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New RH5 Commando head, bad exhaust thread

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New RH5 Commando head, bad exhaust thread

Posted by benedict_spencer at April 05. 2017

I bought a brand new Commando 750 RH5 head, (I know, rarer than hen's teeth) but brand new it is. Five for sale and they went in hours, I got the last one.

All has gone well but the exhaust port threads are not cut properly and the nuts don't thread far at all.

Has anyone got a tap to cut the threads properly? I can borrow and return with some form of folding appreciation?

Or good ideas?

Re: New RH5 Commando head, bad exhaust thread

Posted by john_holmes at April 05. 2017

You could try the outfits that repair worn threads and see if they can cut your undersize thread.

Mick Hemmings is still doing work but not selling parts and he does welding and then recutting so you only need his recutting.

http://www.seager-engineering.com/index.php repair Norton and Triumph exhaust port threads by using an insert which they cut after its in the head, so again you just need the recutting.

Re: New RH5 Commando head, bad exhaust thread

Posted by robert_tuck at April 05. 2017

If bought from Norville perhaps the undersize Norville nuts fit?.

Re: New RH5 Commando head, bad exhaust thread

Posted by benedict_spencer at April 06. 2017

Thanks for the replies.

 

Other off line suggestions include cutting slots in a nut, hardening it and using it as a tap to chase out the thread.

 

See http://www.accessnorton.com/norton-exhaust-thread-chaser-t12513.html

 

Re: New RH5 Commando head, bad exhaust thread

Posted by john_holmes at April 06. 2017

If you go that way then take off the first 2 threads completely so there is a decent pilot to get it started straight and then follow up with a second unpiloted one to cut the last 2 threads. I have used this option to recover a thread in a Triumph head using a 15 thou over exhaust insert and then fitted a 30 thou over insert which went in snug. The 850 nuts will be too short, best with 750 nuts.

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