Clutch and changing down

[Ray Martin]

Hello folks,

One bit of info and one question.....

INFO - I've been having some trouble changing down gears. It's not that the clutch doesn't disengage, it's the opposite. It disengages so well that revving the engine, I have to pull the lever in only 7/8 of an inch to get it to the point where disengagement has taken place but there is enough friction to help spin up the mainshaft. I did a longish trip on Friday with lots of windy roads and gear changes and there was a lot of grinding and gnashing of teeth. The box seems very unforgiving if I don't get it right.
So this weekend I stripped the clutch, took the Surflex plates out, and put back some old cork ones.
The result is much easier, I now have much more of a lever distance where there is some drag.


QUESTION - Whilst changing the plates over, I looked at the parts book and engine manual. Both say there should be 5 plain plates and 5 friction plates. Thick plain plate in first and using the pressure plate as the final driven plate. In mine, there were 4 friction plates and an extra plain plate in front of the pressure plate - the clutch never splips but it has one less friction plate than standard. I tried fitting back one of the Surflex plates but adding that thickness to the stack seemed to put the pressure plate at a position where it was very close to becoming disengaged from the splines. I chicken out and went with 4 friction plates. Should I have gone for 5?

[Triton Thrasher]

I don’t know what kind of clutch you have, but if it doesn’t drag or slip, just be thankful.

I also have found that cork works better as a friction material in a wet(ish) clutch than Surflex’s patent compound.

[RDfella]

I tried fitting back one of the Surflex plates but adding that thickness to the stack seemed to put the pressure plate at a position where it was very close to becoming disengaged from the splines. I chicken out and went with 4 friction plates. Should I have gone for 5?

There are different depths of the inner (and outer) clutch 'baskets' depending on model. The singles - eg B31 - only had about 3 or 4 plates, the Gold Stars more. The more bhp, the more plates BSA fitted. Now, after 60 yrs, how often has that clutch been visited, and were the correct parts fitted?  I agree with TT - cork copes better with oil: indeed it is required to stop the plates burning. That's half our problem these days, putting plates that need to be dry (would you put oil on your brake shoes?) into an oily environment and expecting them to work without slipping or sticking. Remember, back in the days our bikes were made, cork was the material used.

[Swarfcut]

  Ray, your third sentence is a bit of a conundrum. If it said  " I only have to pull the lever 1/8" for it to disengage" it would make sense, 7/8" should not be necessary to free the clutch from driving, but to ensure the plates are free to float. This may be the problem, in that the plates are not free to move in their locations and even when the clutch lever is fully back the mainshaft is still being driven and the gears crunch, the symptoms of clutch drag.

  I'd suggest a look at the  tangs on the plates the ease of movement of the lined driving plates in the basket and the condition of the clutch centre and plain driven plates. All suffer from burring to some degree, and if the plates can't move apart the clutch will drag.

 Your earlier posts concern the A7 Longstroke, the above points apply to all clutches. The later 6 Spring pressed steel centre  S/A clutch is a different design, alluded to by RD.

 As RD indicates, for this clutch type over time a mix of parts that work but which are not strictly correct for the model may be found, and that goes for the clutch lever as well...there are different lengths of clutch lever pivot/nipple distance, so varying throw.
 For the 6 Spring S/A Clutch the number of plates used is more often a function of the depth of the clutch centre...... there are 3 size variants that I know of.  The chainwheel  found will generally be the right one, but you can never be sure.

 There should always be a tiny bit of slack in the cable when the clutch is fully engaged, and the position of the operating lever on the gearbox clutch arm can also be altered, (usually by folks who should know when not to mess) in an attempt to get more lift. Plenty about clutches and their finer detail available on the Forum.  The clutch springs need to be adjusted so that the pressure plate lifts squarely ie. does not tilt.

 Swarfy.

[Ray Martin]

Thanks for your responses guys.
I should have clarified, Swarfy, that it is a dry clutch - I had assumed probably incorrectly that all A7 clutches in 1946 to 1950 were the same.
It has a sealing dome and (whilst the primary has plenty of oil) the dome and rubber seal, do a perfect job - the clutch stays bone dry and I don't get greabox oil down the shaft.
The clutch centre and basket are in good condition: no ridges and the plates all slide in fine, with small clearances.
With the Surflex plates fitted, it goes into first easily at a standstill and never crunches - that's the upside.
The downside is, when changing down gear, and a constant mesh box. You rev the engine with clutch pulled in so as to apply a speeding up force to the main shaft so that when changing gear, the shaft spins faster in the fraction of a second it is between gears and thus moves without a crunch. I have a feeling I have an box with very little backlash in the bits that provide the coupling and thus, this needs to be got right to get the gear change. When using Surflex plates, the positioning of the handlebar lever to get the drive to break but enough drag to allow the speeding up process is very hard to accurately find - if I get it right, it's fine (no crunch) but it's very hard when doing a lot of gear changes on unknown tracks.
Having now replaced it with older cork plates, it seems much easier. I took it around the block (large block) yesterday evening and tried the handlebar lever in several positions when changing down and all seemed well.

Thanks RD for the info about different sizes of basket, that could well be the case. I think I changed the clutch basket and centre for some I found at an auto jumble, but that was back around 1981. I don't remember changing the number of friction plates though. It doesn't slip with 4 friction plates so I will happily stick with that.

I would like to get a new set of corked plates - the ones I have in there are quite worn hence the purchase of Surflex replacements. Does anyone on here know if I can get the ones I have recorked or even if I can buy clutch corks?
Also, does anyone have a set of old cork plates they would be willing to sell?

[Triton Thrasher]

I picked the Surflex material off the plates and used impact adhesive to stick whole circles of cork mat in its place.

[RichardL]

I picked the Surflex material off the plates and used impact adhesive to stick whole circles of cork mat in its place.

Love these kind of outside-the-box mods. Can you explain what you mean by "impact adhesive."
 Not a term used over here.

Richard L.

[Triton Thrasher]

Commonest kind in U.K. is Evo Stik.  It’s yellowish and stringy and messy, with a strong solvent smell.  You apply it to both surfaces, let it dry, then press the things together.

It was used a lot for sticking laminate surfaces to boards, back when kitchen worktops were made like that.

[Ray Martin]

TT, what cork mat did you use? I measured the thickness of a corked plate (somewhere around 3.5mm in total) so that must make the width of the cork bit on each side around 0.5mm.

[Triton Thrasher]

I used thin cork gasket material.  Can’t tell you the thickness.

Then I ran out of that stuff and got cork mat for “craft” people from EBay.  I still have some left and I’d measure it if I could find it!  Probably 1 mm.

They can be sanded down if too thick.  I think someone on here said they thin and smooth the lining on a lathe, too.

[RichardL]

As soon as I read the description of "Impact," I realized it must be the same as the product known here as "Pliobond," which I first knew of in the late '60s or early '70s while working in the loudspeaker manufacturing business. A little research showed what I thought must be true, both manufactured by companies under the same parent, Bostik. Yes, I breathed in a lot of that solvent, and the odor was very distinctive.

Of course, they may be somewhat different, but sure seems like they're, at least, related.

Richard L.