The 100% Biker Project Bike.
Part The Fourth.

Right, next problem to solve is the drive set up. We've opted for a chain drive for the bike, but right now I have a rear wheel with an FJ1200 sprocket and a GS750 mainshaft on the engine. Plus the rear wheel is so wide the sprockets are well out of line. After considerable head sctratching its back ovet to B&I for a custom offset front sprocket.

	First off I've been out and bought a front sprocket for an FJ12. This means that the chain pitch will match, and final gearing should be in the right ballpark. Tony's machined the centre out of it on the lathe. Next he turns off a shoulder onto the end of a piece of mild steel bar and fits the sprocket onto it before welding it in place.
	The next step is to machine out the bar until we end up with the new spocket mounted on the end of a section of tubing. The inside diameter of the tube is determined by the socket I'll need to get inside it to fasten up the sprocket retaining nut onto the output shaft.
	Turned off to length now, and the next step is to carefully turn the teeth off the old GS750 sprocket so we're just left with the slined centre. Tony can now weld this onto the end of the tubing. This all needs to be done on a lathe to keep it concentric, and carefully measured to give the correct offset for the chain.
	Sprockets should ideally be case hardened, but in out case we'll have to settle for tempering the old fashioned way. Tony heats up the new sprocket to cherry red before plunging it in water to harden it.
	And here's the finished item. It's a big and heavy lump and ideally I'd like to have extended the output shaft and fitted an outrigger bearing, but with the chain set upcorrectly it should give us a result.

Back in the Shed of Destiny and up on the workbench, I now need to start finding solutions to some of the problems of where to mount everything. I've a batter to accomodate somewhere to say nothing off all the electrical gubbins I'm going to have to bolt on later. Before leaving B&I Engineering I subtly purloin one of Tony's cylindrical oil tanks he makes for Harleys, which is just the right size to go in the middle of the frame.

	Its an easy but surprisingly time consuming job to chop a big square hole out of the top of the oil tank to accept the battery. careful work with a file gets it just right, eventually.
	And then I can weld a couple of tabs to the frame to bolt up the oil tank. Lined up carefully this means I can drop the battery in from above, so it shoulb be more or less invisible with the seat on.

And that's it for another update. Next time I'll be taking a long hard look at the fuel tank and having a bit of a re-think...

This month's Heroes list:
B&I Engineering (01484) 511534
Paul Coward for the loan of his Transit van.

Dr.Rod.