Some dirt bike nut HAS to know the answer.....

Kamakiri

The New Dynamic
On my Yamaha YZ80 frame, the rear wheel uses a 428 chain. Since I'm mounting a Briggs engine, the only centrifugal clutch I can get is for a 420 chain. I can't get a 420 rear sprocket, or a 428 clutch.

How different are these chain sizes, or does anyone have any idea how I can do this? HELP!
 
How about a jackshaft and pillow blocks?

If you wanted to use this approach a torque converter will kick ass over a centrifugal.
Just think of how many laughs your boys can have watching that little machine tip Dad right over backwards.
 
Krause quoted me 219.95 for the back sprocket and chain. I may go that route, if I can't find a cheaper alternative. More than the bike's worth, but it will git er done.

Stupid question. What's a jackshaft?
 
A jackshaft is basically an adapter. You run your 420 chain from the cent. clutch to a smaller sprocket, also 420. You simply take a piece of bar stock, or pipe maybe strong enough and much lighter, and weld a 428 sprocket to the other side, with the same diameter, and run the 428 chain back to your rear sprocker. Pillow blocks are a chunk of usually cast iron, kind of horseshoe shaped, that let you bolt them down, so the bearing can't move. It both locates and lets a shaft spin. The bearing is held inside the pillow block, you can get them in most any size.

The only thing about a jackshaft on a YZ80 is, where would you put it? how about this, are these steel sprockets on the rear, or aluminum? If they were steel, what about just getting a 420 sprocket welded to the 428 sprocket? Might not be pretty, but it would be simple. drill or cut out notches for the rear sprocket bolts, so you can take the whole thing off easy, and there ya go. I would think that would be the easiest solution, and probably the cheapest. You don't want too much in between teh front and rear sprocket, because you will have chain bind during your suspension travel. If not, email me a pic, I'll see If I can conjure something up for you, I MacGyver stuff for a living! Crexrun
 
Just get the rear sprocket with a 420 pitch in Hi-Carbon Steel - $69.99.

Get a cheapo RK 420 chain from your local MC shop for $20 or so.

The countershaft sprocket should be fine, and if it's not, you should be able to get one for ten bucks or so from your local mower shop.

Of course, the most important thing is to make sure the countershaft sprocket and the rear wheel sprocket are aligned properly.
 
theodoric said:
Just get the rear sprocket with a 420 pitch in Hi-Carbon Steel - $69.99..

Okay, I want to get this done today if I can. When I called as I mentioned, Krause quoted me 219.95 for the back sprocket and chain. I can't see where they would have the 69.99 option if they quoted me 219.....is the cost in the chain or something?
 
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