Author Topic: Stripped inlet thread  (Read 3132 times)

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Offline phil_h

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Stripped inlet thread
« on: 31 Aug 2009 at 22:02 »
Well, the good news is that the engine is back together on my '13 (model R according to the '88 register - eng 11570) and it starts and runs ... after a fashion.
The bad news is that its almost impossible to get the front inlet tube sealing.
Unfortunately it looks like its the thread on the head thats worn too.
Suggestions would be most welcome.

Additionally, the timing check (?) bolt on the top of the front cylinder also has a poor thread.
Is that one of those dodgy 25tpi threads or a more ordinary 26tpi cycle thread ?

I would also like recommendations on the best plugs to use too, as the ones fitted are short reach and look very sad fitted to those quite deep bosses.

regards
phil

Offline Alan Cun

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Re: Stripped inlet thread
« Reply #1 on: 04 Sep 2009 at 08:11 »
Hello Phil, I have come across this problem several times. The first way of repair I chose was to cut the intake section off and braze a serviceable piece from another barrel that was beyond its future usefulness.

My next approach was to make up new lock nuts that would be increased in length by about 3/16 inch. This allows the thread to engage further down the intake thread which is usually still serviceable.

I went searching in the scrap and came up with an old Norton Roadhoder stauntion which had the perfect inner and outer diameters to take the 20 tpi tap. It was just a matter then of welding a washer drilling out to manfold diameter. Cut the 4 C spanner slots with an angle grinder.

That was my solution anyway?????????????   regards Alan

Offline phil_h

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Re: Stripped inlet thread
« Reply #2 on: 04 Sep 2009 at 19:43 »
Hi Alan
I like the casual way you say 20tpi tap  :lol:
It does sound like a good plan though to make longer collars, so long as I can find a suitable tap !
If only you were a bit closer and I'd post you a length of tube to tap for me :wink: - I've got an old bent commando fork tube that might do, or if not that, several velocette ones (I race them).
Everything I've done with motorbikes this year has started well than taken a quick turn into a hidden ditch :(

phil

 

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