SRM clutch

[RogerSB]

If it's any help?
I made it for my bike - 1960 GF.
I hope there isn't any mistakes in it.

[RichardL]

That's a useful list. I've saved it for reference. Don't know why I never bothered making my own (list, that is).

Richard L.

[Colsbeeza]

Thanks Roger,
I will be putting my chaincase back on in a day or so, and I know the screws aren't quite right.
Colin

[Colsbeeza]

I still haven't got my clutch Outer Cover back on yet. My Chaincase Screws seem to be all over the place in length. Goodness knows where they came from umpteen years ago.
I decided to measure up everything from first principles, and came up with the following stuff.
Colins Screw Lengths - Measurements of what I have, including a new set of SS screws I purchased many years ago, and which have not been cut to length except for the three large screws.
BSA A10 SA Chaincase Screw Lengths Sketch - I measured the depths of the Outer Chaincase holes from the base of the Fillister screws down to the gasket surface (You may find this fairly useful). Then measured the depths of the threaded holes in the Inner Case. All holes except one had no bottom (No. 7 on the sketch), ie the threads carried through to the other side. The depth of the inner case was 22.9mm average. I did not bother to detail the three large holes, as they go through into the crankcase. I will just use the 5/16" x 2" screws provided. Muskrat - do you know how deep the crankcase thread is before the bolt hits the flywheel.?? ie the actual depth of the thread in the bare crankcase?
BSA A10 SA Chaincase Screw Summary - I have detailed on this sketch the maximum length of the screws (below the Head) before they bind in the bottom of the threaded hole, or otherwise stick out the back of the inner chaincase. Then rounded off these measurements to give a practical length of the screws, ignoring the thickness of the gasket.
Surprisingly, it was very similar to Rogers List, except that I could get away with a bit longer lengths on some of them.
Before I get cutting the new screws to length , I might wait for you all to jump on me ( ie. provide some feedback).
Cheers Colin

[Colsbeeza]

OOps,
Here is a sketch with the depths of the chaincase holes as mentioned. Just realised that the other sketch does not have these measurements.
BSA A10 SA Chaincase Screw Hole Depths - This is the depth of metal from Under the Fillister Head screws down to the gasket surface of the chaincase. Might be worth mentioning that to get this measurement, I placed the cover face-down on a flat surface (table), and used a 20mm length of brass tube to seat on the screw head bearing surface - long enough to stick the thin bit of the Vernier calipers down through this onto the flat surface (table), and the blunt bit on the top edge of the brass tube. Then subtracted the 20mm from the measurement.
I can imagine that not everybody's chaincase holes would have exactly the same depth. There is considerable scuffing of the screw head bearing surface, perhaps significant loss of metal from new.
Colin

[RogerSB]

Excellent Colin  .
Here's a diagram I made for myself when I changed all my screws so I didn't get myself in a muddle (as I often do  ).
In your chaincase diagram, screw no 7 bottoming out at 43mm. Would that be because it's coming up against the front section of a fully enclosed chaincase?
Mine is just a chainguard, so no front section to butt up against the back of the inner primary chaincase at that point.

[duTch]

 

....I placed the cover face-down on a flat surface (table), and used a 20mm length of brass tube to seat on the screw head bearing surface - long enough to stick the thin bit of the Vernier calipers down through this onto the flat surface (table), and the blunt bit on the top edge of the brass tube. Then subtracted the 20mm from the measurement.....

 A variation f that can be to stick a 3/8, 10mm (I think it may really be ~25/64") drill shank in the head hole and measure from the mating surface to the drill- saves all the maths (every one of them)
 Also worth not having them protrude out the back of the inner case to gather dirt and crap to grind the threads on the way back out

[Colsbeeza]

Roger,
  I checked and the No.7 is a blind hole - or at least it was supposed to be. Some PO has tried to put in a full 1-3/4" screw and it pushed through a bit. See the photo Screw 7 Blind From Right Side. And a few more attachments:-
  A photo of the screws (Cols Chaincase Screws After Cutting) after cutting two of the 1-3/4" back to 1-5/8" to suit your Medium application.
 Then a photo of the finished screws laid out around the chaincase (Cols Final Screw Locations)
 Finally, a pdf of the layout (Chaincase Screw Layout). In this pdf, you will notice that the actual screw lengths are a little less than the nominal length - eg. the large 2" screws are actually 48mm - not much but worth knowing if you have stripped a thread - perhaps a slightly longer screw will get you out of trouble. (But keeping Dutch's comment in mind).
 A tedious exercise I hear you say? - but in a few years when dementia has set in it may be useful. Then again if dementia sets in I may not remember where to find this stuff.
Anyway, she is all back together now, so off for a ride as soon as the wind drops - it is howling here.! No not that sort.!
Colin

[Sav]

My four spring clutch dragge with thicker oil, straight 40 after a case of need, cleaned the plates and refilled with straight 20 and OK now.

[RogerSB]

Sav, this what I now use for my SRM 4-spring:-
https://www.ebay.co.uk/itm/5L-SAE-20-Monograde-Engine-Oil-SAE20-Classic-Motor-Oil-5-Litres-SAE-20W-/112556936365?hash=item1a34ea8cad

More info here:-
https://www.a7a10.net/forum/index.php?topic=13195.0

(Edit): Read Replies 3 and 6.

[BrianS]

I hope it's OK to tag onto this thread rather than start a new one.

I fitted an SRM clutch back along and it transformed my A10 – I am very pleased with it - particularly as it allowed me to find neutral when stationery

However, I am now experiencing slight clutch slip when opening the bike up and probably need to tighten up the springs now the plates have bedded in.

I found the SRM instructions saying that the springs should show approx. one coil over the spring cups as mine do. (Photos attached).

My question is how much of a turn or how many turns I can safely tighten the springs to stop the slip?

Many thanks

Brian

[muskrat]

G'day Brian.
That looks more like 1 1/2 coils. I'd set it to arrow in pic.
Cheers

[RogerSB]

Hi Brian,
This is how mine are adjusted. Posted these photos on here:-
https://www.a7a10.net/forum/index.php?topic=13049.msg104031#msg104031
but I've attached them again here. I get no slip or drag, light finger pressure at lever and slips easily into neutral at stop.
However, Gary from SRM commented on the spring adjustment and oil here: https://www.a7a10.net/forum/index.php?topic=13099.msg104714#msg104714

(Hope the links work ok).

[morris]

Agree with Musky. It needs at least one maybe even two turns extra.
Clutch slip is unnecessary loss of power and only slows you down... 

[BrianS]

Thanks guys! I also covered my back by emailing SRM and was surprised to get a very quick response from Gary - great customer service eh?

Anyways up, taking all the advice together, I have adjusted the springs to where Muskrat recommended and it took two turns.

I realise now that I hadn't screwed them in far enough on installation but my excuse is there was no picture on the SRM instruction sheet just the advice to leave a coil showing. My interpretation of that seems to have been wrong 

Just got to get it all back together again now. Broke the gasket getting the cover off but fortunately have a spare. Cleaning all the old gasket goo off the cover was fun - not.....

Brian