Belt drive clutch issues

[Pompeydave]

Hi all, I've just recommissioned my turquoise DL125 with a Casa 185 kitted engine with a PWK 28mm carb, Kytronic programmed ignition box (brilliant piece of kit!), BGM big bore with ceramic coating, and belt drive. All is fine (a few minor carb adjustments still left to do) with one exception- The clutch is really 'grabby'. It's a standard new four plate effort apart from uprated springs, and it all fits into the belt drive crown wheel which is recessed to allow five and six plate clutches to be fitted if required.

It's no power monster, but has bags and bags of torque, so I've only gone for the stiffer springs. When I pull away in first it basically kangaroos until the clutch lever is fully let out and the drive is engaged. All the other three gears are fine. I did read somewhere on an old Scootering test that belt drive kits suffer from chatter and snatch at low revs due to doing away with the cush drive, but because it's such a torquey kit, I don't have this chatter. I just don't see how this could cause the snatchy release? I've had it apart and everything looks as it should so I'm stumped. It's really frustrating as it sooo smooth and quiet compared to the chain I had in there before. Vibration is almost gone so it's an absolute joy to ride apart from this 1st gear clutch release.

Is the standard four plate clutch too loose in the scooped out crown wheel? Doesn't look like it is to me. Any ideas anyone?

[rossclark]

I'd have thought it would be too tight if it's snatching.

Do all the plates and the pressure plate run smoothly in the crownwheel and spider? No burrs or notching on the plates at all ?

[coaster]

Provided that belt is adjusted correctly (up and down play) I'd be stripping the clutch to check for any uneven wear, warped or sticking plates. maybe check bronze bust while you are in there.

[Pompeydave]

All the internals are new. Anyone know if this crownwheel is designed for 5 or 6 plate clutches? Can't believe it wouldn't run properly with a standard 4 plate setup. I think I need to strip it again and check for parts catching on each other.

[Wack]

Looking at the pic although a bit hard to see but the rebates in the crown wheel look radiussed and I'm wondering if the bottom cork tangs are getting stuck ? Also if you've only got 4 plates in there, when the clutch is compressed there may be too much clearance which is making the plates snatch when released.

[Pompeydave]

Yep, a stripdown is the answer I think. It might well go better with one of the Readspeed 5 plate clutches.

[Warkton Tornado No.1]

It's no power monster, but has bags and bags of torque, so I've only gone for the stiffer springs.

It’s not ‘Horsepower’ but more actual torque that requires a better clutch to be utilised so I can’t understand your reasoning for using only four plates.

If the clutch components prove to be sound & engagement/disengagement is not being fouled by those radii in the sprocket catching the ears, then I’d be tempted to fit as many additional plates as can be added.

By now, I would have hoped you’ve stripped your engine to inspect the clutch components, but I wouldn’t be surprised to learn that eliminating the cush drive is detrimental to the transmission.

[Pompeydave]

Well I do think that a five or six plate clutch is the next step in diagnosing the issue. I'll change the plates accordingly and report back. I'll be disappointed if this is a non fixable problem as the bike is a joy to ride otherwise with almost no vibration now with the belt.

Actually, does anyone know if all two strokes with a chain drive between the crank and gearbox have a Cush drive?

[Warkton Tornado No.1]

Actually, does anyone know if all two strokes with a chain drive between the crank and gearbox have a Cush drive?

Many bike engines have a cush drive incorporated in the clutch in the form of rubber elements to absorb the shock regardless of chain or gear primary drive.

As far as I am aware, belts are not common in the primary drive.

Thinking laterally, in the case of auto scooter engines, you could ask the same question because I have no idea of whether there tends to be a cush incorporated as they use (non indexed) belt drive.

[Pompeydave]

Auto's have a centrifugal clutch and hence don't need a cush drive.

[Warkton Tornado No.1]

Auto's have a centrifugal clutch and hence don't need a cush drive.

I'm not splitting hairs @ all, but I imagine the inherant nature of a 'wedge' belt drive which is constantly slipping, even just a little bit, allows for the isolation of any NVH (Noise, Vibration, Harshness) so obviating any further requirement for a cush drive.

Theory versus Practical!

How is the actual analysis of the bike going? Have you unearthed any problems that may be an indication to what is causing the actual harshness?

[Pompeydave]

Been too busy to look at this again. Bought a hydraulic clutch conversion for it tonight on Ebay- should be interesting. Will fit a Readspeed 5 plate clutch at the same time and report back.

[coaster]

Bare in mind that the Reedspeed and other non-cassette type clutches all need to be set up carefully where tuned engines are concerned. You need to put it together and then compress it with a compressor and measure the gap between the plates. less than 1.5mm = drag, much more than 2mm = slip. Adjust the gap by using different thickness steels. This might even fix your existing clutch.

[Pompeydave]

Yep, thanks. All part of the fun of it I suppose, but every once in a while it would be good to fit something that works straight out of the box. No wonder R&D takes so long for manufacturers.