198 B fork tube top thread size

[paulmac]

Can anyone advise the size - diameter and pitch - of the thread at the fork tube top? Need to clean up a little whoopsie and can’t find the size listed anywhere. Thanks in advance . Cheers Paulmac 

[johnmartin247]

Diameter is 35mm but not sure of the pitch of the thread.

[carl ekblom]

My nut measures 30.8mm so it ought to be M31x1,5. Quite unusual.

[johnjsy]

Hi there Paulmac, I have just taken the top cap off the top of a spare fork, I think it is from an Alpina. The fork tube is 35mm, used on many models, and having taken he spring out, I used a 30 X 1.5 mm tap to see if it fitted, yes, that is the size. If you need to run a tap in to correct the threads, be sure to clean out any particles of swarf that may be produced. Once done, load up an old toothbrush with a grease, water pump if you have it, then starting at the bottom of the thread, slowly unwind anti-clockwise up to the top of the thread. Being a fine thread, this may take a while ! Hopefully this should pick up most particles. Hope this helps ......

 

[feetupfun]

Paul just a thought. I've seen a couple of M199B that have the taper top fork tubes, like a pre-74 Bultaco fork tube. I don't know enough about 198B to know if it's the same with some of them too. If yours is like that it might be a different thread to the tubes with the parallel top tubes. I'll check a taper top tube soon and post up the thread size

[paulmac]

Thank you guys, your help is very much appreciated. Johnjsy great advice ? feet up fun they are parallel but cheers for the heads up. Once again thanks all. Cheers Paulmac 

[carl ekblom]

I think 199B can be made of different things. My 199B top nuts have allen key at top.

Rule of a thumb: Inside female diameter is outside male diameter-pitch. Measured inside the stainchons M30x1,5 should be 30-1.5mm or close to 28.5mm. M31x1.5 should be 31-1.5mm or close to 29.5mm.

Those may fit

https://www.feked.com/ossa-bultaco-fork-stanchion-top-nuts-with-ball-valves-35mm-betor-forks.html