The Mongrel Clutch...
A little bit of the best of everything!
After racing the Box Stock class for years, I have never been fully satisfied with any clutch. Several have done a great job but each lacked something that the other had. What I wanted was an affordable multi-shoe drum clutch that "hit" right, had a nice stamped drum with machined friction surfaces, and used SMC/Bully style drive sprockets with needle bearings.
I have been most satisfied with the slip and lock-up features (how it "hits") of the MaxTorque Racing clutch, but the center hub was too soft for the needle bearings of the sprockets I wanted to use, so I had a hardened, two-piece hub made that would act as a good inner race for the needle bearings. I got a stamped steel drum that is a little deeper than other drums. The drum is made of thicker metal to allow critical surfaces to be machined so they are flat and square, minimizing run-out.
The problem with this clutch is that racers want to keep it a secret! If you have heard about the Mongrel, it is most likely because someone has seen it perform on the track and was impressed enough to figure out why. If it wasn't a superior combination, I wouldn't waste my time bringing all these pieces together. Now you understand why it is called "The Mongrel." It's a mutt, a Heinz 57...but it works, and it works like I want it to work.
The sprockets we supply with the clutch are made by Tomar, but the clutch has several internal spacers that can be removed as needed to accommodate similar gears. So use whatever sprockets you have, and add or remove shims to obtain the same amount of play the drum and sprocket has on the hub when the clutch is new out of the box.
The clutch comes with a spacer washer that is chamfered on the inside of one side. This spacer goes on the crank first and the chamfer goes toward the engine. The clutch can then be mounted either in-board or out-board using the supplied key and snugged-up with the included bolt and outside washer. DO NOT INSTALL SPACERS TO ALLOW THE CLUTCH TO SLIDE ON THE CRANKSHAFT. This will damage the hub requiring premature replacement. The clutch has plenty of play built in if you use the right amount of internal shims mentioned in the previous paragraph.
Keep the clutch clean. It is ok to spray the entire clutch lightly with WD-40. Lube the sprocket's needle bearings with a drop or two of gear lube after cleaning. Do not get Teflon anywhere near a drum clutch.
The clutch will stall or slip at 3100 RPM and lock up at about 3200 RPM. 3/4" bore x #35 chain.
Please note that it is not possible to use needle bearings with 12 and 13 tooth gears. They have bronze bushings.