To make a long story short(er):
fortunately I have friends in the USA who are waaaaaay smarter than I am.
David in Santa Fe dug into the problem and came up with , what I believe is,
the perfect explanation. There's even a term for it:
The easiest way to explain it is quote from the link to KIWI Indians
that David provided:
"...Cork screwing is when the flywheels are fitted between
the case halves and are rotated, they pull to 1 side or the other..
[ which mine does]
"... During service cork screwing causes side
loading (thrusting) which will cause damage to our lower end which is usually
evidenced by grooved or blued thrustwashers.
...in other words; 'grinding' the thrush-washers/shims and the result
will be a larger end-play...as I have now
"...Possible causes are flywheel
misalignment, pinion and drive housings out of alignment (possibly caused by
improper installation), mismatched case halves or case halves have damaged
mating surfaces (causing cocking)
What I DO know is that my cases were 'matched' and line-honed,
so I took out the manual and went through the flywheel checking procedures:
First a visual check, for what the manual calls
"truing the flywheels"
..by holding a scale to the face of both wheels
to check wheel-alignment
Whooha, mine didn't quite pass the test.
One side was like this ( note the distance between scale and 'lower' flywheel ):
....and the opposite side ( 180 degrees around ) had just a tiny bit of distance
but the other way around ( at the 'upper' flywheel )
Then the manual calls for a way to "true up the rotation of the wheels"
by testing them in contraption like this
and measure the "high spots" ( out of true ) on each wheel.
The height of these spots should be no bigger than 0.002" / 0.05mm
Borrowed this nifty thingy from a friend
and measured both sides
The high spots were 0.004" / 0.10 mm and 0.006" / 0.14 mm,
so that's twice and three times what it should be,
so obviously the two flywheels are out of true, in relation to each other,
making the assembly turn in a sort of 'tilted' whooply manner , causing the corkscrewing.
The KIWI link explains how to check for corkscrewing:
"...To check for cork screwing, rotate flywheel
assembly in 1 direction and see if it winds towards one side of the case. Now
rotate flywheel assembly in the opposite direction and see if it cork screws
towards the opposite side. Repeat this procedure several times ensuring that
"you" do not cause the side thrusting
....and YEP that's exactly what happened.
I rechecked ( to make sure it wasn't the contraption on which I rotated it, that
somehow made it move sideways )
by turning the crank assembly so left side rested on the right side of the contraption
and yep, the result was the same but of cause it moved sideways in the opposite direction
Bad news that it's out of whack, but then again: it's in fact GOOD news,
as the source of the problem is now found and it's relatively easy to correct
According to the manual, one simply take a big lead-hammer and whack them good
till they are true .
Seriously (!!!). That's what the book says.
I don't have the nerve for that, and anyway I'll take it to the machinist to
examine the rod bearings ( though I can't find any undue play ) and put
the thing together in a correct way.
What I did find ( very much in accordance whit what KIWI describes )
is some discoloration and marks on the shim on the left side
from the 'grinding' caused by the corkscrewing
One other thing I checked was the flywheel balance.
This is a new one to me, but the book calls for:
..assemble one piston with all the rings and attach it to the 'male'
..place them on two parallel bars or 'knife edges'
Now , the piston and rod assembly should stay in any
position if perfectly balanced........should be capable of of balancing in
any rotated position
I didn't have such a set of parallel bars, but put it back on the thingy
where the shafts rest on both sides on a pair of roller bearings.
I take it the result is the same.
First I removed the piston from the 'female' rod.
It was not in perfect balance. One thing is that the result probably isn'tquite
accurate due to the out-of-whack flywheels.
I'll do the test again when that thing is corrected.
If it's still out of balance the book says to drill 5/16" holes
through both flywheels on the 'heavy' side.
Never a boring moment...erh ?
BIG BIG thanks and kudos to David for solving the mystery
and to George of "Tri-Mac Speedsters" for patiently explaining the 'dynamics' involved.