It's rude to spit!

[72degrees]

The 2C/375 was given a good cobweb blowing out on Sunday. It was going very well. So well that I had it literally "off the clock" (well it is only a 250 speedo). Unfortunately as revs returned to something more befitting a motor that hasn't been apart for over twenty years a familiar noise became apparent. If it had been even more familiar I would have stopped in time, but as it was by the time I found a safe place to pull over the exhaust collets had been spat out and the front pipe was almost out of the port. Luckily the nut/ ring thing stayed on the pipe and with the aid of a half brick as a hammer and an open ended spanner as a drift it was persuaded to stay in position long enough to get noisily home. I had checked the tightness three times after putting the 2:1 system back on following brazing it up to repair the Cadwell induced fracture, but I hadn't bothered to wire them up as I usually do.

I'm hoping that the threads in the port have survived enough not to need reclaiming and that NLM have the collets in stock or I'll be asking you all to look in your box of left over bits for some.

[Richard A]

Ouch! I read that as exhaust valve collets, and was wondering how you limped home. Then I read your post properly. Think I'll check mine.

[72degrees]

Ouch! I read that as exhaust valve collets, and was wondering how you limped home. Then I read your post properly. Think I'll check mine.

Heh, I probably should have said "half rings" as that's what NLM call them. Fortunately they have all four kinds in stock. It was revving pretty high - the tacho is also a 250 one , but the special Weevee alloy valve spring caps I fitted years ago coped OK.

I remember seeing years ago some cunning clamps that went on the pipes just before the castellated rings and had a bit that went between the castellations to stop the rings unscrewing. Much neater than wire. I *think* someone came back from a visit to the factory with them fitted.

[John Bunting]

Hi 72,
"Off the clock" it sounds like you were being a naughty boy and expeeding the seed limit, losing the exhaust half rings is the newly introduced penalty
Wire the lock rings racer style
John

[72degrees]

Hi 72,
"Off the clock" it sounds like you were being a naughty boy and expeeding the seed limit, losing the exhaust half rings is the newly introduced penalty
Wire the lock rings racer style
John

I plead the fifth - well sixth actually as it's geared down one tooth on the gearbox sprocket. The half rings arrived today. Look different to the ones it had before but as if the will fit better. The thread seems not too bad. I will certainly be lock-wiring the rings this time!

[EVguru]

There were several designs of exhaust half-rings, the early ones for example being Bronze and having a tapered face.

Some bikes seem to have a problem with exhaust nuts coming loose, whilst others don't. Morini used a close tollerance metric thread, but some port repairs have used metric standard (not NLM!) and the nut rattles.

The most elegant way of preventing the nuts coming loose is one I think the factory applied to some Kunguros. A stainless pipe clamp with a tab added to engage with one of the castellations.

[72degrees]

To be fair, the fact that a 350 2:1 system is fitted to a 350 motor in a 250 frame doesn't help. Joint between the pipes is very close to the frame and an adapter is needed for the silencer mount. Everything is in tension and that's probably why the fracture just before the 'megaphone' happened at Cadwell. The repair I did relieved that a bit but there is still possibly a bit of pull on the front pipe so any loosening soon progresses.

I don't suppose those Kanguro locking clamps are available anymore. It ought to be possible to fabricate something similar with access to the right welding gear. Stainless lockwire from castellated ring to a head fin has worked for me in the past though. The bike is hardly elegant anyway

[72degrees]

Curses. The thread is worse than I thought. To be fair it is an original 76 head that has seen a lot of engine and exhaust system swaps. Only a small amount of good thread left in the very base of the port so with a new gasket and the correct half rings I just can't quite get it to bite well enough to risk even when wired up. Oh well, the head has a bodge on one rocker cover stud and I can always use a head off the spare motor if I want to keep it running while this one is being reclaimed. Better make a start I suppose.