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fork thread size


Having trouble with the thread on the crown lug even with a new adjuster nut for the head bearing from n o c . It is unbelievable how both old and new nuts are so tight. I was thinking of running a die down but not sure of the thread size I believe it is 3/4 in pipe. There are 3/4 split dies on the market but different thread sizes not used a split die before are they adjustable!  Thanks Bryon.


I doubt that the thread is pipe thread.  It's probably 20TPI cycle thread. 

Have you considered the careful use of a thread file?

Much cheaper than a die and multiple use. I have repaired many crucial threads where a previous owner has been a bit enthusiastic with a "Tappometer". I am the worst offender for having to have every tap and die but so many are only single use.

It is probably only one area of thread that is slightly tight, so worth a go.

I have never used a thread file the adjusting nut is about 1 I/4 long and the pipe thread about 2 1/2 in long it gets very tight with the nut just 1/2 on. I will check on a thread file. thanks Bryon

Just check the TPI. It may be 20 but possibly 26. Borrow a 1/4 inch bolt from a mudguard , an original one. Match the pitch of the bolt with the thread on the stem. If they match, it will be 26.



Just to be clear here - are we talking Jubilee or Navigator/Electra?

It will be 26TPI irrespective - only Commando used 28TPI.

Thread file. Its a long time since I found one with 26TPI - Cycle & Whiteorth thread forms. Does anyone know where I can get a new one?

It is an Electra that as had a hard life it had 19 ball bearing in each race with Bruce M S manual calling for 18 if that is a clue. I will make sure it is 26 TPI and then search for a thread file Thanks Bryon

Just received a Whitworth thread file with 26TPI  along with other sizes. They are made in England by Sykes-Pickavant  got it from our local dealer Motoparts  Bryon


The Norton Mercury used quite a number of Commando parts and its stem (Crown & Column) probably had a 28tpi thread as well.


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