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!