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A50 Clutch release plunger #744987
08/09/18 3:13 pm
08/09/18 3:13 pm
Joined: Sep 2014
Posts: 208
Ohio
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Andrew Dunham Offline OP
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Ohio
HI everyone,

Hopefully simple question here. Trying to troubleshoot a clutch problem on my 68' A50.

I discovered that the ball bearing has basically pressed itself INTO the release plunger. I cannot remove it. The parts book lists these are separate items, so surely this can't be correct?

The clutch would work when the bike was cold and then get substantially more difficult as it warmed. I believe this is due to the push rod not fully disengaging the plates because the ball has embedded itself into the plunger.


Does that make any sense?
[Linked Image]

Last edited by Andrew Dunham; 08/09/18 3:18 pm.

1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
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Re: A50 Clutch release plunger [Re: Andrew Dunham] #744988
08/09/18 4:03 pm
08/09/18 4:03 pm
Joined: Aug 2001
Posts: 4,106
argyll. scotland, uk
gavin eisler Online content
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gavin eisler  Online Content
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argyll. scotland, uk
Yup, should be a smaller ball. good luck getting it out, if you want to save the plunger maybe drill a wee hole through from the opposite end and try to knock it out? A 3/16" diam ball should work.
or leave as is, cut the push rod in half , fit a ball between the two halves,
this is quite a common mod,
two short rods are stiffer than one long one., one of the new shorter rods will need to be shortened to allow for the new ball, after you sort out the correct lengths ( do test this, once cut theres no going back) ., harden the ends of the cut rods when happy with operation , heat to cherry red at the end , not the whole rod , then quench in oil.
The jammed in ball will be redundant, the new ball should deal with the spinny bit.

Last edited by gavin eisler; 08/09/18 4:10 pm.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: A50 Clutch release plunger [Re: Andrew Dunham] #744992
08/09/18 4:09 pm
08/09/18 4:09 pm
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Ohio
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Andrew Dunham Offline OP
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Thanks, Gavin.

So 3/16" is the required size ball then?

I will most likely replace the plunger as I noticed some chips removed from the LH side of it in the picture.


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: A50 Clutch release plunger [Re: Andrew Dunham] #744993
08/09/18 4:17 pm
08/09/18 4:17 pm
Joined: Aug 2001
Posts: 4,106
argyll. scotland, uk
gavin eisler Online content
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gavin eisler  Online Content
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It is IIRC, last time I did this I just found one that fitted OK in a drawer full of push bike stuff.
Push rod length.
Something to be aware of, with a new plate stack , ie max plate depth, the centre adjuster screw should be just flush with the lock nut on the pressure plate, as the stack wears down , the push rod should stay the same length , , this allows max adjustment to give correct push rod endplay, as the stack wears out the screw is screwed out to set end play.

IIf you do it the other way round and cut the rod long so the screw is protruding with a new plate stack, the screw end will foul the inspection cap when the clutch is disengaged and the pressure plate moves outward, theres not a lot of room here.
One of the many mistakes I have made.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745000
08/09/18 5:03 pm
08/09/18 5:03 pm
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Posts: 208
Ohio
A
Andrew Dunham Offline OP
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Ohio
From what I can tell, vendors are listing the ball bearing as 7/32". My local hardware store doesn't stock those, but does stock 3/16" so I'll order a 7/32" and stop over there and pick up a 3/16". Easy.

Interesting about the screw. Mine was hardly turned in before it bottomed against the push rod...

I thought I had it figured out with the ball and plunger, but now I've got something else to look at!


I've somehow got three push rods sitting around, so I will measure them and see if the currently one is too long.


Seems like I've got a bit of operator error and lack of research going on here.


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745041
08/09/18 10:57 pm
08/09/18 10:57 pm
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DMadigan Offline
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VXB.com has loose chrome steel 7/32" balls ($0.77 each G10, $4.95 for 100 G25). McMaster.com has them also.

Re: A50 Clutch release plunger [Re: Andrew Dunham] #745044
08/09/18 11:34 pm
08/09/18 11:34 pm
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argyll. scotland, uk
gavin eisler Online content
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If the plate stack is not brand spanking new ,steels as well, fresh, maybe allow a little extra on the screw in case you ever feel the need to put a whole new stack in, some new plates are thicker than others.

If the stack is worn enough to fit another plain steel plus 1mm of cork you can win extra area for pretty cheap, empty the basket, clean the back of the drum , use carpet glue to stick 1mm cork sheet to the drum inner face. Cork must be trimmed neatly to fit, first , scissors and compasses, cut the holes out later after its been glued down, .
Now the first plate in is an extra plain steel which will now drive with the cork, after that it goes friction / steel as normal.
You get 3 more driven surfaces, because the normal set up with first plate in as friction doesnt use the inner side. Works out at about 20% more area. The rod might need to be a bit longer if you do this.As long as the plates stay in the notches when pushed out all will be well.
Also the drum notches must be smoothed out or the displaced plates will be caught between grooves.

If you do this you can back off the spring pressure a bit for a lighter clutch.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745048
08/09/18 11:47 pm
08/09/18 11:47 pm
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DMadigan Offline
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But, of course, friction force is independent of area: F = mu * N

Re: A50 Clutch release plunger [Re: Andrew Dunham] #745059
08/10/18 2:54 am
08/10/18 2:54 am
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Ohio
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Andrew Dunham Offline OP
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Gee Gavin, you sure do know a lot about the subject! What's shipping from the US to Scotland these days?!

I actually have two complete sets of barely worn plates (shamefully.) I threw money at the problem until I realized it wasn't going to fix it. I measured my new basket and the original and the basket depth was the same. I was concerned that since I ordered the new basket for a 7 plate conversion, it would be deeper. 36mm or so. I think I can simply interchange a 6 plate setup if I want to.

I'm going to measure both sets of plates and see if they're within spec and flat. If so, I'll come up with a solution for either 6 or 7 plate. I do think my next hurdle is the push rod and making sure I have it the right length.

I'm intrigued by the SRM (or MAP cycle) alloy pressure plate and plates, but cutting the push rod short and re-hardening will take some research and bravery since I've never done any hardening before.


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745091
08/10/18 9:29 am
08/10/18 9:29 am
Joined: Aug 2001
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argyll. scotland, uk
gavin eisler Online content
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"But, of course, friction force is independent of area: F = mu * N"

its a long time since my schooldays with Mr Robertson at the the Academy, refresh me on mu ( coefficient of friction?) and N ( number of something?)

does this make multi plate clutches obsolete? Are you saying that adding extra plate area to the clutch is a waste of time?

If you have a MAP gas torch, colour vision, some old oil , gloves and pliers , heating / quenching is not that tricky, its quick and a bit dirty, fun with heat..


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: A50 Clutch release plunger [Re: DMadigan] #745105
08/10/18 11:42 am
08/10/18 11:42 am
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scotland
triton thrasher Online content
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Originally Posted by DMadigan
But, of course, friction force is independent of area: F = mu * N


Not independent of number of plates, because an extra pair of plates in line is an extra clutch, not just more contact area.


Amateur Loctite enthusiast.
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745114
08/10/18 12:59 pm
08/10/18 12:59 pm
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John Healy Offline
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The factors are coefficient of friction of the clutch facing material, number of friction surfaces, force applied by springs, and the mean effective radius of the friction area.
Actual contact area of the friction material is not a factor.

There is no such thing as a 7 plate conversion clutch basket. They gain the space for the extra plate by thinning the individual plates.

Hardening oil hardening drill rod (aka as a clutch rod).
http://threeplanes.net/toolsteel.html


Re: A50 Clutch release plunger [Re: Andrew Dunham] #745116
08/10/18 1:37 pm
08/10/18 1:37 pm
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BSA_WM20 Offline
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And if you are going down the two short rod route. use an old clutch roller rather than a ball.

IF you do not harden the end of the shortened rod enough they will mushroom on the ball bearing and become not particularly good rivets and a real !!!! to remove.


Bike Beesa
Trevor
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745118
08/10/18 1:44 pm
08/10/18 1:44 pm
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Ohio
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Andrew Dunham Offline OP
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Thanks everyone.

Good tip on using a clutch roller, WM20. I've got a few of those sitting around. I've also got a couple of old push rods as well, so I'll use those to experiment on.

That's about what I figured on the basket, John. I measured all of those plates at the minimum thickness and the total basket was only .004" thicker than 6 standard plates.

I've got 45mm springs in there now. Someone mentioned using Triumph 750 springs in an older clutch thread. Any idea why? Looks like they're also 45mm but it doesn't say anything about their spring force.


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745122
08/10/18 3:21 pm
08/10/18 3:21 pm
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Rotherham - S. Yorkshire
Allan Gill Offline

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I tried T140 springs with the 7 plate clutch, LP williams actually phoned me up to ask if I was sure, I went with it and could barely lift the clutch, changed to T120 springs and the clutch worked a treat. There are some terrible springs out there and possibly someone has been fobbing off low quality/spring strength springs as T140 clutch springs..... Maybe...


beerchug
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745135
08/10/18 4:35 pm
08/10/18 4:35 pm
Joined: Aug 2001
Posts: 4,106
argyll. scotland, uk
gavin eisler Online content
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if you do the 7 plate conversion then 650 springs are perfect.

750 springs are heavier, not needed. i used them for years with the stock clutch, was glad to see the back of them when I added another plate.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745142
08/10/18 5:45 pm
08/10/18 5:45 pm
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DMadigan Offline
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There is a seven plate "conversion" by replacing the entire clutch:
[Linked Image]
KTM plates. Not quite ready as I have to change over to the latest Belleville spring pressure plate.
An A65 version will be available also.

Re: A50 Clutch release plunger [Re: gavin eisler] #745153
08/10/18 7:01 pm
08/10/18 7:01 pm
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Ohio
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Andrew Dunham Offline OP
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Sounds like I can rule out the T140 springs. Thanks guys.

Gavin,

Do you know if the springs labeled for Triumph are any different than the ones labeled as BSA? Seems like the ones I've seen (and currently have) are labeled as both.

DMadigan, that's quite the set up! Looks great. I'm going to see how good I can get it without spending any more significant money. I'm ashamed to admit how much I've got into this ordeal.


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745161
08/10/18 9:25 pm
08/10/18 9:25 pm
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argyll. scotland, uk
gavin eisler Online content
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I got my 650 springs from Grins triumph, and the 7 plate stuff, when I compared them with the 750 springs fitted , the 650 springs were longer and were finer wire, by my crude scales tests they were s good bit lighter.
i put all the figures in another thread, let me find them.

Last edited by gavin eisler; 08/10/18 9:32 pm. Reason: had numbers of turns wrong.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745163
08/10/18 9:30 pm
08/10/18 9:30 pm
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Posts: 4,106
argyll. scotland, uk
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here it is.
Snipped from elsewhere.
Got the 650 type, picked the 3 most similar length, wire diameter 0.090" , approx 1.830 " long, 8 working turns, OD 0.655" , ID 0.450"

750 springs fitted previously were 0.110" wire diameter, 1.700 " long , 8 working turns. OD 0.658", ID 0.431"

Got the scales out and crudely measured poundage for a measured deflection with a large 31 mm plastic bush, spring in middle then pressed down on a sauce pan till the bush was trapped , very crude, measured spring deflection and noted scales, these are probably less than accurate by + or minus a good bit.
650 spring rate ~ 100 lbs/ inch, 750 spring rate ~ 150 lbs/inch probably a bit out on this I was pushing 5 stones to deflect about a 1/2" and refinement was tricky, I did repeat each a few times and the result are a best guess average.
The 70 manual says 113 lbs/inch with 9 working turns.

Most noticeable apart from length is the spring nut fit, loosy goosy on the 650 spring, quite tight on the 750 . looser by about 20 thou.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745248
08/12/18 12:34 am
08/12/18 12:34 am
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Ohio
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Andrew Dunham Offline OP
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I would love to get some spring measurements on what I have in there, but I'll have to come up with a solution similar to yours first.

Update:

I put in a good 6 plate system (almost no use, flat steel plates and good measuring friction plates), found my best pushrod of the correct length, installed the new plunger and ball, and got a proper length cable. The previous one was too short so the routing was compromising the feel, I think. I also used a dial indicator and got the pressure plate runout to about .016". I couldn't find a spec, but figuring that is around 1/64" it should be good.

So far the feel is much improved. I haven't ridden the bike yet, so I'm not sure if the clutch will slip, drag, or anything. I will do the oh-so-familiar process of re-assembling the cases, foot pegs, shifter, and kick start tomorrow morning and we will really see how it goes.

I'm going to pay close attention to the pressure plate center screw to make sure it isn't hitting the outer inspection plug.


I will post another update then. Thanks everyone for all the help and especially Gavin for the specs and information.

Last edited by Andrew Dunham; 08/12/18 12:38 am.

1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt
Re: A50 Clutch release plunger [Re: Andrew Dunham] #745255
08/12/18 1:46 am
08/12/18 1:46 am
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bodine031 Offline
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Before u button it up drop it into gear and rock it as you squeeze the lever and see how the release is/where it unhooks.
My A-65 has been using reg. HD Big Twin primary oil for many years. many also use for older Fords ATF
keep us posted

Re: A50 Clutch release plunger [Re: Andrew Dunham] #745341
08/13/18 2:23 am
08/13/18 2:23 am
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Ohio
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Andrew Dunham Offline OP
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Ohio
Well, SUCCESS (for now) I'm a pessimistic person, so it's nice to be surprised when it keeps working.

The clutch feel is much improved and there was no slipping or dragging.

I'll give it a few rides and see how it goes, but I'm optimistic.


1961 BSA Super Rocket
1968 BSA A50
1969 BSA 441 VS
1970 BSA Thunderbolt

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