing, so at a minimum I'd check the cam is at TDC when the crank is.

That won't work, my head and block are getting decked quite a lot. But I'll run an adjustable cam gear.