SRM clutch

[KeithJ]

I have found there is just enough space to fit 6 bonded plates plus one extra plain plate from a 7 plate conversion in the SRM clutch. These plates appear to have some bronze in the bonded material.

Photo shows Aerco plate compared with Surflex.

   I guess the Aerco plates are the next ones I should try.  Are they for wet or dry clutches?  Should I be able to just change over the friction plates instead of going for the full 7 plate option?
Thanks
 

[JulianS]

Wet. I always use SAE 20 oil, having got some slip with ATF 7 or 8 years back.

You should be able to put 6 straight in, though I did find that they were a quite tight on outside diameter in one chainwheel but OK in another.

The bonded material is obviously thinner than a standard plate.

I did not try 7 plates in a steel chainwheel because I was not convinced that the rivetted construction was suitable for it. hence the alloy chainwheel. I would not have considered using 7 plates without the SRM thrust washer. Removal of the lip (quite soft I filed it off) on the centre drum is to allow the first plate in (bonded) to seat square on the chainwheel inner surface.

I think there are several options/makers of the 7 plate clutch kits, which include an extra plain plate plate. Dont go for the early 4 spring A65 version which includes a plain plate with different shaped tongues which are not compatible with the A10 4 spring.

[Black Sheep]

I use tractor universal 10W-30. It's cheap (great!) but not only is it a diesel engine oil, it is also suitable for hydraulics and most importantly for tractor oil-immersed brakes. No anti-friction additives. Ideal for oily clutches.

[KeithJ]

Wet. I always use SAE 20 oil, having got some slip with ATF 7 or 8 years back.

  Isn't the BSA clutch a "dry" one?  Didn't think it was a wet clutch, it just happens to have oil around it?  It is essentially the same as the plunger one which had a cover on it and that was a dry clutch.  What type of ATF did you have problems with?  Was it Type F?  Thanks

[JulianS]

The 4 spring clutch is a Triumph design which was introduced in the 1930s.

Triumph workshop manuals over the years tell us that these are clutchs are designed to operate in oil.

Regret II dont recall which of the many formulas of ATF I used.

[RDfella]

Maybe the manual says the clutch can run in oil, but then the scribe didn't have to start / ride a bike with a slipping clutch. And why did BSA fit a dome over some of its clutches to keep the oil out? I disagree with the manual's advice and can say I 've always had trouble with slipping clutches  (BSA / Norton / Triumph) whenever I've had oil in the primary. Strangely, my Velocette never complained too much, but then the cases used to leak (and were such a bugger to put together) that there probably wasn't any oil in there anyway.

[KeithJ]

Had the same 4 spring Triumph type clutch in my A10 for forty or so years.  Never had slip problems.  Used ATF, but mainly 20W-50.  Fitted the "improved" SRM one and at the same time an electric starter about 5 years ago when completely rebuilt the bike.  Had issues since.  Bought some replacement friction plates must be thirty plus years ago and still have them.  May fit them to see if they are an improvement on the modern SRM ones.  Look the same to me though.  Interesting times working out what's likely to work and the best combination.  Sometimes wonder if better to leave it standard but should be able to improve on what was designed all those years ago surely?  Surely if the clutches were designed to run in oil, there would not be so much concern about the quantity of oil in the chain case?  It is said the oil is there to mainly to lubricate the chain.

 I've run Suzuki clutches on my Vincent when I had it.  Modified the clutch housing to allow oil to enter.  Used various oils with no slipping  problems.  Problem there was getting enough oil to it!  However, I think they are "wet clutches".  KBO!

[morris]

Ha! The ongoing clutch saga....
Here’s my experience; I used to run a straight hydraulic ISO 32 oil in the primary cases of both the plunger (6 spring) and the SA (4 spring). This oil came out best after experimenting with different oils.
The plunger clutch always ran fine, but the SA clutch kept having a tendency to stick, so I changed both to ATF fluid.
This made no change to the plunger clutch, but it made the SA clutch slip and made no change to the sticking.
I changed the SA back to hydraulic oil, this stopped the slipping but it’s still sticky. When I clean the plates it behaves flawless but after an hour drive it starts sticking again. When pulling the lever the clutch takes a couple of seconds to release, and if I select first gear too hasty it replies with a crunch. Careful setup and an SRM pressure plate improved matters but only up to a point.
Strange thing is that it’s only the outer plates that are oily and stick. Further up the basket the plates are bone dry and release straight away.
What puzzles me most is that I have the plunger clutch running without the clutch cover, so oil can get everywhere but it never sticks, while the SA has the (in)famous oil flinger which seems to do it’s job in keeping oil away (except from the first plates). I did an experiment with a chain wheel of which I removed the “flinger” but this only made things worse so back to square one.
Investigations ongoing....

[KeithJ]

Morris, very interesting.  Some thoughts, are the friction plates the same material? How do the spring pressures compare? How often and how many miles do the bikes cover in a year?  How are the bikes ridden?
I wonder if the harder they are worked, less the problem?

[orabanda]

Hi Morris,
What is the pivot centre distance of your clutch lever?

If it is 7/8", then the clutch operation will be approx 25% lighter than a 1 1/8" centre / centre lever, but the plate movement will be same amount less.

I have found some clutches need the 1 1/8" lever to fully disengage when cold.

Richard

[JulianS]

Plain plates are often not completely flat, even new ones.

[KeithJ]

If I recall correctly, Suzuki clutches can be fitted with plain plates which have lots of "dimples" or similar fine bumpy surface and used to improve the operation of the clutch. Perhaps thats why abrading plates makes ours work better until the abrading gets worn away?

[morris]

Hi Morris,
What is the pivot centre distance of your clutch lever?

Aha! Now there’s something! I just measured both levers and the SA has 7/8 while the plunger has a 1 1/4 pivot.
So many discussions about this issue, and it never occurred to me that this may explain my problem! 
Thanks for the tip Richard, I’ll swap the levers ASAP and see what comes out.
Regarding the plates, both came from the same supplier (which of course don’t mean that the friction material is the same as the plates are physically different and could come from a different source)

[RichardL]

Not reading the whole 9-page saga before posting in this topic.

I'm quite excited right now. SRM 4-spring clutch just arrived. It's going on the running A10 (not WHILE it's running) so that the 6-spring can go on the A7 in the works. One of my justifications is that the lower-powered A7 will do better with the 6-spring than the A10 does. New clutch may even be installed on the A10  in time for a weekend ride. Definitely before DGR.

Sooo pretty.

Richard L.

[BagONails]

Not reading the whole 9-page saga before posting in this topic.

I'm quite excited right now. SRM 4-spring clutch just arrived. It's going on the running A10 (not WHILE it's running) so that the 6-spring can go on the A7 in the works. One of my justifications is that the lower-powered A7 will do better with the 6-spring than the A10 does. New clutch may even be installed on the A10  in time for a weekend ride. Definitely before DGR.

Sooo pretty.

Richard L.

Hi Richard, I've been reading through this thread in preparation for fitting my new clutch parts (friction plates/plain plates/ billet pressure plate and release bearing etc.). I was wondering how you have got on with yours if indeed you've got around to fitting it yet  as I know you've been busy with your other build and the lathe etc.

I have found the revised SRM notes to still be a bit of a dogs breakfast to be honest they seem to have some of the operations out of sequence still but I've got everything fitted now.  (Thanks to Roger too for his notes, most helpful and confirmed my own thoughts.) After removing the chainwheel I found my previously fitted new adapter is not compatible with the SRM thrust bearing and would need to be removed and have a relief ground into it to replicate the SRM one. I decided this probably wasn't worth it so have left the thrust washer out. (I didn't buy a complete SRM clutch as I'd already changed a number of items previously)

Unfortunately at some stage in my deliberations my clutch cable outer must have moved and fell out of one of the ferrules which meant my measurements for cutting the push rod down were wrong! I might try the old cut in half and fit a steel ball in the middle trick as this will make up the difference, failing that I'll get another length of silver steel and start again! Certainly in no hurry to get the primary case back on at this stage...

Oh and as this topic included some discussion about oil levels I thought I'd have another look at that too.
The second photo shows my spirit level sitting, well level, as it were (yes I know in the picture it looks anything but but it was level honest, check the bubble!) and just nestling up underneath the chain wheel so that if the top surface represents the oil level in the case then the chain under the chain wheel would be totally immersed in the oil when stationary on the centrestand. My workshop floor is level but the bike sits up with its rear tire 3/4" (look at me, inches even  ) off the deck so when on its wheels the chain would be probably at least 1/4" deeper in the oil.  The level is sitting about 1/4" above the bottom face of that little impression in the rear cover that I assume is to assist taking the split link on and off although you don't actually need it.  Handy though as you can see this feature with a pencil torch through the filler hole and thus you can visually see your oil level. I've now physically scratched a reference line here that I can use as my guide which will take all the mystery out of things..shame shame....