Forum bmwbike.com

Does anybody know how the thread on the cylinder head that holds the exhaust coupling nut can be renewed? The one on my bike (R25/3) is totally worn out.

Any feedback is highly welcome.

Hi Christian
We weld them up and recut the thread. I know that there are many who fit threaded collars or inserts but I am dead against this. The threaded collars remove so much aluminium that the flange is weakened and will brake of in time. The inserts are usually turned out of cast iron (due to thermal expansion coefficient) but also loosen though they are additionally rivetted and are extremely rust prone due to the extreme temperature differences etc.

We have forged aluminium exhaust nuts with cooling fins like the R69S etc for the 250cc singles. We highly recommend these as alu on alu with a film of Copper-Slip in between will last forever without doing any damage.

Best regards,

Mark
Mark Huggett GmbH

Hi Mark
Thanks for the very quick reply. How do I have to understand the part about the forged aluminium exhaust nuts with cooling fins? Could I avoid the welding job by placing the film of Copper-Slip in between the nut and the old thread? What is the part number of the nut w. cooling fins?

BTW, the bike runs really nice with the new valves.

Best regards,

Christian

Hi Christian
Part no. for the finned aluminium forged exhaust nut is 18 11 4 000 002.
There is no shortcut around having the thread repaired. The copper-slip is purely an anti-seize high temperature grease to avoid the two parts corroding together or seizing. Be aware that the nut is also aluminium so if you force it on as you have done with the steel exhaust nut, you will also damage the thread of the nut its self. Christian, I can only advise you to take no chances with this job, no short-cuts and no compromises when looking for a workshop in your neck of the woods to weld up and recut the fins...I've experienced almost all
that there is with BMW cylinder head repairs and seen almost everything possible. What might appear to you to be a good alternative and cheaper or
easier repair, you will regret later,...maybe 2 months later, or 2 years later.

Re alu-welding and machining...get hold of the local Yellow pages and look under aluminium welding, welding, aircraft repairs.

Best regards,

Mark
Mark Huggett GmbH

Hi Mark

I had the alu-welding job done and am very happy with the result. Theu did a professional job that came at a price: The Peso equivalent of 100 U$. From what I know, this kind of job is offered in Germany for DM 90.

Anyway, thanks for thwe help!

Best regards,

Christian

Hi Christian
The DM 90.00 jobs in Germany are terrible. I know that they are advertised, and I've seen the work. The professionals have a jig which is permanently set up in a lathe specially for BMW cylinder heads, and the machine does nothing else. Your USD100.00 job is very cheap considering that it is 1 cylinderhead which has to be set-up, aligned and held in place twice in a row, i.e. once to turn off the old thread, then removed to weld, then set up again to recut the thread....do you know how much time and work is involved? To give you an idea, if the job cost you USD 100.00 in total, USD 5 was for welding, USD 5 was for cutting new thread, and USD 90 was the shere time spent setting up the machine twice, just for one cylinderhead.

Regards,

Mark
Mark Huggett GmbH