Hi,I'm restoring my 1955 BSA B31 after using it for 15 years.On opening up the clutch I found that I'd been running the bike on a M20 cluch.There has been no issues with the clutch and I would like to continue using the bike with the same clutch assembly but the inside of the alloy clutch case has been scored by contact of the bowler hat type clutch cover,so it isn't such a good idea to continue with it's use.I wonder if there is a fix for this. In case there isn't one,does anyone have a six spring (which I hear is pretty crappy) or four spring complete cluch assembly that they would like to flog?

Any pointers or ideas would definitely be appreciated.
Cheers,
Hank

Hi Hank..Are you sure the clutch bowl is contacting the cover and the marks inside the outer cover are not just the result of a clutch coming loose in the past?
One thing to check is that the inner clutch case is mounted correctly. When the cover is bolted to the crankcase there is a gap behind the lug at the clutch end of the cover where it bolts to the frame. There should be a spacer there...If that has been left out the cover will be pulled closer to the frame (and clutch).
Other than checking that there is not much you can do as everything is in a fixed position, though if there is room behind the clutch it might be possible to space the inner case a little further off the crankcase. You would then have to alter that spacer and you would need to consider footrest clearance etc.
My opinion of the 6 spring clutch has been expressed previously (though there are those who don't agree) and I wouldn't even consider fitting one. If you do need to change the clutch I would go for the Triumph 4 spring unit fitted with the lighter of the two available 'weights' of pressure springs....Ian

email (option): ian@wright52.plus.com

SRM offer a Triumph 4 spring clutch kit (LINK) it comes with everything pictured, i bought one which is compatible with the plunger/rigid gearbox on my '52 B33 as the original 6 spring clutch on the bike was completely thrashed, the finish on this bit of kit is quite impressive, it's easily the tightest bit of engineering on the whole bike though i shouldn't say to much because i haven't actually finished the rebuild and run it yet!

I have a friend who raced Goldstars in the mid 50's, he used one bike to race road, scrambles and trials events all with a 6 spring clutch, he told me recently he never had a problem with the design, they just needed to be set up correctly and kept adjusted, for him this clearly was not an issue though I can understand others who opt for a slightly more robust design with hopefully less maintenance, each to their own.

Hi Ian W, Ian C and Nick, thank you for your suggestions and sorry for a tardy reply-I'm away at work and just found the time to reply. I think Ian W has a point as I did not find any metal filings on the inside of the clutch case when I got it opened, so I think I will fit the M20 clutch assembly back and ride the bike with it until I find another clutch for it.
I spoke to a guy at SRM and was told that it would take around 3 weeks to a month to get a clutch assembly organized-so that definitely is an option.
In the meanwhile the bike has been stripped and parts separated into piles for chrome and paint.I'm having the crank reconditioned.
I will pick up where I left off, in four weeks from now.I will also try keep you guys updated and hopefully things will go smoothly-as I plan to have the bike up and running in seven weeks.

Hank... Thanks for mentioning the single spring clutch fitted to your B31. I went ahead and fitted the same clutch to my 1953 metal chaincase B33 over the weekend and after a good ride out yesterday I found it works extremely well! To my suprise it worked with the full set of plates (eight of) the lever is still a little stiff but much better than what my six springer was, there is no drag or slip. I'm wondering now if I could get away with removing just one plate, is this asking too much from a B33 I wonder? The only other problem I found was the 6 millimeter stainless steel push rod is no good, I'm amazed how quick that started to wear to concaveature. (is that a word?) a proper 1/4" mild steel one has been oredered.

P.S I also found the bowler hat cover just touches the outer metal chaincase cover but only by a couple of millimeters, a big hammer will sort it.

Hi LJ..If you remove plates from the M20 type clutch you need to remove the last two..one steel and one fibre, so that you still 'finish' on the same type of plate. That gives more room for the plates to seperate and should work without problems on your B33.
Having a shallower 'stack' of plates may lead to you having to make a slight alteration to the pushrod length.
The pushrod you are buying should be made from 'silver steel' and have the ends hardened. Silver Steel is a flame hardening high carbon steel and it is easy to make alterations to a pushrod made of this material if required.
First you will need to soften one end.
Heat the end to red and allow it to cool naturally in the air. This will soften or 'normalise' it.
Once cold shorten the rod to the desired length..but take care. Small reductions in length make a lot of difference. When you are happy the rod is correct and the clutch adjustment is correct with the rod fitted, remove it and heat the end you have altered to red, quenching it immediately in cold water.
This will re harden the end.
Then clean the end off with some emery cloth until you have a bright finish.
You will now have to 'temper' the end. (this softens it slightly and makes it less brittle.)
Place the end into a fairly gentle flame and allow it to slowly heat up. You will see the steel gradually change colour as it heats, first to a very pale yellow, then a darker yellow...then brown. This is an indicator of the changing temperature of the steel.
Allow it to go pale yellow and just as it starts to darken quench it very quickly in cold water. The rod is then ready to use.
If you go too far and the rod goes brown simply heat it to red, quench it again, clean it off and have another go. Lubricate the rod well with some light oil before refitting...Your stainless rod was not a suitable choice...the material is far too soft and that is why it didn't last long!....Ian

email (option): ian@wright52.plus.com

Thanks Ian... I removed the two plates today (one fibre and one steel) Easy job with correct tool. The result is that I now have a silky smooth clutch and light as a feather! The B33 copes very well with it. Its interesting that you 'know' you have a single spring clutch operating as it is nothing like the multi spring clutches. Just got to seal up the primary case now and hopefully that'll not want attention for many years to come. here's hoping!

Hi LJ..Yes, I found the same thing..the 'feel' is quite different. Hard to work out exactly what that difference is though!..Glad you got it sorted anyway...Ian

email (option): ian@wright52.plus.com