Chain Adjustment when changing sprockets

[swatdoc]

Here's a question I haven't seen before in the numerous threads I've seen on chain adjustment: does the amount of chain slack when the bike is on a center stand change after you have changed sprocket sizes? In other words, say you have your chain adjusted correctly at 2" of play with stock sprockets. Now you change to a bigger front sprocket and a smaller rear sprocket, then re-adjust the chain for the same 2" of play when on a stand. will the chain still be adjusted correctly?

I actually did the whole rear subframe and shock removal, lift the rear wheel so countershaft, swingarm pivot, and rear axle are all in alignment, then adjust for 1/4" to 1/2" play/slack in the chain. I then put the shock back on and then measured the play/slack from the chain slider mounting screw. Problem is after all that I changed rear sprocket size. I readjusted so I have my same amount of play/slack, but now I'm unsure if I'm still adjusted correctly.

[grayracer513]

The figures shown in the manual are a repeatable, easily made measurements based on the idea of having set the chain to 1/2" slack at the tightest point in the swing, the way you did. But, it is not a measurement of slack, just exactly, and you are technically correct in your thinking that the size of the sprocket will influence how far you can raise the chain above the swing arm with the same amount of true slack in it.

In the extreme, the radius difference between a 53 and a 39 tooth sprocket is 1.4", and without actually doing the trig, you can guess that the difference at the point at which the measurement is taken will be half that or so. So, you could guess at it, or you could do "the whole rear subframe and shock removal, lift the rear wheel so countershaft, swingarm pivot, and rear axle are all in alignment, then adjust for 1/4" to 1/2" play/slack in the chain" thing again with the new sprocket size to be certain.

[Fabwiz]

Geez... i just pulled the bottom bolt on my shock ?

[swatdoc]

Thanks Gray - I was kinda thinkin I'd have to re-do it to be absolutely sure but thought I'd ask the experts before going to all the trouble.

Fab - I'll try your method - way easier if it'll work on my bike! First time I did it all the stuff was off anyway

[Fabwiz]

Worked for me, 02' YZ426. Post on how it went I am thinking of regearing as well.

[grayracer513]

Fab - I'll try your method - way easier if it'll work on my bike! First time I did it all the stuff was off anyway

Pulling the relay arm bolt out of the swing arm is the simplest means of disconnecting the arm from the shock for this.

[swatdoc]

OK thanks Gray