RE:New pistons & liners(was Motronic pistons)

["John Fielding" <johnf@domain.elided>]

Hi all AD readers,

Several folks entered into the discussion as whether it was necessary to
remove the pistons from the liners before assembling into the motor.
Sitting here thinking about it later I realised - Wow, that's a really time
saving trick!  I wonder how one manages to get the connecting rods into
place without removing the piston from the liners??

Seriously - IMHO any manufacturer who assembles piston rings and then
inserts them into the liners really should do this in a clean area.  And I
have only ever come across one incidence were the rings were already fitted
to the pistons, in every other case the rings were supplied loose with the
pistons.  In fact when I built the Ford V8 motor for my new GT-40 the
pistons and rings were priced separately snd came from different
manufacturers.

I prefer to build motors slowly.  Every component is cleaned, inspected,
tolerances checked etc etc.  Only when I am 100% sure everything is right
will I start doing a trial build to confirm, for example the crank rotates
smoothly with no tight spots.  Motto - build slowly and carefully with the
right parts and your motor will last a long time beore it needs any
attention.  Especially true for motors intended for racing!

One final point about locating the gap in piston rings.  I along with
thousands of others always set the rings so the gaps were arranged equally
spaced around the pistons.  It is said by the "books" that this reduces
blow-by.

Well, recently I came across a mechanical engineering magazine (can't
remember the name as it was whilst sitting in the waiting room at the car
service depot) were the author explodes this as an a waste of time.
From research he conducted with various motors he discovered that
the rings typically rotated around the piston at approx. 30rpm when
the motor is revolving at 5000rpm.  Not only that but the first, second
and oil control rings all rotate at different speeds, so although they
might start off arranged correctly it would take very little time for them
to fall out of sync!

It would be interesting to do an experiment and set the ring gaps on a
piston and then run the motor for a short time and remove the piston and
examine were the gaps were then.  Anybody got a guinea pig motor and wants
to try it out?

Note : 2 stroke owners need not apply as in these motors the rings are
normally "pegged" to prevent them rotating and hanging up in the transfer or
exhaust port.

just thought you would like to know.

Now off to replace the blown donut on the Alfetta prop-shaft!

John
Durban
South Africa
Alfetta 1.8L turbo - hillclimb track car
Fiat Uno Turbo - daily driver - occasional track-car
Ford GT-40 replica - starting to take shape!

"Too old to rock & roll, too young to die"    Jethro Tull

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