Clutch Pull and Clutch Stack Height

Have we ever had a clutch thread? No? Didn't think so.



So I was getting a little weeping from the primary on my Interstate. No belt drive. Not yet.

When I was in there I noticed a bit of play with the clutch basket. Going the cheapest route I replaced the bearing. That snugged it up a little bit. I really suspect a warn clutch hub center.

Then of course there was the issue with the plates. I remember when I first got the bike I think it had the bronze plates. At some point they were replaced with Barnetts.

Well, they didn't look good.



Now I have new plates in there and I'm checking the pull. It's slightly better than before (which wasn't great). Most interestingly was the old plates were the same thickness, so no apparent wear at all. Well, aside from the teeth.



So with the new plates this is what the clutch looks like. That doesn't seem right as there's no room for lift, right?

But then when we look at the spring it's flat (as much as I can tell) when engaged. All my reading says that it should be slightly inverted or flat. So I think it's right where it should be.







When I check out my 750 which has the perfect clutch it's actually extended (dished in) slightly when engaged (which would indicate a shorter stack height).

The best I can tell is that I need to lower the stack height on the 850. Do I have this right?

concours said:

ndnsclutch

dynodave Clutch Pack for Norton Commando - Atlantic Green Technical Services - British Motorcycles

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Yeah, read through it several times.

Also many threads here.

Dave says to have it slightly inverted (bowed out). Comstock said he likes his flat. And on my 750 it bows in and feels great.

If there was one right answer there wouldn’t be a need for more questions.

I've jacked with mine endlessly and pretty much settled for not having to use a crowbar to operate it, although it is in or out with no easing for takeoff. I can live with it because there's no slipping, so good and bad equally.

jbruney said:

I've jacked with mine endlessly and pretty much settled for not having to use a crowbar to operate it, although it is in or out with no easing for takeoff. I can live with it because there's no slipping, so good and bad equally.

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i might be there with this one too. I’ve tried different combinations of the spring either in, flat or out and they all don’t feel great.

I wonder if my spring is worn out. No matter what I try I can’t get it to overcenter.

You CAN get a clutch to be both easy to operate and non-slip. I have seen Norton clutches take effort that ranges all over the place from two finger operation to needing channel locks to pull the lever! My 850 had quite a stiff clutch when I purchased the bike in '06, though not as stiff as the lever on my original '71 back in the day. When I rebuilt my 850 clutch later, I did the adjustment/setup per Old Britts instructions and, unlike my original Commando, the clutch requires very little effort and does not slip. I got several adjustment steels from OB, found the one that gave the proper stack height and "Bob's Your Uncle" ever since.

The spring does wear out but takes a very long time I had to replace mine about 10 years ago after 36 years as well the clutch center hub, I am still running my original clutch plates and is a very light clutch pull, well its always has been a light clutch pull since new so maybe yours has gone past its use by date, things do wear.

Ashley

With 5 Barnett plates and 4 steel plates my stack height (measured to the highest part on the pressure plate) is 1.148”. Dave says it should be 1.172”. With an extra steel plate I’m around 1.22” and it’s a little better. But no combination is giving me an “over center” sensation. To torture myself I grab the 750 lever and it’s two fingers.

Have you measured your clutch rod length?

How does your actuating arm and roller look?

swooshdave said:

Dave says it should be 1.172”

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NO dave does NOT say "it should be"X

X is the beginning dimension of the components which make the current STACK HEIGHT .
In my article with the graph some folks measure then correctly use the basket depth dimension to adjust to a new stack Y height with the desired result of a extended/flat/inverted.diaphragm condition.
Y is what you have determined to be what it should be.
Since BDM leaked there are 3 versions of diaphragm spring, only by a spring measurement as in my chart can you know better what you are dealing with.
Otherwise a hand grenade approach using flat as a good characteristic reference is the usual method the add or subtract to a new stack height.
Remembering that .050 stack height has double the effect on my spring rate chart which is shown @ the clutch center and the resulting pounds of thrust on the pressure plate is also double.

dynodave said:

NO dave does NOT say "it should be"X

X is the beginning dimension of the components which make the current STACK HEIGHT .
In my article with the graph some folks measure then correctly use the basket depth dimension to adjust to a new stack Y height with the desired result of a extended/flat/inverted.diaphragm condition.
Y is what you have determined to be what it should be.
Since BDM leaked there are 3 versions of diaphragm spring, only by a spring measurement as in my chart can you know better what you are dealing with.
Otherwise a hand grenade approach using flat as a good characteristic reference is the usual method the add or subtract to a new stack height.
Remembering that .050 stack height has double the effect on my spring rate chart which is shown @ the clutch center and the resulting pounds of thrust on the pressure plate is also double.

Click to expand...

I apologize, I should have said “starting stack height”.

I was wondering how many different springs did you test to come up with your chart?

Also is there something I should be looking for if I’ve adjusted my height so that I’m either starting at concave, convex or flat and still can’t achieve the overcenter feel? With my 750 is was clear I could get to a super light lever and slipping clutch. And then dial it to a perfect feel. But with the 850 it’s just varying degrees of stiff.

"Varying degrees of stiff"..... You mirror my thoughts after very much sweat and piddle. I gave up and made peace with it before wearing out my spring depressor.

swooshdave said:

I wonder if my spring is worn out. No matter what I try I can’t get it to overcenter.

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What have you tried? You haven't mentioned shims. In my experience (2 bikes), adding an extra .080 steel plate resulted in the spring "snapping" over center early and making for light pull but a slipping clutch. Reducing the shim plate to .065 put both clutches in the sweet spot.

And FWIW, I bought a spring off eBay just to see... and it was exacly the same as my stock one.

I increased the stack height on my 750 as per Atlantic Green article and clutch still felt stiff.
By pushing on the Clutch actuating rod With a finger and pushing back on the clutch operating arm in the gearbox With my other hand, I could feel that the movement was binding even without all the pressure of the clutch spring acting on it.
I bought a new arm, clutch op roller and sleeve.
when I compared the new arm with the old, I was amazed at how much had worn away. It didn’t look worn because the wear was round from the roller. I wish I had taken pics - too keen to get it fitted and give it a go, I guess.
Anyway, after this clutch operation was smooth and lighter.

Not Saying this is your problem, but it is simple to check how easy the arm operates the Rod by feel.

SteveC said:

Not Saying this is your problem, but it is simple to check how easy the arm operates the Rod by feel.

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This, plus the obvious release arm alignment with the cable entry in the gearbox, and the cable routing. I also got significant improvement after switching to a teflon lined Venhill cable.

I get most relief when striking 4th for long periods....Heh heh..... Sorry about that, but far too much else needs attention to force the beast to keep the road.

This may be obvious information at this point but I will bust out my 2 cents anyhow.

A month or so back I snapped a cable 100 miles into what was to be a 400 mile roundtrip ride. Luckily I had a spare cable and completed the trip with some minor modification. I enjoyed the heavy pull of my lever, but it was taking its toll on my cables so I HAD to solve it.

Just this morning installed CNW easy pull clutch, turned my cable snapper into well, an easy pull.
No slip, no drag, neutral slips right in. I will miss my Ulysses bow of a clutch.

I too tried all manner of cable routing, arm checking, stack measuring and plate adding before calling it quits and spending the money.

Hope this helps someone.

maylar said:

What have you tried? You haven't mentioned shims. In my experience (2 bikes), adding an extra .080 steel plate resulted in the spring "snapping" over center early and making for light pull but a slipping clutch. Reducing the shim plate to .065 put both clutches in the sweet spot.

And FWIW, I bought a spring off eBay just to see... and it was exacly the same as my stock one.

Click to expand...

I’m trying various combinations of plates just to see if I can get an acceptable pull.

Old Britts only has one shim plate available anymore.

Cable entry into the gearbox looks good. One of the oil lines was pressing on the cable so I adjusted that. No difference.

Cable routing looks good.

I don’t like the cable so I’ll replace that. And probably the actuator at the same time.

FYI.
RGM do 3mm and 4mm pressure plates.
Hope you work it out.