I am building a DT175 motor from several boxes of parts, and wonder what is the correct way to set the crank shimming?

Shims are listed for flywheel side (0,3 and 0,5mm) and drive side (0.4, 0.5, 0,6 and 0.7mm).

The crank is obviously drawn up to the drive side main, when the crank pinion nut is tightened.

Seems to me the purpose of the shims is to locate the center of the crank in the center of the cases, and shimming the drive side would achieve that?

What I cant work out is what is the purpose of a shim on the flywheel side, given the fact that, It's either going to be spinning on the crank and doing nothing, or could be putting end thrust on the bearings, if not sized very precisely, with a little running clearance?

I have made a tool to center help check whether the rod is in the center of the cases, and its easy to achieve that, but would be very interested to find out what the LH shim is meant to do?

CSMNL parts diagram for 75 bike shows flywheel side shims at No13 and drive side at No19

Be great if anyone knows the answer to this.  Have measured both crank, and crankcase cavity, accurately.   

Without looking at the diagram i agree with all you're saying & have pondered the same question myself. The only way it would sit tight is if you fitted the left bearing on the crank & hard against the shim then bolted the crank to the right side then heated & dropped the left case on. Then i guess you have to hope the left bearing stays there & doesn't try to move out if not super tight in the case--& equally tight on the shaft. Maybe the shim is listed to give the outer bearing ring plenty of clearance to the crank wheels although i think the wheels are recessed plus there's a slight step against the crank. So i'm no help am i lol.

On my Ct1c I left the flywheel shim out by mistake and when I put the cases back together the flywheel rubbed against the case I thought what the heck is going on then I noticed the shim on my workbench had to take it back apart to install the shim and fixed the problem 

You're talking the right side shim?.
I wonder if that might hold true if the left one was left out & for some [not normal] reason the crank & its two bearings wondered to the left--would left rub on the case. All the same it can't be good to have a free wheeling shim. Wonder if you fitted a shim tight on the shaft so it stayed put incase its needed.

Thanks for your replies.

Bearing in mind the crank is drawn up to the drive side main, when the crank pinion nut is tightened, I think the purpose of the shims, is to equalize the side thrust on the main bearings, that comes about due to the helical primary drive gears?

I would guess there has to be some sort of clearance to allow for expansion, and an obvious need for the crank to run completely true?

Will try and find out for sure from a specialist crank rebuilder, and ask what sort of clearance is likely to be needed.

Yamaha shimmed that year on both sides.  Manuals have a crank width spec tolerance. You start with that width. Then you measure the width between the bearings and select shims to center the crank. 

I've been lucky to always have the stock shims which I just reinstall...  Forgetting to install one on either side can result in crank rubbing. 

Yes, the crank nut clamps the right side.  Left side is a fairly tight press fit into the bearing.  Crank stub needs to be pulled into the inner race of the bearing when assembling case halves.  Without the shim, the bearing can shift over and outer race will rub on crank wheel. 

Later models 175's (78 on) had no shims...  they machined the crank flywheels with a little "bump" that the inner race of the bearing contacts that serve as shims.

My advice is just use the shims



 

Thanks Mark, re shim, i did wonder if the crank wheel is recessed on one model or the other. Not going to pull mine apart just to find out [bottom end never been apart since new i 1970 lol]--stand back she could blow!!.