Previous Owners

[Rex]

Yeah, I believe it was bolts/hex head screws originally. Next time it comes apart I'll likely change them for hex heads.

[RichardL]

I don't know what is original for the machine, but is the carb such a tight fit in the space that you couldn't use studs 'n nuts instead of that motley selection Richard?

....It wouldn't be easy maybe to repair a thread with the head in situ down the line if a gremlin struck 

Yep, my plan,right now, (which may change before coffee that just beeped ready) is to use standard alloy- head carb studs, bought new or made from an old crankcase tie stud cut in half and threaded one end with UNC 18 (because I have the die).

To the point of fixing it while the head is off, I'll think about that over coffee. It would mean buying a 5/16-26 helicoil kit , which would have limited future application after two coils were used.

Thanks for your comments, guys.

Richard L.

[RichardL]

Looked again into the multi-threaded holes. I guess the reason that almost any thread fits is that there is little thread left at all. One thing certain (for the minute, at least), helicoils will be needed. I have BSC 18 coils now. Great if the head was alloy, but it's cast, which is stock at 5/16-26, as already agonizingly discussed. Comes down to deciding if its worth the $70 for the coil kit to keep the head basically original, a condition that will not be recoverable (within reason) if 18 TPI coils go in. There's a question in all of this. I'm wondering what else on the bike has a 5/16-26 thread that might someday benifit from my owning the 26 TPI coil kit. The final-chain adjusting screws come to mind. Anyone know any others?

Richard L.

[groily]

Not many other holes, I don't think, that might need it, but never really tried to count!
You know what, if it were me Richard (which it isn't of course) I'd use 5/16 x 24 UNF inserts, which are presumably much easier to find. No-one can see them after all.
The main thing - and I'm sure you're right to be doing a proper job - is to know the things will stay put.

If you were really in purist mode, you could get someone to make a pair of studs with 24tpi one end and 26 t'other if you have a BSC die, so the spanner size would be 5/16 BSF / 1/4 Whit on the nuts should you have some correct ones. Or, if going for setscrews after all (in extra-super-pure mode), maybe get the man to use hex of the right AF size (if it can be got) for said Brit imperial wrench. But honestly, is it critical? - 'course snot!

[Swarfcut]

Richard. Cheapest option could indeed be a couple of UNF coils fitted by your local machine shop, as Mr G suggests. CEI threads are used as the majority of cycle fixings, but in the end the economics of a kit for low volume amateur use never make sense. UNF is close to the original thread and will be more easy to match a fixing of choice.

 Swarfy.