Ball and ramp clutch?

[1974jh5]

I think about 90% of the stock clutch mechanism's problems (hard to pull, fussy to adjust, loses plate travel when hot) can be traced to the worm gear. When it gets worn, the friction increases and also the travel decreases because it cocks sideways etc. Redrilling the hole in the worm drive lever helps with travel but doesn't help with friction.

It seems Harley big twins, Viragos and a fair number of Hondas use a 'ball and ramp' release design which would get rid of some of these problems. Anyone tried this?

The Harley version:

I bought one as an experiment since they were cheap, unfortunately it's too big to fit without cutting the outside case.

Virago version:

The parts needed total about $95.00 new so I wasn't nuts about experimenting with that. Anyone have a Virago with a bad motor they'd be willing to sell parts off of?

 

[TeeCat]

I have never heard of that before, but it seems really ingenious if you think of it, especially because it would address the friction issue.

Do you mean cutting the case itself, or the case cover? I'm trying to envision how that would work.

TC

 

[1974jh5]

The Harley version is about 3/8" too big in OD. That means the mag case (not the main engine case) would have to be slotted and it would be extremely close to the mag rotor, there probably would not be enough room to weld/epoxy a piece in to seal the case and i wouldn't want chain lube flinging in there. It might clear a PMA but I don't know for sure. The mechanism would need to be somewhere around 1 1/2" to 1 5/8" OD (might be able to squeak a 1 3/4" in) to clear the case.

You can see the vertical 'rib' in the case which seals the mag rotor in this pic. I'd like to not have to cut that if at all possible. It meets with a similar rib on the main case which I definitely do not want to cut.

 

[1974jh5]

I found a Virago setup on fleaBay for $15.98 including shipping so I am gonna roll the dice.

 

[5twins]

You might have difficulty making that work. The Virago lever is on the outside of the case, under a little cover, not inside the case like the 650.

 

[1974jh5]

Right, I saw that. Here's my rough plan, and please keep in mind all dimensions are very approximate: the flat plate will go on the case. The back of that plate will have two holes drilled so that set screws in the stock worm screw race screw locations will keep it centered and prevent it turning. That part already has 1 hole for a dowel pin so it's the same way Yamaha did it. The part with the adjuster screw (Yamaha calls it a 'push screw) will have 3 holes drilled/tapped on the back side, then I will fab up a lever from some flat steel and bolt it there, thus moving the lever inside, and use the stock XS cable adapter clevis on that. I will drill two holes in the lever, one in the stock position (1 5/8" from center to center) and one inward about 3/16" so I can test two different linkage ratios. I need to figure out a way to keep it from falling apart during installation, I think I can do that with a spring and a circlip and a machined groove but we will see.

But there is also a saying: 'no plan survives first contact with the enemy.'

Virago parts:

The top piece is the 'push screw', the round flat one is the race which goes against the case and the triangular piece is the race which holds the balls (duh).

 

[5twins]

Notice how the ball indents on both parts are "ramped". It's designed to turn in the opposite direction than the 650 does.

 

[1974jh5]

I looked at that. If the flat race (the piece in the bottom right of the picture) is on the case and remains stationary, then the indents ramp 'up' to the right meaning the rotation is clockwise to expand it, same as the XS goes clockwise to wind the screw out of the holder. If it were the other way, i.e. the part with the adjuster screw was stationary then yes it would operate backwards. The 'ramps' on the screw piece have to point the other way from the flat race for it to work properly, otherwise when you tried to turn either piece it would just sit there, or be very hard for the ball to 'climb' out of its resting hole. The Virago parts pic shows the lever facing to the right as viewed from the outside of the case, meaning to me it's supposed to go clockwise.

The way I plan to use it is so that the adjuster screw will stick out of the case in the same spot as the stock worm gear setup. If all goes well, from the outside it will look 100% stock including the cable. I am a bit curious about the adjuster screw, I may have to modify the Virago piece to work with the XS 650 ball or go to a 1 piece clutch pushrod.

About the pushrod: it wouldn't surprise me to find that the stock pushrod flexes. There are companies such as Manley who will make a chrome moly pushrod to any length you want. Maybe...

The Harley setup can go either direction but unfortunately is too big.

 

[dwyatt]

This could be a nice option, thanks for working out the details and sharing. I'm running a hydraulic set-up, which works great, but if I try to take my bike to an AHRMA race, I have to go back to a mechanical set-up and wasn't hot on the original, but this would work.

 

[1974jh5]

I'd like to do a hydraulic, but it either requires the slave be mounted outside the case like the Aprilia setup if you want a direct action self adjust, or with a slave cylinder and cable like Hugh's. That looks like a great setup, it is on a zillion dirt bikes and and it's certainly priced right but it doesn't address the worm screw wear issue and it still requires periodic adjustment.

I suppose I could figure out a way to put a slave cylinder inside the case (I know it's been done before) but this just seemed like something to experiment with even though it's not self adjusting.

Who knows; if I can get it to work nicely I may ditch the whole hydraulic idea entirely.

 

[retiredgentleman]

The main problem with the stock clutch arrangement is that the stroke of the pushrod (plate separation) is not large enough. The stock set-up gives about 0.079" of plate separation. I drilled a second hole in my actuator arm which now gives about 0.097" of plate separation. My clutch works better.

I found the stock lever pull to be light. The mod I did does make the lever somewhat harder to pull but not excessively so.

I don't really see the benefit to HHB design. All it does is replace the cable with a hydraulic hose................you still have the mechanical worm gear. The clutch is still mechanically operated, so its not a hydraulic clutch.

 

[1974jh5]

I'm using heavier than stock springs, that probably has a lot to do with it. I redrilled my stock lever like yours, but it got to the point after about 30 minutes in traffic that it was a remarkable PITA. Lubing the dickens out of everything helped but did not fully fix it. The metal tube at the bottom end of the clutch cable doesn't help anything, I am sure; my XR400's stock cable was like that and the Motion Pro replacement didn't have the tube, the effort was noticeably easier. I have been tempted to see if I can make a cable without that tube for mine. That is a big thing in the dirt bike world, fanning the clutch will wear you out quick if the effort is too hard and for that reason off road riders have gone after easier clutch action for years.

The Hugh's kit gets rid of the cable friction and does self adjust, to a point. In those respects it's better than the stock deal for sure. It would probably work okay if the hole in the lever was redrilled like retiredgentleman's.

 

[1974jh5]

Well, got the parts and was able to install them. It wasn't difficult, there was some grinding and welding involved but nothing ridiculous. Unfortunately, the clutch pull is actually harder than with the worm screw setup, that is probably due to the ball ramp angle. I did make some measurements with a dial indicator; the stock setup travels approximately .062" with the hole moved in like retiredgentleman did his and the Virago stuff was good for about .820" using the longer lever that came with it. So there is still a possibility that the lever can be lengthened or the ball ramps ground to put the travel in a sweet spot of around .070", but that's a project for another rainy day.

 

[5twins]

I think increased travel and plate separation should be one of your goals. I feel that's one of the major short comings of this clutch - the plates barely separate enough. When things heat up and you lose travel, the plates start to drag. Then you get the harder shifting and next to impossible to find neutral at a stop.

Because the lever pull is so stiff on these bikes, I switched to a Kawasaki lever and perch assembly because the lever pivot is nearly 4 times as wide. Hopefully I'll never wear this one out, lol .....

 

[mrkil]

what model is that lever from? it's a great idea

 

[ippytattoo]

That looks like one I have from a KZ900. I am no longer using it as I went to an Aprilia Hydraulic clutch.

 

[5twins]

KZ440, I think it was used on some others as well like the 550. I just bought a complete assembly off eBay to have as a spare for about $15 .....

http://www.ebay.com/itm/27096238603...34&viewitem=&sspagename=STRK:MEWNX:IT&vxp=mtr