It seems the new front sprocket bolt holes are slightly smaller and in turn the sprocket holder doesn't exactly match up. At first I thought it was my stupid idea to use R version sprocket kit that's the problem here but turns out it's not.

I looked up the Yamaha Original part numbers for the bolts and the sprocket holder for XT 125 X/R 2008 and they are exactly the same.

The highlighted part numbers are the same for both X and R.

The sprockets I ordered are by JT Sprockets and when I looked up the front sprocket sizing on their website, they are also exactly the same: XT 125 X 2008 and XT 125 R 2008.

Now this is what I received. The new front sprocket (on top) has the same part number as the one listed on the JT site, it also fits in nicely to the drive. However, as you may or may not be able to tell from the picture below, the bolt holes for the new sprocket are slight smaller than the old (bottom) and the sprocket holder (right) doesn't align correctly with the new sprocket.

Is it possible that I ended up with a defective front sprocket (if that's even possible), should I just order the Yamaha original front sprocket instead?

P.S. The rear 50T R version sprocket fit nicely on to my X version.

P.P.S. Too many sprockets!

so dont the bolts screw into the new sprocket john...too big?

Yea, too big.

well i'm surprised at that, it's no use fitting smaller bolts because the holes in the plate will be too big and it's risky..best get a refund and buy yamaha one then

Really weird, oh well, trip down to the dealer tomorrow to sort this mess out.

Finally got it sorted. Turns out the previous owner somehow used a pre-2008 front sprocket kit which used a different sprocket holder and bolts. Ordered and fitted a matching holder and bolt set and now it's running smoothly.

For any XT 125 X owners that have thought of going two teeth up on the rear sprocket, I highly recommend you do when a change is due. My XT feels a lot more responsive now and a lot faster off the lights. Top end is not affected, in fact, I'd be lying if I said it's not slightly faster - maybe it's physiological but a definite worthwhile upgrade!

So how many teeth have your sprockets got?

Original X - Front: 14 Rear: 48 Chain: 428-128

Current X - Front: 14 Rear: 50 Chain: 428-130

I'll try it next time I replace my chain & sprockets.