classic motorcycle forum

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.

I think you're barking up the wrong tree with that worn clutch centre; if you think it's an issue then simply take a 12" !"£%^% to it and smooth it out. The worst that will happen is that it would rattle slightly more when the clutch is pulled. Hardly a concern.
Usually they're worn much more than that, and the main symptom is a dragging clutch leading to crunchy gear engagement when pulling away.
Don't really see how the minimal wear you have there will/would cause clutch slippage within 50 miles or so.
£330 quid is a bit much for suck it and see diagnostics, too. I'd be looking at plates, springs and something amiss with the assembly first.

Well, this is the dilemma. I am struggling to find anything "else" that could be wrong.  The plates aren't too worn, the assembly "seems" ok, there was sufficient play in the push rod that I'm sure it wasn't causing slippage. The springs seem strong enough.... What else is there? This is the first time I've tried to get a Norton clutch working, and I'm not familiar with clutches in general anyway, so any specific ideas will be welcome.

Oh, and a 12 inch what?

Last night I made my (poor) excuses and got out into the shed again.

I pulled the clutch apart and put the plates into some petrol:



While I tried to get my head around this flaming washer.  The local JAP man, who races JAPs in cars and bikes, and has a Manx engined F500 car, which uses a Norton gearbox and clutch, told me that there SHOULD be a washer between the clutch and the gearbox, and (after some detailed discussion) imparted the knowledge that is should be sittingon the OUTER shaft, not the INNER shaft - the gearbox output and input shafts respectively.

NB: the gearbox input shaft rotates INSIDE the output shaft (they rotate in the same direction, but at different speeds).

This mystical washer, according to local JAP man, should sit on the OUTPUT shaft and essentially serves (it appears) to ensure an offset between the clutch and the gearbox output sprocket.

The thing is... this makes no sense to me at all.  Because the clutch has a splined fitting on the end of the input shaft, and that fitting is both tapered, and has a solid stop.  If you do the clutch up tight (without the washer), there IS an enforced clearance between the back of the clutch, and the end of the output shaft.  I simply can't see the need for a washer, the clutch can't bind to the end of the output shaft.

... and besides - if the clutch was NOT supposed to go up tight on that taper, and wedge itself in place under the nut.... WHY would everyone be selling a specialist "Clutch Removal Tool" specifically for pulling the damned clutch OFF that taper??  :wtf:

I pulled the clutch back plate off and fitted the body of the clutch by itself onto the gearbox input shaft:


It's not that easy to see - but the washer is free to rotate with the clutch body tightly screwed on:
https://youtu.be/yYCOc3h9h3A

So - why do I need a washer there???


When the clutch back plate is fitted, and the stud nuts are in place - that washer fouls the stud nuts (it's worn them away in part - as you'll see later - which can't be right).

I cleaned up the studs and the nuts :


Took the race plate and the roller bearings out (yes they went everywhere, and yes I swore a lot, and yes I lost one .... found it again eventually...)



The rubbers still won't come out - but at least I was able to have a sort of evaluation of them - they seem pretty solid still, there's some debris in there  - but not a lot really.


Gave the studs a good brassing: (I gave everything a good brassing!)


Failed to count the roller pins propertly ....  twice...



Back plate, race plate and main body



In all honest - I think this is the real problem:


The dogs on the clutch body: which is where the friction plates act* are battered quite badly.



* : power from the engine comes into the clutch via the "plain" chainwheel plate / basket. 
The other "plain" plates are roated because they interlace with the walls of the basket
So - the "plain" plates are the "driving" plates, carrying the torque from the engine
The Friction plates are pushed against the Plain plates by the springs
The Friction plates are then rotated by that interaction, and
the Friction plates then bear on the clutch body in order to transfer the torque from the engine into the cush-drive rubbers.
The Rubbers then absorb some of that "impact" before passing the torque to the spider in the centre of the clutch,
The Spider has a splined/tapered core which slides onto the end of the gearbox input shaft.

Thus the engine torque is transferred to the gearbox (with some minor losses)

So - the battering that the clutch body gets: would tend to happen when the clutch is "engaged" and the throttle is opened hard and quickly.

Hmmmmmmm.


I carried on with reassembling the clutch body anyway.



These are the battered stud nuts on the back plate, they're a git to work on because they're so flat, knackered, and the back plate has dished areas so getting the spanner on them is very hard (I don't have a 6-sided socket in that size). You can see where the washer has worn away the flats - this is another reason why I don't think the washer should be there.


With the clutch body assembled, and the pressure plate installed:


In this assembly: the pressure plate is NOT hard up against the outer face of the clutch body.  The spring cups HAVE bottomed out, but the plate rattles about (the clearance is less than a millimeter I'd hazard, but it is there)

This is the washer in question sitting on the input shaft... it's NOT large enough to go over the output shaft


Here you can clearly see the output shaft and the input shaft inside it. The pimple sticking out of the input shaft is the clutch push rod which pushes against the underside of the pressure plate (there's a large grub screw in the centre of the pressure plate to allow adjustment: the push rod needs to have enough space to accommodate thermal expansion and have some free play, otherwise the pressure is taken off the plates and you get slippage).



I still don't "get" the washer at all, and I am very concerned that the main clutch body is beyond usage due to those battered dogs/splines.  A new one is around £330 (https://andover-norton.co.uk/en/shop-details-2/15111/clutch-centre-hardended-and-ground), and that would likely entail new plates (~£15 each: 9 of, ) etc etc ..... and you're building up to nigh on new clutch territory.... which is around £830-£950 or so....



Or spend the next 6 months wandering around autojumbles hoping to get lucky, and/or dealing with 2nd hand ebayers and who knows what will turn up in the post....



hmmmm

Current plan is to get a second opinion on the clutch body by taking the dissassembled clutch down to Selsey; and not get too far ahead of myself in the meantime.  The Selsey JAP guy did tell me on Saturday that he spent £400 on something and it was the best £400 he ever spent, but I didn't quite catch what it was that he'd bought, I just know it was something for the clutch!

What confuses me about the worn splines on the clutch body is: that can't have happened suddenly over the first 50 miles or so since I got the engine back in the bike ... it must be pre-existing wear (I'd imagine it would take thousands of miles to do that sort of damage), so why did the clutch only start slipping about 30 or so miles ago?  It's very very obvious when the clutch is slipping, because the kick-start torque goes through the clutch - if it's slipping, the engine will NOT turn over!