A65 KTM Clutch

[DMadigan]

In case anyone is interested, made a new clutch using KTM parts. Eight plates with Belleville spring. All the parts are KTM except the chainwheel, drum and hub.

Made one for a B50 racer. It lasted the whole weekend of racing where the stock clutch would start slipping in one race.
The Belleville spring has three tension settings and goes over the knee in the deflection curve so the pull is lighter at full lift. The chainwheel runs on a double row ball bearing so it does not flop about when the pressure plate is lifted. Not shown is the ball thrust bearing in the pressure plate.
The inner bits:

[idie]

Very well done.

[EDDIE SIMPSON]

a better set up than a belt drive conversion in my opinion. a diaphram clutch like the norton commando, which will not fit the a65 i believe. [ i googled ]
Question is, how much?
Will the standard pushrod mechanism be strong enough for a diaphram clutch?

[DMadigan]

Actually, the Norton Diaphram clutch does fit (although this is on a T120)

I have not got a price together yet. I have to find out what the shop cost will be. I just make the prototype, they are faster at producing my parts. I also have to decide if there is enough interest.
The KTM diaphram spring has three settings by changing the position of the retaining ring. It goes over centre of the K curve so the lever force goes down at full travel like the Norton.
My intent is just to provide the non-KTM parts since the KTM parts are readily available and no point in me stocking parts and having to add cost to those parts.
At the moment I am making a belt drive chainwheel for it to go in my A65 case/Yamaha crank/Honda rod/90 degree/three bearing mains engine.

[EDDIE SIMPSON]

hi dave,
i thought someone would have asked the obvious question by now of why not use a Norton diaphram clutch? As you stated, it fits the a65 .Parts are priced reasonably and available. is the KTM clutch that much better?

[DAVE BRADY]

Hi,

Isn't the Norton clutch very heavy?
I have seen photos of the  "A65 case/Yamaha crank/Honda rod/90 degree/three bearing mains engine" and it looks amazing.  It just shows what can be done and perhaps what BSA should have done.

Dave.

[EDDIE SIMPSON]

did you solve your clutch problem Dave? i seem to remember you were asking about the 7 plate clutch upgrade.

[DMadigan]

A problem with the Norton clutch is there is no damper. Norton put the damper in the rear sprocket carrier. That bike has a rear wheel damper so I could use it there. That one has an aluminum basket, not steel so a bit lighter.
I would not bother with a 7 plate upgrade because it still has the basic problems of the stock clutch.

[DAVE BRADY]

Hi,

I am using the early 4 spring clutch and ended up removing the lip at the rear of the clutch.  This made it more like the 3 spring and meant I could fit an extra plate.  It is working OK so far.
The 4 spring worked well with the long stroke 750, two up and with a trailer. With what I have done, it should be as good but hopefully a bit better.
On my other A65 I have a bit of a modification to help reduce any wobble. I did not come up with this myself but I know it was used for quite a lot miles in another bike.

[EDDIE SIMPSON]

i m also using the 4 spring clutch on my a65 and it feels and looks firmer than the 3 spring affair. the 3 ball ramp mech doesn t allow for much lift movement.
i suppose the Norton commando was a bodge up to the mark 3, without a cush transmission drive. Maybe a commando clutch and a cush sprocket is the way to go. i ve seen a cush sprocket used on retro racing triumph triples.
The modern jap clutches have a coil spring on the drive ring which is too wide for a bsa .
i have a pearson suzuki clutch in my garage but it has no transmission shock absorber either.
So i would be interested to know how the KTM clutch overcomes the transmission shocks.

[DMadigan]

The KTM clutch has a damper in the hub.

It is possible to put a damper in the engine sprocket. I am making one for a BNR belt drive clutch which has no damper. Reports are it causes rear chain problems.
With the Norton damper in the rear wheel, the gearbox is still getting the impulses from the engine that a clutch damper would not transmit.
Kawasaki typically uses springs between the drive gear and clutch basket. Yamaha has used round urethane cushions.

[Allan G]

Hi,

I am using the early 4 spring clutch and ended up removing the lip at the rear of the clutch.  This made it more like the 3 spring and meant I could fit an extra plate.  It is working OK so far.
The 4 spring worked well with the long stroke 750, two up and with a trailer. With what I have done, it should be as good but hopefully a bit better.
On my other A65 I have a bit of a modification to help reduce any wobble. I did not come up with this myself but I know it was used for quite a lot miles in another bike.

The 4 spring unit works well, Mark Parker is using one on his 883 A65, this bike is highly tuned and he has no issues.

It helps because the basket and the hub centre are sandwiched toghter.

The 3 spring fails for several reasons, Incorrectly sized rollers (a ball bearing would be far better for controlling wobble), and most importantly is the wear between the endplates, the 3 legged web (which wears the plates - and itself) and the cush drive rubbers. You also have the likely hood of chain misalignment. Another thing to note is when I was fortunate to chat with Les Mason, he was telling me that he raised the issue with the factory (when he worked at BSA), the primary ratio on the Triumph T120 was slightly taller at 29:58, whilst it is 28:58 on the A65, adding more load to the clutch.

To install the rubbers, you need to sacrafice a centre hub (the tapered section) or a mainshaft to sit your hub on. and weld a bar to a plain clutch plate. then you can drop the larger rubbers in first (which will have more crushable area than dropping in the smaller rubbers) then place those rubbers under tension before you drop the small rubbers in...

By the time you have bought new rubbers, 3 legged web (or spider as some call it) and end plates (or had your end plates surface ground to remove the wear out of them, making them flat again) your into the price of buying new a clutch cush drive.... either way the rubbers are rubbish and not suitable for most oils. If someone made urethane cushions like on Dave Madigans KTM clutch then the Beezer/Triumph clutch would be a lot better and likely not wear as the same rate.

Dave Madigans clutch/basket looks to be a much better solution. My experience with the BNR clutch having the similar style of pins for the plain plates instead of slots has proven not to wear, unlike the slots.