S38 timing chain assessment

Post here for mechanical and engine topics such as fuel issues, transmission problems, rough idle, exhaust, electrical issues, etc

Moderators: GRNSHRK, ron, bfons

Post Reply
User avatar
Bhart
Bigcoupe Contributor
Bigcoupe Contributor
Posts: 141
Joined: Fri Sep 25, 2015 10:24 am
Location: Ontario, Canada

S38 timing chain assessment

Post by Bhart »

It's time for me to do some service work on my '87 M6 S38. I have struggled to find any details in the limited documents I've got from the POs but there does not seem to be any record of a timing chain replacement. It's got 147,000 miles on it and runs well, uses no oil (will do leakdown before service) and I need to do a valve adjust (or at least check clearances) and a service to throttle assembly (sticks when engine hot) so I'd like to know if there's a way to assess the state of the timing chain and chain guides easily on this engine.
01/1987 M6

past Bimmers;
1970 2800CS
1988 325is
1985 325E
User avatar
sharkfan
Platinum Member
Platinum Member
Posts: 2235
Joined: Tue Sep 28, 2004 3:14 pm
Location: Guildford, U.K.

Re: S38 timing chain assessment

Post by sharkfan »

If it's an American spec 'M6' with 256bhp then it is indeed the S38B35 engine.

Euro/rest of the world got the 286bhp 'M635CSi' cars with the M88/3 engine.

The critical difference is the type of engine; like the E34 3.6 and 3.8 M5's with their S38B36 and S38B38 engines the S38B35 has a double row timing chain which significantly reduces chain whip, chain, chain guide and sprocket wear so should only need a replacement timing chain, guides and sprockets if you have the engine apart for a major rebuild for another reason such as increasing power or bearing/piston-ring/all hell has broken loose failure.

The M88/3 in the E24 M635CSi and E28 M5 has a single row chain which is known to stretch, wear and ultimatly fail and does need a precautionary age or mileage replacement.

You should be fine unless you can see signs of wear on the sprockets, guides or chain, or you can hear any chain nose or whip.
2001 Alpina B10 V8 Touring (1 of 12 rhd)
1997 Alpina B12 5.7 L (1 of 2 rhd)
1995 Alpina B10 4.6 Touring (1 of 1 rhd)
1985 BMW M635CSi (1 of 524 rhd)
1982 BMW 635CSiA (1 of 100's left from the 1000's made and still valiantly fighting against a rusty grave)
User avatar
Bhart
Bigcoupe Contributor
Bigcoupe Contributor
Posts: 141
Joined: Fri Sep 25, 2015 10:24 am
Location: Ontario, Canada

Re: S38 timing chain assessment

Post by Bhart »

Thanks Sharkfan.

Yes, an American spec car, delivered in Massachusetts (had to spell check that) and now in Canada.

The leak-down will tell a lot on the condition of the entire engine - look forward to knowing that. When I pull the cam cover, I'll have a close look at the sprockets for uneven tooth wear and see if I can peer down to assess the guides.

Is there any service or maintenance that should/could be done to the hydraulic tensioner from outside?
01/1987 M6

past Bimmers;
1970 2800CS
1988 325is
1985 325E
User avatar
Da_Hose
Platinum Member
Platinum Member
Posts: 3236
Joined: Fri Mar 07, 2008 8:15 am
Location: Santa Ana, CA.

Re: S38 timing chain assessment

Post by Da_Hose »

If you look up my threads, you will see what my guides looked like at 135K. I agree with Sharkfan. You might not need a replacement, but if the engine is apart, do it. It is false economy not to. If you are doing general maintenance, I highly recommend upgrading your tensioner. I believe the worn guide, in combination with weak tensioner lead to my needing a top end rebuild.

You should be able to get a scope down to the tensioner when the valve cover is off, and get an idea how worn it might be. Look at the side, and see how recessed the chain is into the guide, to get an idea of wear.

Jose
1987 M6 - My dream car
Post Reply