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Yamaha YZ125 gear box question.

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I am rebuilding a 1996-2001 model Yamaha YZ125, its actually the last of the 2001 model with a 6 speed gear box. I have bought another gearbox/engine in bits but it turns out to be a 5 speed gear box from a later YZ125, possibly a 2002 model. Will the gears from the earlier 6 speed box fit straight in and work in the later 5 speed gear box or vice- verser or are the different. Any one know as im new to the yz range so i dont know.

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What are the numbers stamped on the left engine case half of the parts engine?

Should start with 5DH-XXXXX or something like it.

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The short answer is maybe. The cases look identical but have different part numbers. I think the tranny will swap but there a few things you will need to check with some calipers;

Set the tranny gear clusters side by side and measure the assembled width. If the gear clusters (that portion that fits between the bearings in the case halves) are within .010" and the shaft diameters are are the same size and length, then the gear cluster should swap.

Measure the width of the shifter drum and the diameter of the drum where it fits in the caes. They should match.

Check to see if the shifter fork shafts are the same diameter and length (they should be, they are the same part numbers)

Both trannys have 2 shift shafts and 3 shift forks.

My bet is tha transmission will swap.

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i have never done it, but from what ive read on this site, it will swap with no modifications.

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i have never done it, but from what ive read on this site, it will swap with no modifications.

Ther ya go.

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