Early Dommy clutch lever question

Re very early lay down gearbox Dommy.
What is the correct distance between the clutch lever pivot point and cable nipple centre point?
A friend asked me (to which I replied how the hell would I know)as he cannot get a customers clutch to free off correctly.
He has checked everything we can think of including my sending him a new worm lift mechanism..... which is the same as is fitted....the ONLY thing left is the clutch lever.....AMC employed 7/8 inch levers...Commandos 1 1/16 inch levers....did those early Dommys employ 1 1/4 inch levers??

In theory the early Norton dommies used 7/8" levers, although you don't often see the originals on too many bikes these days.

Other possible causes of problems with freeing the clutch off are a notched or worn drum, the adjusting bolts done up too tight
(they are not just tightened fully down, but must find the balance point) and the clutch rod being stiff inside the gearbox mainshaft.
1/4" rod is too big, Nortons used 7/32". And the mainshaft was drilled from either end, and sometimes doesn't meet too neatly,
so watch that this can cause problems.
Norton clutches also entirely used friction inserts, not cork inserts, if any have strayed into the clutch this also may cause problems.
New plates that are thicker than stock may also eat into the little available clutch travel, and cause freeing off problems ?
hth.

Further... The bike being played with is in Birmingham and I live in Essex...for my sins.
As I understand it the bike is an early Model 7 with laydown box with the wirm lift mechanism. The box has a markin of G102 which a friend tells me is a gearbox for a 16H /Big 4.....just to confuse matters further IF he is correct and I suspect he is. The Gent doing the playing is an Engineer who makes a good living manufacturing Norton bits for various people along with repairing rebuilding Norton lumps etc. He sometimes uses me to do investigations knowing that in my retirement I have nothing better to do...which is true these days!
With the clutch removed and a clock gauge on rthe pushrod with a 1 1/16 clutch lever fitted the total lift is, I was told a few minutes ago, approx 0.050 inch. The clutch will not free off corectly and drags. THe clutch has been fitted with NEW interplates and Surflex friction plates. The original interplates were badly 'blued up' possibly indicating that it had been sufffering drag problems previously (or slip problems due to oil entering the clutch burt it should have an OIL EXCLUDING BAND around the basket to reduce this problem. Note I said SHOULD HAVE....
The Worm lift mechanism is in good condition. Pushrod is correct etc etc.
I was told by a Chief Clutch Designer that as a good rule of thumb that for moulded friction materials then for good drag free freeing off one needs of the order of 0.005 inch per friction interface so assuming 10 friction interfaces pahaps one the friction material beds in the clutch will be drag free BUT if the correct clutch lever should have 1 1/4 inch between pivot point and cable nipple the lift will be a bit greater..........
So what is the centre distance of the clutch lever originallty fitted???????
I can hardly phone the olde Norton people who would probably know because like so many of the real EXPERTs in my address book they are no longer with us.......alas. I bet Phil Heath would of known or even John Hudson or even Mr Hopwood. One day I really must sort out a new address book as this old one is so depressing to look at...all that Norton knowledge no longer with us.
Anyone out there with an in theory original Model 7 ?????

J.M.

Frankly, I have no experience with a Model 7. That said, my Atlas AMC clutch lift mechanism with 7/8 " lever centers, provides at least 0.05" of lift at the pressure plate. My primary is closed up now, so I cannot verify, but I had it open a few months ago, and rebuilt the clutch, so it is fresh in my memory.

As an engineer, based on "guts", I would say 0.05" with 1 1/4" lever centers is suspiciously small. However, if you can get that much lift, the clutch should free up, or at the very worst, drag somewhat.

Let me relate my recent experience ... perhaps it applies to your friend's case.

As I said, I rebuilt my clutch ... new spyder, center body, friction and plain plates (Barnett). While I pursued other refurbishments on the bike, considerable time passed (more than a year). When I tried to free up the clutch, the pressure plate was lifting about 1/16" but the clutch was locked tight ... I could kick over the engine if I cared to, with the lever pulled completely in. I found, on complete dis-assembly of the plates, that time had stuck the friction plates to the plain plates, effectively welding up the clutch. There were 2 or 3 stuck pairs, but it only takes one pair to lock up the clutch. Now I pull in the lever and operate the kickstarter on a weekly basis.

IHTH

Slick

I'd be pragmatic. If it appears to need the extra lift of a 1.125" lever, try one.

If that makes the clutch too heavy, back off the springs. If that causes slip, what can I say, except that you were right all along about British bike clutches!

Triton Thrasher said:

I'd be pragmatic. If it appears to need the extra lift of a 1.125" lever, try one.

Click to expand...

Good advice.
Too much theorizing by JM there, just get it working.
I currently have 4 Model 7's, although mostly works in progress.
Bought my 1st one as a schoolboy, learned a lot from that, everything was knackered...
I would have said a 102 box was quite possibly original to the bike. The NOC LIbrarian may know, if you quote the VIN number.
The handlebar levers originally were 7/8" pivot length, although it makes very little difference, they don't seem to be fussy.
The clutch, with a good cable is very light to lift, always surprised me it had enough grip to work, but they do.
Surflex plates may be thicker than original, could cause problems.
If the plates are warped or bowed, could cause problems too, from loss of lift.

P.S. I may have omitted an important detail, that is in the manual.
The 3 spring clutch plate should lift evenly and squarely.
If not, it may cause dragging or poor disengagement.
The bolts should be adjusted so it lifts squarely and evenly...

Yesterday I received a call from the wilds of Birmingham ... The problem is solved and had sweet b****r all to do with clutch lift. The bike owner was simply incapable of adjusting the drive chains correctly and the rear chain was over tensioned which I suspect was causing the mainshaft to run tight against the new sleeve gear bushes. Anyway once the friend in Brum adjust the chains correctly the problem had gone...... He has, I have been assured, given the bike owner a lesson on how to CORRECTLY adsjust the drive chains and explained to him how the greater torque in the secondary pulls everything back towards the rear end resulting in tightening up and often over tensioning the primary chain(breaking chain rollers and sometimes the chain!!).
Pahaps I was lucky in being taught at a very early age how to correctly tension my drive chains...the primary first with ones heavy hoof pushing down on the secondary chain pulling everything back towards the rear end and only them adjusting the secondary chain.
A few years ago I asked a Gentleman the following question..not word perfect ...' In your opininion with your many years of experience in the design, development and application of toothed belts etc and industrial belt drive systems what effect on belt life does incorrect tension have?? The Gentleman as is often the case replied 'Ah I can do better than that because we conducted testing on this very subject many years ago..the results will be in deep hold store somewhere but I can probably find them and send you a copy if you want but basically we found that a correctly tensined belt will have a life 3 to 4 times greater than that of an incorrectly tensioned belt. My money is on exactly the same applying to chain drives and my memories of the vast numbers of second hand primary chain cases sitting on the shelves in Motor Cycle Shop in London years ago is that the great majority had chain grooves showing suggesting that the average owner was not even capable of adjusting their chains correctly. MIND YOU a Triumph Service Manager once told me that the ONLY reason for removing the crank oil seal on the later twins was because of the great number of bikes coming through the service dept and being found to have rusty damn nigh solid primary chains due to the incompetence of the owners so it was decided to lubricate the primary chains automatically - TILL THE OWNER ALLOWS THE MOTOR TO RUN OUT OF OIL THAT IS!

Good he got it sorted then, even if we hadn't even covered that bit - yet !

One of the guys in a bike wreckers once mentioned that 'most' of the bikes they get in were probably due to a lack of oil,
so its certainly something that afflicts even modern bikes....

Early Model 88 have solid leave type and with a 7/8th pivot Has I own one, of a 1954 vintage

Do the early Dommy's have the steel clutch plates with a V on the bottom tags or are they all square?