Bit of a puzzle

[r75bitsa]

G`day all
R75/5 with an R100 motor, /7 seat tank and wiring loom with other easily sourced later model stuff.
Very close to club rego, cleaning up the fiddly bits that usually get left to last.when getting the throttle cables right and giving it a bit of right wrist, i`ve noticed a puff of smoke (haven`t quite got the mixtures right yet) from the left hand exhaust at the joint to the head.

I`ve tried the little compression ring thingies both ways, though the latest one has almost solved the problem, its still there. Clamp screwed up nice and firm stainless engine pipes from the old /5 stainless mufflers. Barely felt at idle, still noticeable when giving it a rev. Is there a difference in the pipe sizes at the head? Manuals are no help. Its a `78 r100 motor runs well apart from this headscratcher I`ve got the split ring at the top this time round.
Regards to all

[Kurt in S.A.]

I don't think the split in the ring has to be in any direction. But this particular joint consists of two parts...one is a non-split ring with a bevel in it, the other is the split ring which has the reverse bevel in it...#8 and 9 in this picture:

http://www.realoem.com/bmw/enUS/showpar ... Id=18_0268

Hopefully you have both. Once the exhaust nut is drawn up tight, the two rings work together to make a seal. The header pipe also has to be fully seated into the exhaust port.

Kurt in S.A.

[r75bitsa]

I'll give it another go, see if it will seat any deeper
felt like it was at the end. I was wondering whether there was any particular orientation to those rings when they are on the pipe.

[SteveD]

Compression ring is the outer ring. It pushes on the split ring. Try swapping the split ring to the other side and see if the puff of smoke moves with it. I had that once...a new split ring fixed it.

[SteveD]

The header pipe should be the same unless your 78 is a 40mm exhaust?

pn 18111230433 Exhaust pipe, right. D=38mm

Part 18111230433 was found on the following vehicles:

R50/5-R90S 69-76   (08/1969 — 07/1980)
R 60, R 75 , R 80, /7, RT (76-85)   (05/1976 — 01/1985)
R 100, /7, /T, CS, RS, RT, S (76-84)   (03/1976 — 11/1984)

[Airbear]

G'day Bitsa. I chased the same problem for far too long. The split ring on one pipe was simply too large in diameter - possibly from a 40mm pipe. A few bucks thrown at Shiny New Parts fixed it.

[r75bitsa]

Mmmm, thanks guys, sometimes you wonder whether you're the only one with a Pia problem. This has been a head scratcher for too bloody long. Chasing it when you have the time and still it persists. One more go, and then down to phils and some brand newies. Thanks again.
Regards to all.

[r75bitsa]

Will have to take a pipe measurement today, though the rings move fairly well over the pipe when moving them into position. Fairly sure they are 38's.

[r75bitsa]

October eh.
Life gets in the way doesn't it. Tried a new set both sides that phil graciously provided, no dice. One option is suitably sized copper gasket that look like they'll do the job, yet to see. Others have said use "heatproof silastic"???. Anybody heard of or used it.

[Rob Frankham]

I think it is most likely that your headers are 38mm but your heads are machined for 40mm headers. Assuming this to be the case, it is unlikely that you will achieve a perfect seal using stock components. If, as I surmise, replcement headers aren't an option, I would suggest the best bet would be to make up shims to go around the headers into the heads. 1 mm stock shim metal should do it. Fitted with exhaust paste, that should provide a good seal.

Rob