Overpowering the Clutch no matter what.

StevenMain

New Member
Jul 18, 2016
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Texas
So I have been tweaking the engine im going to use on my scratch built suspension shifter bike build

Fully built China Doll reed valve motor I built, stuffed, ported, arrow kit, YZ85 Expansion chamber... I have had it now to 41.5 mph on a 44 Tooth !!! The thing screams and turns 10,000 RPMS.. but the clutch is slipping, I replaced the friction material, ruffed the crap out of the clutch plate, and cranked the **** out of the preload spring (the big spring in the case) No matter what I do the motor will overpower the clutch and it will start slipping. Any help ?
 

crassius

Well-Known Member
Sep 30, 2012
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how much grab the clutch has depends on the distance between the locked and unlocked positions of the hand lever - many of the longer levers do not have enough room there, so one needs to abandon free spinning at the lock position and just adjust for best grab (sometimes this can be fixed by filing down the frame of the lever to move where it stops when released so that it is farther from the handlebar)

another fix is to get a different lever
 

StevenMain

New Member
Jul 18, 2016
108
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Texas
There are 3 clutch adjustments preload, slack, and airgap which is typically incorrectly referred to as preload. The flower nut controls only airgap, which you want as tight as possible to the extent that the clutch is just barely dragging the motor idle rpm down a nearly imperceptible ammount when the clutch is in the locked lever position. Slack is in reference to cable slack you want just enough slack as to not be depressing the clutch arm when the clutch lever is released, But the moment you begin moving the lever the clutch arm starts depressing the main clutch spring. Clutch preload is adjusted on the big giant spring on the clutch shaft via the spanner nut... it controls the amount of pressure the clutch can squeeze the friction pads with.. This I have set very tight... the clutch lever is really stiff, if I adjust the spring any tighter, squeezing the clutch will simply coil bind the mainspring and not allow the clutch to disengage.

Adjusting the flower nut too tight to the point that there is no airgap and the clutch is still grabbing with the lever fully depressed does not make the clutch grab harder than proper adjustment. I did this just to humor a friend.

What I need is a stiffer replacement spring for the clutch main shaft like maybe a smallblock chevrolet valvespring. Or a better type of friction material. Like that of an automotive dry clutch. Does anyone else have experience with doing something like this?
 
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StevenMain

New Member
Jul 18, 2016
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Texas
It doesn't slip on takeoff ... it slips at around 25 mph when the motor starts hitting the powerband. Hits so hard it sounds like a downshifted. Either way I've adjusted all that can be adjusted, replaced the clutch main spring, and clutch pads, the clutch isn't glazed and looks great. All adjusted right, pressure plate good and roughed up. The clutch can't hold the power.. I'll have to source my own stronger clutch spring and a different clutch material and make my own pucks.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
156
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USA
never heard of such a thing with all parts aligned & seated, except when bottom of flower nut is hitting against outer lip of shaft - one fix is to trim off a bit of flower nut, other fix is to put pressure plate across vise, put large socket in center of plate, smack **** out of it with big hammer to get the dome of the plate a bit farther from shaft

see if that fixes it for you
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Los Angeles, CA.
Tighten the flower nut down as much as possible to where the clutch still works normally.


I've always had this problem with my race engines.

Some clutch shaft main springs aren't as strong as others, & you've already done all the sanding & cleaning the pads; so if there's still slipping?, try swapping out the main spring.
 
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StevenMain

New Member
Jul 18, 2016
108
4
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Texas
Just swapped main spring yesterday but until my new build goes together who knows if it will grip. If not I'm making semi metallic pucks.