I'm looking for information on the yz125 crank shims. Is there one size or different size options? No information in the service manual.

There are several different sizes, used on 175 engines. I would think the YZ is the same? Very accurate measurement, is required to determine shim size.

No idea if i'm right but MarkT & other may know.
04 as the end number has me thinking 0.04mm or 12 thou?? #16.

www.partzilla.com/catalog/yamaha/motorcy...-piston-yz125a-b-c-d

I can't find any info on the measurements between crank and case. 

The DT175 of that era is simply a "detuned" YZ125 and has the same crank arrangement.  That probably doesn't help much though.  Normal process is to reuse the shims that came out. That's not always possible though.

On the old forum I think it was DEET that posted a lot of good info on this topic.  I would contact him.  He might even have shims. 

Here's my "hack" approach.  You want the crank centered and not rubbing...  the critical side is the clutch side because the nut pulls it tight. I always check before assembly that it's not rubbing there. 

Super accurately measuring the bearing width with cases torqued and measuring crank width super accurately is a challenge for me.  Later models had a "built in" shim on the clutch side and nothing on the ignition side.  I use that as a guide.  So what I do if I have no clue on the shims is shim the clutch side, install crank into clutch side case only with gear, spacer, nut...  See if it clears case okay.  It always has.  Then I leave the ignition shim out.  never had a problem yet. 

Final check after assembly is seeing if crank looks centered...  it always has.

My concern with shimming the ignition side is too tight would be bad...  too loose and the shim wouldn't do anything anyway.  Later 125/175 didn't seem to need an ignition side shim so I use that logic to justify my hack. 

I don't recommend you follow this, best to contact DEET or someone and see how to do it right.

Thanks Mark. I have rebuilt 2 yz125s and both had good original shims. I did make sure the crank was centered in the cases. Building one now that is missing the shims.

The 74-76 era of that bottom end design is lacking diagrams... The specs do show that the crank width specs are the same as the earlier AT/CT series. Bearing and seal sizes are the same too.

Here's an early diagram from the CT1 manual... again, probably not too helpful... DEET and/or Enduronut might have solid answers.

Having looked at many Yamaha parts lists, it would be interesting to know how the crank is centred in the cases, when the only shims listed are for the flywheel side, and the crank is located into the drive side main bearing, by tightening the crankshaft pinion? I wasnt able to work that one out at all...................lol

Yam-Fan, you haven't looked very hard.  In fact the parts list for the engine in question (76 YZ125) still shows shims on both sides.  www.partzilla.com/catalog/yamaha/motorcy...-piston-yz125a-b-c-d

Originally there were multiple thicknesses to choose from...  hard to find shims and parts lists are not complete.  Info on shimming is sparse as well.  



 

The motors I have measured (reasonably accurately), had about .3mm clearance, between the crank and bearings.

It would be a little more, with jointing compound, but I was unable to work out how to centralise the crank, when there was only .3mm clearance?

I would think there would be need for some clearance, to account for expansion, so unless you can measure the crank width, and distance between the bearings accurately, or have the original shims, and no new parts have been fitted, its probably safer to leave them out?