Author Topic: threads  (Read 1556 times)

Offline Ethelred

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threads
« on: 30.09. 2013 17:52 »
Recently I fitted a new clutch from SRM. The centre nut was incredibly tight. The old nut spun on and off with one finger whereas the new one was a pig. Eventually after cleaning everything, and to-and-froing with with some grinding paste I got it on tight. Took hours. Unfortunately I had no taps and dies of the right size.
I had to pull the primary apart again so I thought I'll fit an SRMs cush nut so as to set the 65 ft/lb torque properly. Exactly the same problem. Old nut can be spun on with one finger, new one goes on about three turns and seizes. I gave up in the end and put the old one back on and drifted it up tight.
It seems unlikely that a firm of SRM's reputation could be producing parts that fit so badly, so is this just down to BSA making the originals on clapped out machinery thus having more play? Anyone had any similar experiences?
'59 A10

Online bsa-bill

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Re: threads
« Reply #1 on: 30.09. 2013 18:13 »
I've had a variety of clutch centre nuts due to the fact there are quite a number of different ones for the two types of clutch used, never had a problem with threads on them though, having said that I've never had SRM supply any.
Is it Stainless by any chance, I once had a stainless rear axle nut from Molnar that was just to tight and they would not take it back, purchased another from elsewhere and it went straight on no problem (stainless MUST be lubed when fitting)
All the best - Bill
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1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online chaterlea25

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Re: threads
« Reply #2 on: 30.09. 2013 19:06 »
HI,
Its likely that the end of the crank is slightly damaged and the old nut worn so it fits ok
A trick if you have a spare old nut of the correct size is to cut an old nut almost in half
Screw it on most of the way, then squeez it with a vice grip or similar while you wind it back out over any damaged threads, carefully done it will clean up the damage  *idea*
The clutch centre nut is likely a "wassell" product???
I have had to run a tap through any of these I have fitted !! I suppose it would be worse if they were too loose????

HTH
John
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1963 RGS (ongoing)

Offline scotty

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Re: threads
« Reply #3 on: 01.10. 2013 01:05 »
Ethelred

I too have just this week fitted a new complete 4 spring SRM clutch.
The clutch center nut provided was a good fit.


I also fitted a SRM cush nut which was a bit tight going on and I've had it on and off a few times trying to get correct alignment with clutch and thread is still good.
I didn't have an old one to compare it  though  *conf*

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Offline wardleybob

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Re: threads
« Reply #4 on: 01.10. 2013 18:19 »
Hello I have had trouble with oil pressure relieve valves from srm they used to lend you a tap to tap your
Cases

Offline pjm01

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Re: threads
« Reply #5 on: 06.10. 2013 17:27 »
I've had a problem too with new clutch centre nuts not fitting (at all). With a great deal of forum help I got the old 6 spring clutch apart and ordered a '4 spring clutch conversion' from a respected supplier. All assembled well (with a little bit of fettling) apart from the clutch centre nut which would not even start on the shaft thread. They sent me another and that was just the same. Measurement of internal diameter of the 'old 6 spring nut' was 15mm and I/D of both new nuts is 14.5mm ..... just don't know what to do now as supplier said to return them for credit but could not offer a more 'creative' solution. If a new nut 'started' on the thread then I'd be happy to try running them forward/backward with a bit of grinding paste but I don't have that option. Any good ideas please (I'm a novice/newby and don't have taps/dies etc) .... guess I could get a new nut made up by a local engineering company if I knew details of the shaft size and thread details but that sounds an expensive option.
(Bike is a '59 A7 SS) ... Peter M

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Re: threads
« Reply #6 on: 07.10. 2013 12:25 »
G'day Peter.
The thread on the mainshaft is 5/8" x 20 tpi bscy (cycle) 60 degrees.
Cheers
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Offline pjm01

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Re: threads
« Reply #7 on: 07.10. 2013 15:06 »
Muskrat ..... that's brilliant ...... thank you so much, I can progress now. Peter M

Offline Ethelred

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Re: threads
« Reply #8 on: 07.10. 2013 16:48 »
Muskrat, do you happen to know the spec for the thread on the end of the crank that the cush nut screws onto?
'59 A10

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Re: threads
« Reply #9 on: 07.10. 2013 19:31 »
G'day red, it's 5.30am, I've got the BBQ going to drop a new roller conversion bearing into the cases. Will measure it up before I go to work at 7.
Back soon.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, .
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Re: threads
« Reply #10 on: 07.10. 2013 19:53 »
3/4" x 20 tpi bscy.
Cheers.
Hot cases for breakfast, burnt fingers for lunch  *doh*
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Online WozzA

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Re: threads
« Reply #11 on: 08.10. 2013 06:06 »
3/4" x 20 tpi bscy.
Cheers.
Hot cases for breakfast, burnt fingers for lunch  *doh*
*smile*  nothing wrong with Barbie BSA Bits 4 Breckie..   *clap*
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Re: threads
« Reply #12 on: 08.10. 2013 09:35 »
I bought a die for the cushdrive end of the crank as the shop had dulled it a tad and the SRM cush nut was not keen to start (so I have bought threads from SRM)

Worked great just used it by hand first then gradually closed the die a bit at a time by holding it in vise grips, really did little more than clean the threads up but made all the difference.
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online morris

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Re: threads
« Reply #13 on: 09.10. 2013 21:36 »
3/4" x 20 tpi bscy.
Cheers.
Hot cases for breakfast, burnt fingers for lunch  *doh*
*smile*  nothing wrong with Barbie BSA Bits 4 Breckie..   *clap*

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