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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Vincent Head Exhaust Threads
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<blockquote data-quote="Robert Watson" data-source="post: 128968" data-attributes="member: 38"><p>I have repaired exhaust port threads a couple of ways. </p><p></p><p>as above I made a tapered mandrel and pushed it through older nuts to tighten up the fits into the ports, these for ones that feel just a bit loose. </p><p></p><p>next - a local who shall remain unnamed, made a three part tap - the first part is a standard 1 7/8 X 20 TPI tap that is just a few threads long, you can screw this into the existing port, right to the bottom where it picks up well on what is usually the last few remaining good threads in the bottom of the port. It has a timed 20 TPI stem. Down this timed stem goes part number two which is a starting tap at .050 oversize and also timed 20 tpi inside and out. when it has done its job and is removed next goes down a finishing tap made the same way. finally the pilot is removed and the finishing tap taken right to the bottom of the port. Now you have a virtually brand new thread but + .050</p><p></p><p>here come the fun.</p><p></p><p>I have made new nuts from scratch that are .050 oversize as one solution for the nuts. </p><p>the other one is to make a straight stub that is .050 oversize. Having done this you can now take an old worn out nut and bore it to suit the stub with a couple of thou interference fit, I think I may have stepped the stub at the appropriate length as well, in any case this can then be pressed onto the stub and there you have a new nut, and a little easier that making a new one from scratch. I had worried a little that the flange part of the nut may come loose from the stub and was prepared to make a couple of little lock screws to hold it in place but in many years and many thousands of miles this has not been required.</p><p></p><p>this can quite easily be done on the bike with only removing the exhaust pipes.</p></blockquote><p></p>
[QUOTE="Robert Watson, post: 128968, member: 38"] I have repaired exhaust port threads a couple of ways. as above I made a tapered mandrel and pushed it through older nuts to tighten up the fits into the ports, these for ones that feel just a bit loose. next - a local who shall remain unnamed, made a three part tap - the first part is a standard 1 7/8 X 20 TPI tap that is just a few threads long, you can screw this into the existing port, right to the bottom where it picks up well on what is usually the last few remaining good threads in the bottom of the port. It has a timed 20 TPI stem. Down this timed stem goes part number two which is a starting tap at .050 oversize and also timed 20 tpi inside and out. when it has done its job and is removed next goes down a finishing tap made the same way. finally the pilot is removed and the finishing tap taken right to the bottom of the port. Now you have a virtually brand new thread but + .050 here come the fun. I have made new nuts from scratch that are .050 oversize as one solution for the nuts. the other one is to make a straight stub that is .050 oversize. Having done this you can now take an old worn out nut and bore it to suit the stub with a couple of thou interference fit, I think I may have stepped the stub at the appropriate length as well, in any case this can then be pressed onto the stub and there you have a new nut, and a little easier that making a new one from scratch. I had worried a little that the flange part of the nut may come loose from the stub and was prepared to make a couple of little lock screws to hold it in place but in many years and many thousands of miles this has not been required. this can quite easily be done on the bike with only removing the exhaust pipes. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Vincent Head Exhaust Threads
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