m - 20 bearings question

[James Niebrzydowski]

I am rebuilding a 72 six days sachs motor. This is my the first time fitting new 3 piece bearings. I used a new gasket when measuring the distance from the crankcase to the bearing.I shimmed the bearing to have .003 to .004 of an inch clearance. I then soaked the gasket and put the crank in and put the cases together. The crank moved smoothly but not as freely as I am used to compared other 2 stroke motors with regular bearings. The question I have is should it feel not as free as regular crank bearings. I am sure my measurements were correct and the shimming was right. I did use a new dry gasket for the measurement and was wondering if it might have compressed after I wet it and closed the cases up. I then split the cases back apart and removed .005 of an inch from the crank and put it back together and the crank moved smoothly and freely like regular bearings.

Questions
 1  should it feel as free as regular 2 stroke bearings when assembled ?
 2 The manual specs .0019" - /004" axial play ,should I be able to measure axial play of .0019" - .004" with new bearings and the motor assembled ? Note: with .005 shim removed I still have zero axial play.
 3 should I have soaked the gasket before measuring?
 4 should I measure everything again, do the math, shim it and not worry about how it feels?
 5 being that I soaked the gasket and closed the cases, when I do get everything shimmed right can I still use the same gasket?

James

[gooddirt]

You might  have to factor in the gasket compression . Do you have the OEM or black after market? Watch your torque on the case screws.

[James Niebrzydowski]

I am using a black after market.I have the original one that was in the motor.

[JP Morgen]

I have found it difficult to accurately measure and shim the bearings on paper, so what I do is assemble the motor with .002-.005" less shimming than calculated, mount the motor in a big vise, attach a dial indicator to the crank and push and pull to get the actual clearance, then add the necessary shims to reach my desired clearance. I shoot for .001" on all of the various motors, 100-400cc, that I have built with no problems and very good performance. Make sure your third, standard, main bearing is not introducing any side loading on to the crank, and remember the aftermarket/modern crank seal have quite a bit of drag.

[James Niebrzydowski]

Starting off with less shims then calculated made this shimming process a lot easier. thanks JP

crank now has .003" play
main shaft has .004"
kicker has .003"
lay shaft has zero ?? will zero be a problem this is how it was when I got the bike ?

can I still use the new gasket for final assembly even though I used it for the shimming process

[JP Morgen]

zero clearance shouldn't be a problem as long as it isn't binding at all. You can use the same gasket.

[James Niebrzydowski]

Lay shaft isn't binding , Thanks JP for the confidence in rebuilding my first sachs motor

[James Niebrzydowski]

Now onto setting the mysteries shifting transmission. I have never even ridden a Penton.