Troubleshooting a JAP Special

[Rex]

On your pic of 21st August it appears that it would be possible to screw the clutch nuts down a bit tighter. Have you tried that or do the springs become coil-bound?
Did your dad have the bike running satisfactorily or was the clutch always problematic?
I've had bikes in the past where the clutch springs have measured up OK but still been useless. I suppose that comes with people using what they have rather than buying something known to be suitable for the power expected to be transmitted.

[Rockburner]

On your pic of 21st August it appears that it would be possible to screw the clutch nuts down a bit tighter. Have you tried that or do the springs become coil-bound?
Did your dad have the bike running satisfactorily or was the clutch always problematic?
I've had bikes in the past where the clutch springs have measured up OK but still been useless. I suppose that comes with people using what they have rather than buying something known to be suitable for the power expected to be transmitted.

While balancing the clutch springs once or twice they did get screwed in further, however I think the cups were bottoming out. It would certainly explain why I could see the pressure plate moving outward while pulling the clutch lever, and one of the cups was stationary until the pressure plate had moved a sixteenth or so.

From memory the clutch has always been ok, but I wasn't always privy to all the information from the riding the bike had. (Track days etc). It does follow the"philosophy" of the bike's entire build that the clutch would be built up from random found parts that didn't necessarily all match up correctly.

I've got proper pre-63 pressure plate on order, and a line on a replacement hub, so at the moment just waiting for things outside my direct control to happen.

[Rockburner]

A light session today, awaiting clutch parts and my back is still problematic.

I stripped the clutch down completely, which involved, some gentle persuasion:


But it was all good in the end.



I cleaned up the parts that are going to be reused, including a good 40 minutes of gentle filing of the outer part of the central spider and the plate that slots over it, the spider has presumably had a hard life and it's a little "peened over".  Which is one reason why the Thor was brought into play....

Tidied up all the clutch bits: plates, reusable components, components being replaced:



I also span on a new bell-mouth for the carb:


Alledgedgly a long intake increases torque...


That's it for now: awaiting a new clutch body and some other items that I've ordered.  I also need to file down the spring cups, they're somewhat battered, but that's a job for another day tbh: I had an idea for clamping them up in something tapered so I could spin them in the drill, but right now I can't find anything suitable.

If I ever get down to 2 bikes in here I may well invest in a lathe....

[Rex]

Good idea; old Myfords, like old bikes, are dropping in price all the time.
What was the thick end of £1k a couple of years back is now unsold at half that.

[Rockburner]

Still waiting for the new clutch hub to arrive, but some other bits turned up.

New pressure plate is 0.915" "high" so a good 0.2" higher than the old one, should be good.


new rubbers - they're "shorter" than the originals, by about 5mm~ish but I can't really see a problem there, they should still do the job, they're captured on both "ends" of the clutch body so it should be fine.


I also got some new stud nuts so spent an hour or so just spinning a die up and down the stud threads to clean them up.  If you can spin a die down a thread just using your fingers then you're not going to be damaging the thread (unless it's utterly kaput):


Also did the spring nuts, again, if you can spin it down with your fingers, then the thread is correct and you're not cutting it anew.


Then I went looking for a 1/2" bolt or stud for the new pressure plate.... because it's a got smaller hole for the adjuster grub-screw!!


Annoyingly I could find anything at all (well, there's a couple of old bits of knackered stud... but: ) and also not sure what the thread is: so - will likely just order something that is guaranteed to fit from the same supplier.

hey ho....

[Rockburner]

The new clutch hub turned up today so I went and did some fiddling!


With the clutch you perves!


New hub looks the part:


Slots into the stack nicely


This should be fun....


C-spanner, gearbox in first, brake locked on....


All in with remarkably little swearing! Many thanks to iansoady suggested the C-spanner method.


Then I did some tinkering and playing about with fitting things - I bolted up the back plate and the race-plate so that I could be sure the central spider was in place fully. (sorry, no pics).

I've discovered that 2 of the studs are bent, so I'm getting new ones while the clutch is in pieces and I can fit them quickly.  But the old ones sufficed for a reassembly test.

Then I turned my attention to the spring cups.  I think with the deeper pressure plate they're not going to be bottoming out, but they could do with a clean up and I figured out a way to do it.

Behold... scrap.


And yet... assembled in the right order... this spring cup is ready for a spiffing.


Who needs a lathe?


Take it easy, and nothing will be damaged...


Bit of P600 to smooth it off.


Pre-spiffed, spiffed, and desperatly needing a spiff


Good enough for me.



Probably not going to make one iota of performance difference, but it was satisfying to do.



and I just nearly caused myself a panic attack by thinking that I'd got the rubbers in the wrong way around... but comparing this view of the BACK(inside) of the clutch body:


With this view of the FRONT(outside) of the body:


You can see that the rubbers are in opposing positions.... as you would expect!

Phew!

[Rockburner]

I managed to get an hour in the shed on Sunday, and the rest of the clutch bits had turned up from Andover Norton.

New, (straight!) studs


Adjuster screw and locknut


The first thing in the clutch assembly (after the rubbers and the outer plate) is a tiny bit of "anti-centrifugal grease" on the clutch bearing.... I couldn't find any information on what constitutes "anti-centrifugal grease", so I dug out the high-temp lube I use for brake pads etc.  I'm going to use an extremely small amount, so I figure that all it needs to be is capable of withstanding high temps and not flinging.

The bearing "inner" is the outer diameter of this plate:


Told you I wasn't going to use much.... (actually I used twice that...)


Bearing half-assembled


Studs into the clutch body: they're keyed to semi-squared holes in the bearing race plate so they don't rotate.


Assemble the rest of the body, and don't drop it....




BUGGER!


Try again.
Lastly fit the stud nuts on the back


Clutch body onto gearbox layshaft with washer, lockwasher and big nut


Big nut is the same size as a spark-plug


Again, without having the proper clutch holding tool, I have to resort to using the rear brake to lock the layshaft (via the final drive and gearbox)


I bet myself I could get the stack on in one go.... YAY!


Then I freed off the clutch cable as far as it would possibly go to give myself plenty of slack to work with while getting the setup right.  Ideally, the lever in the gearbox needs to be "over-center" so that the cable pulling it has plenty of room to work.  That means the lever need to be as far away from the gearbox inner as you can get it.


Lots of slack...


Even more slack - from freeing off the handlebar-lever adjuster


The push rod is now a "long" way into the layshaft when "at rest"


And the lever is as far "out" as it will go (probably too far tbh!)


Then fit the pressure plate, spring cups, springs, spring nuts.  The advice is to screw the spring nuts down until they are "flush"


What is supposed to happen next is that you adjust the screw on the pressure plate and the clutch cable adjusters so that although you have a bit of slack (either 1 or 1/2 turns back on the pressure-plate adjuster: advice varies) to allow for thermal variation, and the clutch lever has a nice pressure on the clutch.  Bearing in mind that the push-rod lever needs to be "over-center" and not fouling the inspection cover.

However... to get any where near that state, I had to screw the adjuster screw in so far, that the lock-nut wasn't going to work: even this wasn't engaging the push-rod.


Obviously, with a pressure plate that's about 1/4" deeper than I had before... I need more length in the rod (ooer), or some other way of taking up that gap in the mechanism.

At least enough to give the locknut a fighting chance... It should look like this.


Obviously it took me a few minutes to puzzle that out though, I thought I'd gone mad.

The last thing I did was pull the push-rod out again... and it's covered in oil.


Which confuses the hell out of me - I'm sure I put it back in clean, and the oil is fresh clean stuff, (obviously, since I changed the oil) so - given that the layshaft tube is much higher than the oil-level in the gearbox and the mods I've done are supposed to stop this... the only conclusion is that my mods didn't work. BAH!

I may look at fitting a larger diameter breather , or possibly just drilling out the jet that's fitted (off the gearbox, obvs).  but the sheer amount of oil on the layshaft is really confusing to me.  The way the oil supposedly gets in there is a "oil-mist" when the box is hot and the internal pressure pushes the air/oil mist in there out of whatever exits it can find: the clutch cable is one exit, the push-rod-tube is another, and the blow-hole on the original inspection cover is a third. The idea of fitting the extra breather is to increase the number of exits and so reduce the propensity of the oil-mist to  get where it shouldn't (down the push-rod-tube!).

These clutches do normally, ie, by design, run in an oil bath (the original primary cases on Nortons contain an amount of oil (Not sure huow much, and it seems ATF is preferred, makes sense), mainly to lube the primary chain, so any gearbox oil lost down the push-rod-tube probably isn't really noticeable.  But I'm running this clutch dry (although I think it's got plates that "should" be ok runing wet), so the oil seepage is a lot more noticable, and I was thinking that it may have been what caused the slipping - although I'm beginning to wonder if the oil seepage was just incidental and not the main cause of the slippage.


So, steps in the right direction, and yet more choices to make.

Regarding the push-rod, I'm thinking that tbh, the easiest way to fix this is going to be a longer pressure-plate adjuster screw, so I'll be taking measurements and seeing what I need to find to achieve that.   
Oddly - ther appears to be 2 options for this, but I've only found this reference in one place (so far).

040360: Adjuster, in press. plate. All. Short (5/8”).
061179: Adjuster, in press. plate. Long (7/8”) Norvil, Dom, Comm

So - I'll look into that.

Some advice I've read is to put a 1/4" ball-bearing down the tube as a "spacer/extender", and I may look into that if I can find one in all the junk I've got.  There's already a ball-bearing as part of the push-rod-lever :


Again - an option.

So, plenty to keep me busy....

[cardan]

There's nothing magic about the push rod itself: you can make a new one with the correct length from silver steel, with the ends hardened (heat to cherry red and quench in oil). Usually if there's a ball, the push rod is in two pieces and the ball is in the middle - it will try to fall out is it goes at either end of a one-piece rod.

Leon