Slipping clutch?

[cdsdorset]

One of my pals was plagued with a clutch slipping issue last season - and after multiple strip downs and much fettling it came down to being due to the oil he was using in the primary drive. Not the plates, spring tension etc etc.  I think he had heard somewhere to use some modern fancy oil - and this was the cause of his trouble. (Next time I see him I'll ask him for further details...)

It's quite possibly the oil.I was using the same stuff in the primary chain case that I used in the engine,(10/40 semi synthetic)Now having stripped the clutch I will replace the friction plates,and when the inserts I ordered for the chain wheel arrive,if they look ok I may order inserts for all the friction plates.It will be about half the price of new friction plates

That will be your problem. Only ever use mineral engine oil or ATF trans fluid in the primary. ATF not AQF!

[Derek996]

...It's quite possibly the oil.I was using the same stuff in the primary chain case that I used in the engine,(10/40 semi synthetic)...

Be wary of using modern oils in an old engine. These engines have no real oil filter and over time deposits will gather in nooks and crannies within the engine and probably even more so in the bottom of the oil tank. Modern oils have detergents that will loosen off all these accumulated deposits which will then be distributed around the engine and can cause damage to bearing surfaces. Unless the engine was been stripped and the internals thoroughly cleaned, also the oil tank, then detergent oils are best avoided.

[neil1964]

Personally I would only ever use Surflex friction plates. Having had 6-spring niggles in the past I rebuilt my clutch with new double row bearings, new plates, new (genuine NOS springs) with a 5-plate basket (Gold Star scrambler). I used new nylon lined cable and new pivot. The clutch is perfect. Light, no slip, no drag always find neutral even when hot. I actually do use modern Castrol 10/40 as used in bikes that share clutch/engine and gearbox oil (GP50 in engine).
If I could only get my NEB in the 600 to work as well without dragging!!

[Janacek]

Personally I would only ever use Surflex friction plates. Having had 6-spring niggles in the past I rebuilt my clutch with new double row bearings, new plates, new (genuine NOS springs) with a 5-plate basket (Gold Star scrambler). I used new nylon lined cable and new pivot. The clutch is perfect. Light, no slip, no drag always find neutral even when hot. I actually do use modern Castrol 10/40 as used in bikes that share clutch/engine and gearbox oil (GP50 in engine).
If I could only get my NEB in the 600 to work as well without dragging!!

Looked up Sureflex friction plates,and the price! Almost twice the price of unbranded ones.Having fitted many pattern parts I have not been impressed with the quality and fit of most so I suppose I will have to open my tight Yorkshire wallet and buy decent quality.

[Janacek]

...It's quite possibly the oil.I was using the same stuff in the primary chain case that I used in the engine,(10/40 semi synthetic)...

Be wary of using modern oils in an old engine. These engines have no real oil filter and over time deposits will gather in nooks and crannies within the engine and probably even more so in the bottom of the oil tank. Modern oils have detergents that will loosen off all these accumulated deposits which will then be distributed around the engine and can cause damage to bearing surfaces. Unless the engine was been stripped and the internals thoroughly cleaned, also the oil tank, then detergent oils are best avoided.

Thanks for that Derek.I used to have a canal boat and the same reasoning for using modern oils was put forward.Although most newer boats favour Japanese diesels there are many older ones using Lister,Perkins and BMC diesels.Mine was BMC and used any modern 20/50 oil.I did change oil every 50 hours and had no trouble.Others used Morrisons Classic 20/50 or Halfords classic oil.
Thinking of what you posted,I will use Halfords or Morrisons in the bike.

[neil1964]

There are different numbers of plates and depths of baskets.  The B31 having 3 friction plates and the Gold Star 6.
If your basket will allow maybe go for 4 friction plates (you may need longer springs). Dragnfly have a good page with the various types of

[Janacek]

I have priced up replacing my six spring clutch with the later four spring one;more than £385 from Draganfly.
The problem I have with my six spring clutch is the friction inserts for the chain wheel are unavailable.
Rather than stump up £385 I will make my own chain wheel inserts.
Quite difficult finding material thick enough (8mm) but I found a couple of suppliers.
Question is;there seems to be three types, natural cork,nitrile bonded cork and nitrile neoprene rubber bonded cork.
Which to use? anyone know?

[Derek996]

This is what an AI response says:

AI Mode conversation: Which is the best motorcycle clutch insert material, natural cork, nitrile bonded cork or nitrile neoprene rubber bonded cork?

Nitrile neoprene rubber bonded cork is widely considered the best choice among the three for motorcycle clutch inserts, particularly for vintage restorations or custom relining.

You can read the whole answer here.

[limeyrob]

I used plain cork in the past, but some used to be woven, perhaps asbestos? So its worth being careful with old stock in case its very old.  I suspect eh asbestos were the best of the lot.
Make a jig as pressing them in all the same amount is tricky.
I suspect the whole problem is caused by the oil This is not a "wet clutch" in the true sense as its not submerged, its a dry clutch that gets oily.  I don't have the B31 torque curve to hand, but I suspect the sip is at peak torque which would make sense.
I would expect the "original" oil to be SAE 30 filled to just below the clutch basket.  Now ATF is a good option as its designed to lubricate gears but also allow the brake friction bands to grip.

[Janacek]

More clutch woes!  1957 B31 six spring clutch.
Replaced clutch springs,cleaned clutch plates and road tested. No slipping! However the clutch action is now very stiff and "notchy"I think the cable needs replacing as the plastic outer cover is broken in a few places.
Replacement clutch cables seem to be 2mm inner,but the one on my bike is 3mm,with a 5mm outer.This is 5mm metal outer where the plastic has broken off.
What is the correct diameter inner clutch cable supposed to be?
Looked at a Venhill clutch cable replacement kit and their inner is listed as 2mm.

[Derek996]

... However the clutch action is now very stiff and "notchy"...

Have the plates worn grooves in the clutch basket?

What is the correct diameter inner clutch cable supposed to be?
Looked at a Venhill clutch cable replacement kit and their inner is listed as 2mm.

I don't know what it should be. Mine is 2mm but I made up the cable myself.