Richard Smith <richard+1b5d11@mole.demon.co.uk> writes:
>>Vern Klukas writes:
>> The real pros would measure all the various components and then
>>calculate the
>>clearance.
>
>Rubbish!!
>
>The *real* pro uses 'plastigauge'. Most pros grind the crank to the
>required tolerance and fit the bearings it says in the book. Most pros
>couldn't calculate the difference between the main bearing housing diameter
>and the diameter of a trashcan lid!
Not rubbish. When I said real pro, I meant real pro. The guys that build
engines for Nascar, Indy, F1--any of the professional (in that big, big
bucks are involved) motorsports do not use plastigauge. Aircraft engine
rebuilders do not use plastiguage. In fact, they would probably take
offense to the suggestion that they do. It's a fine idea but is not
reliably accurate. The accuracy depends on the plastic thread being an
accurate and repeatable size, which just ain't so. I have seen the same
bearing and journal show a _one and a half thou_ difference between six
difference lots of plastiguage, during a test we ran once. It was then that
I invested in a good bore guage and outside mic set and chucked my supply
of plastiguage in the trash.
In any event, measuring a thrust with plastiguage is just plain impossible,
as you must slide the thrust bearings and the crank thrust surfaces
relative to one another when you are assembling, and the plastiguage must
be squashed without any sliding or scuffing to get anything like the real
clearance. Also, you cannot apply a repeatable amount of 'squash' in this
circumstance, even if you could assemble the crank and thrusts without
sliding.
OTOH, a lot of people do use it, and the motors don't blow up. I think that
is more a factor of civilian uses of the machinery being at a level far
below the stress and hardship of racing or maximum use of the motors.
_____________________________________________________________________
Vern Klukas I'm a little teapot
vernk@carver.dataflux.bc.ca or Short and...
ug141@freenet.victoria.bc.ca or
inkspot@carver.dataflux.bc.ca
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