classic motorcycle forum

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....

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.

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...

I wouldn't know a BSA clutch from a bar of soap, but I'll give my 2 pennethworth. !

The band around a Norton clutch is intended to keep oil out of the clutch plates.
As long as they are not flooded in oil, they work perfectly satisfactorily without the band at all.
A trace of oil on the plates is not the disaster it once was.

Norton clutches came in 3, 4 and 5 plate versions.
A 750cc would need the 5 plate version if you expect the clutch not to slip.
A 350cc might get away with 3 plates, but you'd have to be able to assemble and adjust it  OK.

Binding when you do up the retaining nut usually means the clutch basket is rubbing on the bushing in the high gear bizzo,
maybe even pulled up hard against it.  You may need some sort of washer or spacer to hold it out slightly further on the shaft.
Could be the clutch is machined slightly differently or deeper than the original. This MUST be corrected.
How is the chain alignment. ?
Hopethishelps.

A 12" coarse file, which has a name that the site thinks is not ok to publish.

Leon

Ah yes - the good old illegitimate offspring file.  Gotcha.