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Narrow / Slim Transmission and Primary

1965 Views 2 Replies 2 Participants Last post by  KMetal
I am looking for the narrowest Transmission + Clutch + Primary possible.
I want to customise 1967 early shovelhead with 4 speed gearbox.
At the moment it has 3 inch belt, 3 stud clutch and Tech cycles 4 speed isolator series electric start kit.
But it is very wide and now I want to make it narrower/slimer.
What are my options? If you have any ideas (no matter how outlandish), please let me know!

My preferences would be: dry clutch, belt primary (1.5 to 2 inch), chain rear drive, electric start, removal of kick start. For driving, not for racing.

Apparently there is also a replacement mainshaft for 4 speed, that has splines on the end (instead of taper), so this would give me more options for different clutches. (I only found 2 stores on internet that has it, so if you have more information, let me know)
I was thinking to use 2002 sportster clutch, which is very slim. (both engines about 1200cc, similar power). I would have to modify clutch engagement, replace plates for dry ones, and lathe off chain sprockets and replace them with belt pulley. Not the best option, but doable.

Replacing a gearbox is also an option. If anything slimmer exists. Also possible from other brands, but it must take the power/torque.
I can get custom parts manufactured on lathe, mill,... to make it fit.

I am brainstorming at the moment, any ideas, advices, warnings, pictures, links, etc, are all welcome!!!

One inspiration is Christian Newman's stainless knucklehead (Win This: 1940 Stainless Steel Knucklehead Chopper). You can see how narrow his clutch is and also he remade kickstarter/clutch lever.

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Crankshaft sprocket must align with trans. sprocket, clutch outboard of that = barely measureable width difference. I don't see that the Knuck clutch in the photos is any narrower than my 1968 1 1/2" belt driven,5 stud clutch is. It's probably just me, but I think you are chasing something that isn't worthwhile.
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I measured on the motorcycle: Between crankcase and front belt sprocket is almost 2 inches of space. Then the sprocket is the same width as belt = 3 inches, and then from the belt to the end of the nut on the clutch is another 2 inches. If i squeeze front sprocket completely to the crankcase, leave 0.25" of space, it's 1.75" narrower. If I use 1.5" belt, I get another 1.5". If I manage to squeeze the clutch completely under the belt, I would gain another 2", but let's say I use 2002 sportster clutch: Total width of the clutch is 2.5", which means it would stick out of the belt for 1".
At the moment on the motorcycle the width measured from the Crankcase to the top of the nut of the clutch is: 2+3+2= 7 inch
My plan: 0.25 + 1.5+ 1= 3.75 inch.
That is almost half.
It would be even better to shave that inch off. So the width of the whole primary would be just the width of the belt, squeezed to the crankcase.
I understand, that moving the pulley (and belt), towards the crankcase, I will have to move transmission for the same amount (1.75") more to the right side. And then I would have to install a narrower rear wheel (Same as Newman did.) Otherwise rear chain would not fit.
And that will make a kickstarter stick out on the right side even more. That is why I want to remove it. Newman had reworked the kickstarter, but I just want to remove it, and keep electric starter. I need to find a replacement kicker cover, that has just the clutch mechanism or make it myself.
I would also consider replacing for right side drive transmission (So that I could keep current tires), but they are all 6 speed, so I doubt it would be any narrower.
The idea is that everything is only as wide (or narrower) as the engine crankcase. On both sides. Of course that is not possible, because it needs a primary drive, but as close I can get to that, the better.
This, at least, is the plan at the moment.

I am still looking for the splined shaft for 4 speed.
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