Transmission slipping at high revs and have no idea why

[Triton Thrasher]

Did you say there is pushrod free play?

If the stack of plates isn't thick enough, the pressure plate can hit the clutch centre before the plates are fully compressed. At least the later 4 and 3 spring clutches can do that and the plunger 6 spring looks like it could.

[owain]

Ah good point Triton Thrasher. Yep, there is free play with the pushrod. I've played around with it quite bit but it doesn't solve anything unfortunately. I'll have to take the clutch apart again tomorrow and have a look for wear on the back of the pressure plate. What would the solution be though? Extra friction plate maybe?

Does anyone know whether there are supposed to be any friction 'pads' on the bottom of the chainwheel? When I look at SRMs chainwheel for a A7/A10 plunger, it seems to have friction pads on it. Mine doesn't have any there..
http://shop.srmclassicbikes.com/product/chainwheel-6-spring-inserts-a7-a10

[chaterlea25]

Hi Owain,
That's a swing arm 6 spring chain wheel not a plunger one

Check for distorted plain plates if you dismantle the clutch

John

[owain]

Ah yeh, so it is chaterlea25.

I think you were onto to something there Triton Thrasher. I just checked the service book diagram of the plunger clutch and I have correct plain plates...but I'm missing one friction plate. The pressure plate is sitting directly onto a plain plate. It seems very simple in hindsight! 

[muskrat]

G'day owain.
The pressure plate acts against a plain plate. 6 plain (the rear one is thicker), 5 friction plates.
The domed cover is to keep most of the oil out but a little does get in. If you use a multigrade oil make it a motorcycle specific type OK for wet clutches. Castrol Active 4T, Shell Advance AX5, Penrite MC-4ST or as others here ATF F type. If you have surflex friction plates they can run wet (cover off). Your friction plates may have been contaminated with the modifiers in the oil you used. A good soaking in petrol the dry and give them (both plain & friction) a light rub on a flat surface (glass) with 400 grit wet & dry. Grease is not a good idea in there.
Another quick fix is to put 1 or 2 flat washers under the springs in the cups. When tightening the nuts keep the studs just below the surface of the nuts and make sure the pressure plate lifts squarely https://www.a7a10.net/forum/index.php?topic=564.msg50805#msg50805
Cheers
I luv my plunger clutch.

[duTch]

 I'm not sure of the standard length the springs shoud be, but from memory I think mine are all about ~1,1/2" ( ~37mm), so yours may be a bit short and lost pressure. Being in Wales, you may be able to squeeze in a trip to SRM....

  I bought some new springs from ********, and they are wound the opposite of what came out, which may or may not matter so I haven't used 'em- but that's a different issue

 PS; I don't recall seeing any mention of you trip from the Continent but congrats you got it together and so far

[Triton Thrasher]

Ah yeh, so it is chaterlea25.

I think you were onto to something there Triton Thrasher. I just checked the service book diagram of the plunger clutch and I have correct plain plates...but I'm missing one friction plate. The pressure plate is sitting directly onto a plain plate. It seems very simple in hindsight! 

I don't know these clutches well, but the pressure plate is either kissing the clutch centre or it isn't.  If you remove one plain plate and the pressure plate can still press the plates together in a trial assembly, then that isn't the problem.

When you said it slips when you take off from a junction, that sounds so bad that it seems it must be something worse than spring pressure being a bit light, or a little oil on the plates.  That's what made me try to think of a positive mechanical reason.

Is the handlebar lever quite light to pull?

On a three spring clutch on another well-known make of twin, my Surflex plates always slipped if any oil at all got on them.  Re-lining them with cork matting and squeezing an extra pair of plates in fixed it.  Cork seems to be very good in wet clutches.  Yes I know- yours isn't wet.

[duTch]

 Not disputing what you say TT, but attached is a pic of my spare Plunger Clutch basket (complete with crusty phosphoric acid residue), but no springs, cups or plates

 Can be seen how low the pressure plate sits in the main basket.

 

.... I think you were onto to something there Triton Thrasher. I just checked the service book diagram of the plunger clutch and I have correct plain plates...but I'm missing one friction plate. The pressure plate is sitting directly onto a plain plate. It seems very simple in hindsight! 

 I don't think that's a problem;
 As Musky says the pressure plate is against a plain plate, which I maybe wasn't aware of when I dropped one friction plate out but figured it doesn't matter as they both run in the same splines so can't spin or go anywhere anyway...so going on that, I must have 5 plain plates (including the thick rear one)- fairly sure...

[Triton Thrasher]

Hey Dutch- you are disputing what I say and you're quite right.  It looks impossible for the pressure plate to foul the centre, in that clutch.

Are they all as deeply dished as that?

[Triton Thrasher]

Do the spring cups ever bottom out on these things?

[BSA_54A10]

  I bought some new springs from ********, and they are wound the opposite of what came out, which may or may not matter so I haven't used 'em- but that's a different issue

 PS; I don't recall seeing any mention of you trip from the Continent but congrats you got it together and so far

Do not use springs wound the wrong way on a 3 or 4 spring clutch because hey will allow the adjuster screw to unwind.
On an older clutch where you can fit lock nuts it dosn't mater but on the clutches with the mushroom shaped sleeve nuts they are a disaster.

[Greybeard]

Hey Dutch- you are disputing what I say and you're quite right.  It looks impossible for the pressure plate to foul the centre, in that clutch.

Are they all as deeply dished as that?

I'm pretty sure mine is not so far below the cage.

[duTch]

 

.......- you are disputing what I say and you're quite right. ........

 ...just usin' my best diplomacy 

 

Do the spring cups ever bottom out on these things?

 Good question, one that I've been meaning to investigate for some time- NOW is that time.....

 So here's some pics that show;
#1>    the inside of the Pressure Plate, and in the first two pics have inverted the Spring-Cups at the absolute possible (bottomed out), which shows in;
 #2>   the bottom of the Cups just level with the Pressure-Plate sitting accordingly Bottomed-out. 
  #3>   Third pic is the Cups in normal position,

  So my conclusion is; If the Cups were Bottomed out would be sitting a bit proud of the Pressure-Plate.
- obvious to see there's not much in it though 

 Edit; just measured the cups @ ~1.231"/31.25mm (underside of lip to bottom of cup) Cup-surface of Pressure-Plate to inside-Bottom of Clutch Inner = ~1.273/32.33mm , so There's about 0.040" (40 thou/1.0mm) clearance- not much to play with.
     That's on my spare anyway, others may be different , I'll measure my unit in use next time I have it off.....
 
 

I'm pretty sure mine is not so far below the cage.

 Shirley GB, if you took all the plates out it would 

 

Do not use springs wound the wrong way on a 3 or 4 spring clutch because hey will allow the adjuster screw to unwind.
On an older clutch where you can fit lock nuts it dosn't mater but on the clutches with the mushroom shaped sleeve nuts they are a disaster.

 I totally agree Trev, that's why I've never used 'em. I asked for opinion about this ages ago, but don't recall any feedback (until now )

[duTch]

 The other obvious possible outcome  of the above conclusion is out may be possible that tube chips have been replaced with longer incorrect ones...

[chaterlea25]

Hi Dutch,
How many plates in that clutch?
It looks like is short a few as the upturned cups are virtually level with the pressure plate??
I know that the centre will not be sitting against the chainwheel when on the bike
Take a pic of the plates stacked onto the inner drum, with the pressure plate and upturned spring cups

John