Cluttch issues

[JayLael]

The clearance measurement of the "gap" is between the iron inner hub part and the outer aluminum cover of the clutch it's self. My experience has shown if you get too many plates crammed into the assembly ie too thick of a clutch pack, that gap gets down too small, so once it's assembled, you try to pull in the clutch lever, but have a rock hard clutch lever pull, that won't pull in all the way, potentially breaking the actual outer clutch cover where the pusher cam thing is, and it just won't work. When I assemble them with this gap, at say 6 or 7 mm, (any larger than the least I can get away with) It only takes a short time of abusive expert level motocross type riding, (ahem) and the clutch begins to slip, a small amount at first, then it gets worse quickly.
Any horsepower lost via a clutch slip, however small, will use up precious horsepower, that we just can't waste. As for adjustment via shims, I just try the cover, and wiggle the lever until I have a good 6-8 mm of freeplay at the lever down below. This give us room to adjust the cable slack to allow for clutch plate wear. To give you an idea, at the last race I had to take out one of those shims, between motos, and I had started moto one with a fresh clutch, and about 6 mm of free play in the lower lever. By end of moto one it was zero. I also run the upper clutch lever freeplay at about 13 mm of rattling slack. This allows the clutch to bite closer to the lever when letting it out. I have big hands, so I had gotten in the habit of having it take hold out near the end. I was getting beat off the starts, so with it adjusted this new way, I get much better starts, even a holeshot or two this year.

Kevin, I had run each of these at different times. I am finding the 4 plate model 94 wombat clutch, does allow the engine to rev quicker. Problem is it seems to slip sooner, or slide into engagement, which eats up precious horsepower. I can't seem to pack one tight enough to get really good performance, but I intend to try and fit a third set of springs, maybe the littlest ones from the early 100s will fit inside the smallest Wombat spring. I haven't tried it yet. If not that then I may try adding flat washers under the springs in the spring pockets.
The five plate clutch I am using now is fantastic. It has really decent clutch pull, not over hard like some Triumph dirt track bike, and still doesn't slip drag chatter or slide into engagement. With that, my Wolverine can hang with any 125 I've raced with anywhere.

[JayLael]

I suppose it should be said that we are not using any of those old all fiber plates, only the new type friction discs from Paul at Strictly Hodaka.

[Bruce Young]

The clearance measurement of the "gap" is between the iron inner hub part and the outer aluminum cover of the clutch it's self. My experience has shown if you get too many plates crammed into the assembly ie too thick of a clutch pack, that gap gets down too small, so once it's assembled, you try to pull in the clutch lever, but have a rock hard clutch lever pull, that won't pull in all the way, potentially breaking the actual outer clutch cover where the pusher cam thing is, and it just won't work. When I assemble them with this gap, at say 6 or 7 mm, (any larger than the least I can get away with) It only takes a short time of abusive expert level motocross type riding, (ahem) and the clutch begins to slip, a small amount at first, then it gets worse quickly.
Any horsepower lost via a clutch slip, however small, will use up precious horsepower, that we just can't waste. As for adjustment via shims, I just try the cover, and wiggle the lever until I have a good 6-8 mm of freeplay at the lever down below. This give us room to adjust the cable slack to allow for clutch plate wear. To give you an idea, at the last race I had to take out one of those shims, between motos, and I had started moto one with a fresh clutch, and about 6 mm of free play in the lower lever. By end of moto one it was zero. I also run the upper clutch lever freeplay at about 13 mm of rattling slack. This allows the clutch to bite closer to the lever when letting it out. I have big hands, so I had gotten in the habit of having it take hold out near the end. I was getting beat off the starts, so with it adjusted this new way, I get much better starts, even a holeshot or two this year. Jay, if you don,t have any of those little 100 springs call me I will send you some--no charge. . 1--208--571--2823, have you thought of trying a more modern spring from another brand of big, that is the same size as hodaka, but modern spring materials and less slag. Just a thought. Bruce Young Hodakaparts.com IDAHO

Kevin, I had run each of these at different times. I am finding the 4 plate model 94 wombat clutch, does allow the engine to rev quicker. Problem is it seems to slip sooner, or slide into engagement, which eats up precious horsepower. I can't seem to pack one tight enough to get really good performance, but I intend to try and fit a third set of springs, maybe the littlest ones from the early 100s will fit inside the smallest Wombat spring. I haven't tried it yet. If not that then I may try adding flat washers under the springs in the spring pockets.
The five plate clutch I am using now is fantastic. It has really decent clutch pull, not over hard like some Triumph dirt track bike, and still doesn't slip drag chatter or slide into engagement. With that, my Wolverine can hang with any 125 I've raced with anywhere.

[JayLael]

Thanks Bruce: I have a bag full, just too busy to try it yet. It's on my work bench now.

[thirdstone]

Jay those springs have been a long term puzzle for me . I really think that they should be replaced with one stronger spring. That you are thinking of adding another smaller spring sort of confirms this thought. There must be clutch springs out there that will do the job. The issues you have with the clutch just go to show that for high output engines it's the next weak link. Short of next level KX80 clutch a La Lee Fabry we need to pursue this further.

Kev

[Zyx]

Multiple springs are used to achieve a target rating while still having enough free length in the spring. Commonly, a single heavier spring will achieve its rating by using thicker wire, which limits free length. It's possible, but problematic. Even modern hot rodders will use multiple springs on a high lift cam to reach a spring rating that works but still allows needed length of compression without binding.

What might work here is to find a spring winder like Paul did for the control rod springs who can spin up some high tech clutch pack springs that have a higher rating.

One thing I have noticed about clutch springs is that there is almost never two with the same length. They may fall within a short range, but consistency is out the window. Can't tell if it is because they are used, or because of manufacturing tolerance, or what, but I usually sort through what I have to make pairs with similar tolerance differences, then color code them so I can tell them apart. Better still would be to have a spring scale and sort by strength instead of length, but I don't have one of those. I suppose I could make one.

[thirdstone]

Ok I'm still a bit puzzled by how this clutch works. Am I correct in saying that slippage is a function of spring pressure ? Would stiffer springs reduce clutch slipping on high HP engines? Would shimming the springs to increase preload help ?

[bchappy]

I remember we added a small flat washer under each spring on our flat tracker made from an Ace 100 about 1969 and it stopped the slippage. That was before the time of the spring inside the spring. It was just what we had to work with at the time. So from my experience it will work.

[Zyx]

Is slippage a function of spring pressure? Yes. However, spring pressure is comprised of the condition and length of the springs, AND by the build height of the clutch pack. Consider what would happen if you just took out one friction disc. It will work. It will feel lighter than before. And it will slip when pushed. This is in good part why Jay suggested that the gap on the clutch cover should fall within a range. Too wide, too loose and it will slip. Too small, too tight and it will perhaps not release all the way.

You have a very strong motor now, but still have a stock clutch intended to work with a modest output. Without changing to an entirely different clutch (and choices are few) you have to improve the function of what you have. New style friction discs, and all the clutch mods and tuning described above, about all there is. Engine oil may be a factor depending on what you are using.

Adding shims under the springs will slightly raise spring rating, but be certain that when you do that, you do not compress the springs to the point of binding. Slightly stretching the springs will do the same thing as shimming, but exercising springs this way shortens life. I would rather use a stronger spring, if you can find one, than shimming the ones you have. Or see if adding one steel disc leaves you still within the gap range described above. Adding a disc also compresses the springs same as adding a washer. But the springs are only going to give you so much. They can't be made to do a whole lot more than their design intended.

How many steels and friction discs do you have in your clutch, and which engine did the clutch start life in?

[thirdstone]

Stock 4 plate 94 clutch with new SH plates
I guess an extra steel has the same effect on the spring as a shim .

[Zyx]

As nearly as I can tell from the schematics, you can turn that clutch into a 9 disc clutch (5+4) by swapping out the cage. Strictly Hodaka has them for just under $100 US, or perhaps someone has a god one to spare. I think you would be ahead by working with the larger clutch to start with rather than making the smaller clutch work harder.

So if I followed the tech discussion, you might get one more steel into either clutch of the stack height is within limits.

[JayLael]

The latest info I have come up with is that,
The 6mm flat washers placed under the clutch springs improve the holding power and provide a more positive feel. I have done this to the model 94 and the model 95 clutches to great effect.
The Ace 90 (smaller diameter) springs will not fit inside the smallest Model 94 95 etc spring.

The 3mm spec for clearance in the port hole is minimum. If it's less than that it won't release properly. Once the clutch is fried the clearance will become about 6 mm. Check this with metric allen wrench.

The part I refer to as the center star piece, the one that engages the inner teeth on the friction plates, (run to your book and tell me what it's really called if you must) seems to explode once every three and a half motos or so. Your results may vary. I have a sack full on hand and investigate the clutch every three motos and usually find something is broken, usually that center star thingy.

The clutch I am using now really puts the power to the ground like never before, on the souped up 125s. The model 94 clutch seems to give quicker throttle response and more power by virtue of it's lighter weight. It won't last long without the washers however, even at three mm of clarence.
That's it for now.

[taber hodaka]

Jay
Three mm of Clarence should hardly be sufficient.----------Clarence

[thirdstone]

G`day Jay, its the clutch rotor gear..and stop using them all up !!!!!
There must be a way to get through a meeting without pulling the clutch off , not that it takes long to do .

[JayLael]

Jay
Three mm of Clarence should hardly be sufficient.----------Clarence

I was hoping you'd catch that!
The clutch rotor gear does sound more official than star gear thingy. Ha ha Hope all are having a great day!

[Zyx]

I like star gear thingy. Much more descriptive. If military inventory, it would be thingy, star gear, one each.

[thirdstone]

Looking at my clutch hub gears I notice one with larger holes, it's 25g lighter.
Is this a stock hub or has someone enlarged the holes?
Thanks

[bchappy]

Don't know for sure but think someone did this. I would think that the reduced friction area would offset the weight difference.

Edited 9/23/15: Disregard my comments. Obviously from the next few comments I don't know what I am talking about.

[Zyx]

Looking at the friction discs, it is not clear that the holes overlap the swept area. If not, this would have no effect on friction surface.

[BrianZ]

I'm pretty sure the clutch hub with the larger holes is stock, as I have seen several of these in my experience. My guess would be that the larger holes were to reduce weight and allow more oil movement in the clutch.

Brian

[Bullfrog]

I too think the larger holes in the clutch hub are stock . . . though I can't tell you when that started.

Jumping back to a previous post . . . Jay, any chance you could post a photo of an exploded rotor gear? I haven't seen one in that condition. I'd like to see what the forces do to it.

Ed

[admin]

Toad's Captain. late 1974

[JayLael]

Ed, I will work on that, or just mail you the pieces. I'm at work today and the pieces are at home.

I am kind of excited to share what may have been obvious to those of you with intuitive thinking, but I just now figured out!

Simply assemble the clutch cage and the aluminum cover, then slip the clutch hub down into it until it bottoms out. Then measure the depth as best you can. On a wide 95, (up) clutch, I measured 18.5 mm. Then subtract 3, and you have the approximate stack height you want. Then simply shuffle the plates and try different combinations until your clutch pack thickness is somewhere close. They seem to measure less when assembled than when just measured loose. Mine ended up at 15.8 mm, when measured loose, and has a window measurement just over 3 mm.
This saves repeatedly assembling the unit to measure clearance at the port hole. Eureka!!
This particular clutch pack has one of the thick frictions made from two single sided frictions, and three paired steels, as paired steels are less likely to break than when single, (they are all relieved to clear clutch bolts) and the steel thicknesses vary too, so there are enough wild card factors that mixing the parts around is how youu get the right pack thickness. In this particular wide clutch, the friction count is not 5 but four, which makes room for the paired steels and allows for selecting various combinations of discs. The friction plate failures I have had are usually just the one disc nearest the hub, wears off one side. This clutch uses washers under each spring, and clearance came out slightly over three mm.
I have to back pedal on my statement about using loctite on the nuts where the saftey wire was before. The loctite caused buggered threads on the cover and screws when I took the clutch apart again. I assume that's why nylock nuts are the norm. Also if you grind the screws off flush with the nuts, the next time you take it apart, dress the ends of the screws with a file so they don't damage the aluminum cover's threaded holes, as these little guys are getting more rare and expensive. I have a machinisht friend who is going to modify some of the early smaller spring pockets to the larger model 95 up size. Then the vast pile of 100 covers will become useable. I also have been drilling them out with the vent holes to match the later ones like on Super Combat etc.

[JayLael]

Here are the remnants of the clutch rotor gear after two motos at Washougal. I should note that the pinion gear on the crankshaft was replaced with one that fit nice and tight on the clutch rotor gear.

[thirdstone]

Hi Jay just a couple of questions.That rotor looks quite blue inside so I have to ask what probably is a redundant question, did you have the thrust washer fitted? Another question , if you are using locknuts why do you need threaded holes in the plate?
I'm working on a clutch hub mod to allow other bike clutch springs to be used.
All the best ..Kev