how do i tighten the chain on my yamaha yz 125, 2003 model?

Answer 1

Look in your owners manual. Long travel suspension (depending on configuration of pivot and drive sprocket) requires the chain to be quite slack at rest, or else when the suspension is compressed, the chain will tighten up and cause damage to your machine.
I have had to replace 3 broken countershafts on different TTR125s over the last 6 months, all just down to the owners setting the chain too tight.

(for you TTR125 owners, the chain; when the machine is upright and suspension is unloaded, should just touch the rearmost part of the underside of the black plastic swingarm protector / guide, when lifted with a finger. Of course this is at the tightest point of the chain. Any tighter and you WILL break the countershaft at the kickstart idler end, and if you are really lucky, require new crankcases too, as the internal damage will ensure that no oil can be fed to the gear wheels under pressure).

Answer 2

From the previous answers, you should now know how to adjust your chain.
You have to know the chain "slack" specs (how loose or tight).
Make it to tight and it will -
Possibly snap the chain and it could put a hole in the crankcase.
Get tangled in the rear sprocket, lock up the rear wheel and cause an accident.
Whip around and injure you.
Put strain on the countershaft bearing, which could damage the transmission.
Ware out the countershaft seal, causing it to leak.
Ruin the R wheel bearings.
Ware down the F & R sprockets
To loose -
Fall of the F sprocket and put a hole in the crankcase.
Fall off the R sprocket and lock up the R wheel.
Please purchase a shop manual.
http://www.motocom.com/motorcycles/

Answer 3

with wheel of the ground slacken rear axle then turn the cams on each side the same positions tightening the chain then turn wheel around until the chain is in its tightest place the chain then can be finall adjust about a inch of play up from rest .tighten axle . dont have chain to tight for it will ruin bearings and the chain and sprockets

Answer 4

Yeah you just loosen the rear axle a bit and then turn the adjustment bolts (one on each side) near the back of the swingarm. There will be markings on each side of the swingarm and on the chain adjuster. Make sure the line or arrow on the chain adjuster points to the same mark on both sides to ensure the wheel is straight.

Answer 5

Look at the back wheel, near the spindle, you will see a groove with adjusting nuts, slacken and pull back, tighten, done, OK.