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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on September 03, 2026, 05:57:54 PM »
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!
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British Bikes / Re: After the rides done, wheres the best place to find someone whos just as keen on classic bikesan
« Last post by Rex on September 02, 2026, 09:30:13 AM »
There's the local Spam enthusiasts club; you might find that interesting.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on September 01, 2026, 06:23:04 PM »
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....
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British Bikes / After the rides done, wheres the best place to find someone whos just as keen on classic bikesand ma
« Last post by expatriot on September 01, 2026, 12:47:42 AM »
Ive been riding all weekend but my garages getting lonelyanyone know a good spot to meet fellow enthusiasts who arent just into the bikes?
 
 
 
MeetPrettyGirls.com
Real girls, real desire, real close
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rex on August 31, 2026, 12:15:14 PM »
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.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on August 30, 2026, 03:27:08 PM »
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....
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on August 29, 2026, 01:53:44 PM »
Quote from: Rex on August 28, 2026, 05:45:19 PM
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.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rex on August 28, 2026, 05:45:19 PM »
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.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by cardan on August 27, 2026, 09:11:00 AM »
Lovely photo of your dad with the bike.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on August 26, 2026, 07:00:16 PM »
This afternoon I staggered over to the workshop, (I've done something egregious to my lower back and I'm struggling a bit...  probably kicking the damned bike at the show on Saturday when the clutch was slipping...)

First was replacing the borrowed oil-feed nut with a new one.
I've got to take the old one back to the owner this week, so that's a job for tomorrow.


Then I drained about 400ml of oil from the tank - mainly to see if it stops it leaking oil down my trousers every time I ride it.  Ideally the tank should be baffled, ie have a tube that is inline with the filler hole, but it hasn't, and there's no baffles internally either (in both halves) so the fuel and oil both splash around while riding.  Something to think about for the future.

I then turned my attention to the clutch (again).  I've been doing a lot of research, and I think I've figured out what's going on.

Firstly - I'm definitely going to invest in a new clutch body, it's a peace of mind thing more than anything else.  Presuming I buy a "good" one, then it should last the life of the bike: I doubt if I'll do more than 500 miles a year on this thing!

But the rest of the clutch also appears to be made up from random parts (hey - just like everything else on this bike! :roll: )
Sometimes I think Dad made it up like this deliberately to tease me from beyond the grave!  Well, you old bugger - it's WORKING!!


The clutch is an AMC type, in that the friction plates interact with the body, and the plain plates interact with the basket (pre-AMC Norton clutches are the other way around). 
Going by the number of plates (back plate, drive plate, 4 friction, 4 plain, 1 single-side), it's "setup" as an ES2 / Dominator spec unit. 

HOWEVER: the pressure plate is NOT right - it "appears" to be a later one from the Atlas, which was specced with 2 more plates, and with thinner friction plates.  So - the Pressure plate is thinner.  This was so that Norton/AMC could still use the same basket, body etc etc parts while ostensibly "upgrading" the clutch.

I need to confirm this: I'm hoping to be able to get the thicknesses of the various plates from Andover Norton if I can get through to them tomorrow. I've looked in the Norton Owners Club documentation, but haven't found that information (yet?)

My pressure plate is ~0.7" thick (measurements: 0.692", 0.702", 0.692")


I also measured the springs, and the spring cups:


Spring cups:
Overall, "Effective", Lip
1.592" : 1 19/32", 1.525" : 1 33/64", 0.55
1.557" : 1 9/16, 1.497" : 1 1/2, 0.55
1.563" : 1 9/16, 1.502": 1 1/2, 0.55

So - one of them is longer than the other 2.... :wtf:

Springs:
1.70",
1.70",
1.692"
Nominal is (according to NOC), 1.78", so they're all a little short (not by much though).



Spring cups in the recesses:


I reassembled the entire thing with all the plates so I could check the offset from the body to the underside of the pressure plate


Without fitting the spring cups and springs (obvs!)


I'm actual looking at the gap between the pressure plate and the central clutch spider, because that's the closest part.
That measurement was 0.25"

The thickness of the pressure plate?


0.225"

So - the gap without spring cups and springs is only 0.025"

I'm hoping that a proper Dominator type pressure plate has a similar "thickness", but an overall height of greater than 0.7" (45/64" or therabouts!)

I also measured the nominal depth of the recesses the spring cups sit in:


"Approx" (the base of the recess is curved) measurements are:
1.4875" = 1 31/64
1.49" = 1 31/64
1.532" = 1 17/32

So - pretty damned close to the overall length of the cups - if one or two isn't bottoming out, I'd be very surprised.

I need to find out what the nominal correct length for the spring cups is, and then decide what to do.  It could well be that a Dominator pressure plate, and a new Body will solve all the ills.  While I'm replacing things I may as well replace the cush rubbers too (mainly because I have a feeling that getting the current ones out will be a somewhat destructive process... ahem...)

Thinking about it - I reckon that with brand new clutch plates (ie, the correct full thickness of about 4.5mm, mine are all between 4.2 and 4.4mm), the clutch would "just about" be ok - the offets and gaps would be "just" open enough to not cause slippage.

I'm going to bring the clutch down the Selsey JAP man just to get a 2nd opinion, but I'm fairly confident that getting a new body and pressure plate will be the solution, so tomorrow afternoon may well mean a bit of wallet furtling...
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