Wow, OK, the transmission floodgates have burst open! After endless jibberjabber on the elMoto, I’d had enough, I’m convinced that a transmission will work, and be a Good Thing, so I started this thread: “i can haz transmission?”.
Apparently, like bad habits, everybody has a transmission idea in their closet.
This thread is fast turning into an everything-you-ever-heard-or-wanted-to-know-about-buying-or-building-a-transmission thread. Some great ideas and resources.
For my part, I’ve decided that I’m modifying a stock Yamaha R5 or RD-series gearbox, and it’s actually a lot less daunting than it first sounded. Here’s how it looks with the cases split:
The plan is to remove the crankshaft and replace it with a simple drive jackshaft with a sprocket. That drives the clutch, so you’re using the stock motor hangers on the frame, the stock shifter, the stock clutch and clutch lever. The gearbox is completely sealed, apart from the crankcase, so it lubricates just as it would normally. You mount the motor on a bracket that bolts to the cylinder mounts, and drive the jackshaft through a slot in the mount.
Here’s the top of the case, showing the access into the crank:
The weight of the crank is considerable, and that’s getting lost, so it seems to me that this will be as light as is possible for a bike this size.
The jackshaft only has to go to the center journals, but I figure the bearings on all the journals should remain since they may contribute strength and rigidity, especially for that area of the cases, where you’re getting huge stresses.
Here’s a blueprint of a crank I found:
It looks like all I’ll need to actually have machined is the driveshaft.
Here’s one idea on the layout:
And the most dangerous part:
I have the complete lower end. it is hard to shift, I think one of the shift forks is bent or mis aligned. $80 for the whole lower end if you want it
From: Ted Dillard <firstname.lastname@example.org>
Sent: Tue, May 10, 2011 2:53 pm
Subject: parting out a 1972 yamaha R5 350
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I’m looking for a crankcase with clutch and transmission. I don’t need the top end.
Do you still have it?
…report coming soon!