Recently bought a spare engine that needs an overhaul.
I ordered most parts needed for the job but when I opened the case I noticed the left crank shim was missing and it almost looked like the bearing didn't sit deep enough in the seating.
What is the correct way of measuring this up and how much "play" is allowed after the correct size shims are fitted.
Thanks. Pieter

Not all the DT175's were the same...  later ones did not have shims.  What are you working on?  Year?  VIN prefix? 

DT175B (1975) vin prefix 576

I've seen some of those without a shim but not sure it was correct...  often the crank wheel rubs the case without a shim.  But anyway, here is a summary of the procedure from DEET:

yamaha-enduros.com/index.php/forums/gene...build-problem#123972

I don't know if it makes a difference or not, but 576 is the model code for the 1976 DT175C. 

Forgot to say I've also seen that era DT175 with a shim on BOTH sides of the crank. 

Complicates things.  Basically crank (connecting rod) needs to be centered in the cases.  Some of the service manuals in the tech library have engineering drawings of the crank and case that could help.

According to the service manual I use DT175A, B, C are the same.
The only small thing I noticed so far is a steel ball between pushrod 1 and 2 for the clutch. 
But is unclear to me when they made that modification.

From the exploded views in the book you need a shim on both sides of the crank.
CMSNL sells different thickness shims to choose from, assuming this is to set the thing to true centre and leave some "play"

You're talking left side--mag side. I can't see any sense in having one on the left as it' held over to the right by the crank gear-nut. If left bearing it home in the case there will always be a gap to the crank. Ok if the bearing wandered out it could stop the possibility of the bearing outer ring rubbing on the crank wheel but i think they have a light step on the crank to stop that happening. A shim would save the bearing wandering over & stop any possibility of rubbing but with everything as it should be fitting a shim would only spin around free & do nothing. Now i'll go looking at parts pics & see if i'm talking rubbish.

 Ok that stuffs my theory so i dunno, shows a shim Jim!!. That's a 1975 partzilla drawing by the way.

So ok if you fit a shim & have the bearing against it, then slide the crank into the right side & bolt it there with the crank nut. Then pull the left case onto the bearing it should stay neat & neutral against the washer--but nothing ever goes to plan 100%. Maybe after everything is assembled & tightened just give the left bearing a tap, then a bigger tap, to make sure its against the shim so shim isn't flailing. Ignore me--too much time on my hands lol.