Removing Stuck Pistons from Two-Cycle Headless Cylinders
(Page 5 of 6)
May/June 2001
Richard A. Day Jr
Assuming the piston cannot be withdrawn by hand, the following
overall actions are suggested. Push the piston in and out several
times as outlined above. If this fails to permit hand withdrawal
and it is obvious the piston is no longer stuck hard then a simple
withdrawal device can be constructed that consists of a metal tube
large enough to permit the piston to clear it in the withdrawal
process.
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Square the ends of the tube in a lathe. Make a cap similar to
the one used to break the piston loose in the first stage of
removal. This time bore a clearing hole in the center for a '
or 5/8 piece of All-Thread rod. Make up a
yoke out of scrap steel stock which will permit clearance of a
piece of shaft bronze or steel shaft approximately
3/4' in diameter.
This shaft wrapped in a piece of sheet lead to pass though the
connecting rod 'BIG END.' The piece of sheet lead to
protect the inside surface of the big end from damage while
applying pressure in the withdrawal process. If one has a piece of
stock the approximate diameter of the 'BIG END' then this
will work even better without the need for the sheet lead pad, as
the pressure will be distributed over more of the bearing surface.
In any case we are not going to put excessive pressure on the
connecting rod in this process, as we have already reduced the
stress problem significantly. The piston should easily be withdrawn
by placing a washer and nut on the outer end of the All-Thread and
tightening it down, thereby withdrawing the piston without
significant pressure.
It has been my unfortunate experience that attempting to
withdraw a piston using the connecting rod before breaking the
piston loose destroyed the connecting rod in the process. One can
use a combination of the hydraulic method to start the movement of
the piston combined with the connecting rod pull method if
the piston has first been moved slightly with little worry
of damage to the connecting rod. If the piston has not moved, take
it easy trying to add the pull on the connecting rod to break it
loose.
Never having needed to use this technique for a four-cycle
cylinder, there seems to be no inherent reason it should not be
equally successful, given the problem of sealing the valve seats
may be more complicated.
In conclusion, make it a practice to always place a sheet lead
pad between a flat rough iron casting and a flat or machined
surface when applying pressure in a hydraulic or mechanical press.
A tiny raised imperfection in a flat iron casting can cause it to
fracture starting at the raised point even though it may only be a
1/32' above the rest of the casting. A
couple of 1/8 thick sheet lead pads will help
distribute the stress and usually protect the casting from
fracturing. The lead mold technique also works well with castings
that have more irregular surfaces and it is well worth the extra
trouble to use the lead mold technique.
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