paulmac Report post Posted April 24 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 Quote Share this post Link to post Share on other sites
johnmartin247 Report post Posted April 24 Diameter is 35mm but not sure of the pitch of the thread. 1 Quote Share this post Link to post Share on other sites
carl ekblom Report post Posted April 24 My nut measures 30.8mm so it ought to be M31x1,5. Quite unusual. 1 Quote Share this post Link to post Share on other sites
johnjsy Report post Posted April 24 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 ...... 1 Quote Share this post Link to post Share on other sites
feetupfun Report post Posted April 24 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 1 Quote Share this post Link to post Share on other sites
paulmac Report post Posted April 24 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 1 1 Quote Share this post Link to post Share on other sites
carl ekblom Report post Posted April 25 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 1 Quote Share this post Link to post Share on other sites
