heavy clutch/ stack height (2015)

without going into one of the forum marathon replies, please can somebody give me the correct stack height, clutch plate thickness. my bike is 1976 850cc elec start model. the lever has got heavier and heavier, I have taken the cable off, (seems to run ok) gearbox cover off to check the clutch body lock (it was suggested they can become loose) the plates are now removed for inspection. I am confident with spanners but it is great when you have been there before and this is my first time delving into the Norton engine or any bike engine for that matter. thanks Neil

Check the angle of the clutch arm is 90 degrees to the cable, if the clutch centre adjuster is screwed in too far or out too far the clutch arm/ cable angle can change.
how
HAve not had this trouble on the Notton but have a Suzuki (sorry) GT250 that my son races. Could not understand why the clutch needed two hands (nearly), just told him to man up!
Eventually found the cable/ arm angle all wrong. Adjusted, magic, light clutch.
Hope this helps.

DynoDave and forum searches has the stack height(s) to seek * but varies per type of spring and gear box gasket crush and main shaft shimming. My down/dirty way is mix match plates till spring just slips into groove against the stack. I like both my Combat clutches ease and holding to catch rubber on sharp shifts w/o hint of clutch slip and nil notice of lever effort. My modern SV with spiral type clutch mechanism is not as easy nice nor as long lasting a clutch opening mechanism. Measuring will only be useful AFTER you have a nice stack but just going by numbers may leave you pulling hair out. Generally stack is fine tuned by thickness of pressure plate - depending on the new or old friction plates you have to work with. I have 3 thickneseses of pressure plates on hand, one of them the thickest is Alu.

mudplugger said:

without going into one of the forum marathon replies, please can somebody give me the correct stack height, clutch plate thickness. my bike is 1976 850cc elec start model.

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It isn't quite that simple, as variations in manufacture and subsequent wear of the components including the clutch drum must be taken into consideration. The correct stack height for one Commando clutch wouldn't necessarily be correct for another-so the stack height needs to be determined-either by measurement or by trial and error (fitting plates of different thicknesses etc). Also lightening the pull lessens the clamping force so lightening the clutch action can be a trade-off against grip.

According to the information on the atlanticgreen website, the late (5 friction plate) clutch stack height is 1.172" http://atlanticgreen.com/clutchpak.htm however, if the clutch drum backplate has worn down-then the original 1.172" figure may no longer be "correct".

What I suggest you do, is remove the diaphragm spring (leaving the stack in position) and set the spring to "flat" using the clutch spring compressor tool, then, holding the spring in position against the pressure plate, measure the distance between the spring and the circlip groove as demonstrated in the Old Britts article: http://www.oldbritts.com/ob_clutch_info.html as this will tell you approximately how "low" the stack height is from the "flat spring" condition (in the Old Britts article this is shown using a ruler, however a better way in my opinion is to reinstall the large spring locating circlip and then measure the gap between the spring and the circlip (using stacked feeler gauges etc.).

Sorry that isn't the simple answer you were seeking-but the truth is there isn't any simple answer.

I followed DynoDave's info, got a perfect clutch the first time. YMMV :mrgreen:

Thanks Dave!!

I'm with L.A.B. on this one.

mudplugger said:

without going into one of the forum marathon replies, please can somebody give me the correct stack height, clutch plate thickness. my bike is 1976 850cc elec start model. the lever has got heavier and heavier, I have taken the cable off, (seems to run ok) gearbox cover off to check the clutch body lock (it was suggested they can become loose) the plates are now removed for inspection. I am confident with spanners but it is great when you have been there before and this is my first time delving into the Norton engine or any bike engine for that matter. thanks Neil

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Neil,
L.A.B. is correct. What works for one bike may not work for another. I have a '75 MKIII and took these measurements and used Dave's target number when putting my clutch together

1) Bottom of basket to bottom of "C" clip groove 1.379"
2) Friction plates total thickness= .641"
3) Steel plates total thickness = .320"
4) Pressure plate= .227"
5) Have no info written down on spring (sorry)

Total of items 2-4 = 1.188" my target was 1.17"

I only had one set of steel plates but I did have an assortment of fiber plates to select from to get the height I needed.

This gave me a light clutch with no slippage at all. This also operates as Comnoz suggests spring should operate. Slightly concave at rest and flat when lever is pulled in. This may not work for you but it could be a starting point. Hope this helps.

Pete

many thanks, that all makes sense, I have read so much it gets confusing to understand, recently read that the length of cable is also critical. I will now start sorting and let you guys know the out come. cheers Neil

Neil,

I didn't read that you tried a new cable. If you haven't, that's the first thing to do. I never noticed the gradual change but my kid asked me how I was pulling the clutch. A new cable was a noticeable improvement.

On other bikes I've owned the cables just broke at some time. This one was probably original.

Jim

I used OldBrits method (as described by L.A.B.) to measure the gap between the diaphragm and the circlip and ordered (from RGM, but OldBrits can provide it too) an extra plain plate of the correct thickness so that the gap is as advised by OldBrits. What a difference! and the clutch is not slippering.

Laurent

Sequential steps for light lever vs tight clamping clutch
1. Adjust plate stack-up so the pressure spring is 4 to 5mm concave at rest (4 is lighter, 5 is tighter)
2. Fit and set pushrod endplay screw locked at 1/3 turn from pushrod contact
3. Fit and adjust lubed cable for 5+mm play at perch adjuster
4. That's all, folks.
Ta.

Gosh if I only knew what I was doing prior w/o measure by mix/match stack + pressure plate till spring just slips in groove against the stack but i must still be something wrong with this method as only takes 1/4 turn out of seat adj screw to work sweet easy sure for me. Likely just luck of the draw of manufacture variants and assembly on my 2 Combats so non mechanic slip shod fit works out for me.

where do I find dyno dave stuff. I have started checking things as above, and making some progress. need to find a bit more time :mrgreen:

mudplugger said:

where do I find dyno dave stuff. I have started checking things as above, and making some progress. need to find a bit more time :mrgreen:

Click to expand...

http://atlanticgreen.com/clutchpak.htm

http://atlanticgreen.com/norton.htm

Have fun
Pete

mudplugger said:

where do I find dyno dave stuff.

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The actual page "Easy Pull, No Drag, No Slip Commando Clutch" has been removed: http://atlanticgreen.com/ndnsclutch.htm

thanks for the info. My plate height is optimized because I added an extra steel plate many years ago.... Now I know why...

I've got an in-between stack height. The clutch isn't bad, but I think it could be better, but I can't find a plate that's thin enough to do it without the clutch slipping. I may try buying a fiber plate and see if it takes up the slop. My adjuster stud is very critical to proper clutch operation. It's always been this way.

As has been mentioned, a too tight primary chain will also make the clutch act strange and you really don't want the primary chain too tight, it's very bad on the sleeve bearings and the mainshaft in the GB as hobot will attest to.

here we go then. I have measured all plates and calculated thickness and heights, stack height 1.18" pressure plate .230" friction plate.125" 3 with sintered and 2 brass with oil way cut in plain plate .081 1 or 2 thou here and there. Measured with feeler gauge between spring plate and locking coil .023 I think I carried this out correctly, with plate flat ie turning, tried with tool removed it seemed less of gap. the only thing I struggled with was the 4 to 5 mm concave for light and no slip. I think I have about 2 mm, I put a straight edge across the basket and measured depth on vernier on the outer and inner parts of the spring plate. I have checked the position of the arm in the gear box, very slight adjustment. I will now get a new cable and set it up before putting all the covers back on. adjusted clutch as per above. do you all use gaskets still or use gasket silicon or similar. many thanks again, will bring up to date as and when. Cheers Neil

mudplugger said:

I have measured all plates and calculated thickness and heights, stack height 1.18"

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So, no apparent reduction in stack height (as standard according to the dynodave info is 1.172").

mudplugger said:

friction plate.125" 3 with sintered and 2 brass with oil way cut in

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Brass plates? :shock: Curious? Should be 5 identical sintered plates. :?

mudplugger said:

Measured with feeler gauge between spring plate and locking coil .023 I think I carried this out correctly, with plate flat ie turning,

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0.023" seems a reasonably good figure. I'm surprised your clutch is heavy, or, perhaps the stack height is not the main cause?

mudplugger said:

tried with tool removed it seemed less of gap.

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With the tool removed-there shouldn't be any gap?

mudplugger said:

the only thing I struggled with was the 4 to 5 mm concave for light and no slip.

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I'm not sure I understand where you're getting the "4 to 5 mm" figure from?

mudplugger said:

I have checked the position of the arm in the gear box, very slight adjustment.

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Maybe also check the lifter roller, sleeve and screw for wear, and the roller hasn't developed any flats?

Did you measure the total amount of clutch lift (at the spring centre) after adjustment?

mudplugger said:

do you all use gaskets still or use gasket silicon or similar.

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I can't speak for all but I use gaskets.

If the gasket you're talking about is the large O-ring, I silicone it into the inner case and put a smear of silicone on the O-ring just before I install the outer cover. Seems to work for me leak free.