Removing Stuck Pistons from Two-Cycle Headless Cylinders

By Staff

Copyright Retained

Before starting to remove a stuck piston from a cast iron
antique headless cylinder, it is important to understand that
antique cast iron is not cast steel. Much of it when broken is
quite black as compared with modern so-called cast iron, which is
typically light gray in color. A good way to determine if that
rusty cast iron antique toy is genuine or a modern reproduction
someone buried in a manure pile to make it appear old is to file a
small area. If it turns up gray don’t pay an antique price for
it, as it is probably a modern reproduction.

Antique cast iron is much like a ginger snap cookie in that it
breaks quite easily, particularly if the stresses on it are
not reasonably distributed over the entire casting.
This
explains the problem of welding cracked cast iron unless it
is heated uniformly and cooled under controlled
conditions.
It is far better for an amateur to repair a
cracked water jacket with an epoxy compound than risk further
cracking, or worse, wrecking the cylinder by welding or brazing
without proper heating and cooling.

The following are the successful methods I have used to remove
badly stuck pistons from headless cylinders. There are other
possible approaches, but having unfortunately learned the hard way
I now stick to the techniques that have succeeded for me without
destroying anything.

There is one technique I have always wanted to try but not
having an atomic power plant with its endless supply of boiling
water I doubt many will be able to take advantage of it. It seems
that some success has been obtained by boiling the cylinder in the
cooling water of the power plant for 24+ hours and the story goes
the piston just fell right out. I wonder???

The easy way to move the piston in a headless cylinder is to
fill (leaving no air pocket) the area above the piston with oil.
Plug any ports. Adapt a grease gun fitting to a bushing which is
screwed into a spark plug hole. A few squirts of grease from the
grease gun will generally move the piston with a minimum of stress
on the cylinder and piston. This presumes of course that the
cylinder walls below the piston skirt have been cleaned of any rust
buildup and lubricated with one of the penetrating oils such as
WD-40 or equivalent. Unless there is a space between the piston and
the cylinder wall, I have had little success with any of the
penetrating oils succeeding in breaking the rust seal until the
piston has moved a few thousandths. It is prudent to dig out as
much rust as possible between the piston skirt and the cylinder
wall as there is a normal gap of a few thousandths. (More than a
few thousandths in a badly-worn engine)

Perhaps your friendly dentist will give you a few of his or her
discarded tools. They are tough and great for getting into tiny
cracks and openings.

The success in removing a stuck piston lies in the preparation.
It is so easy to destroy an irreplaceable part; therefore, careful
preparation is mandatory.

The hydraulic method is probably the best, least stressful and
easiest method to remove a stuck piston. It is possible to break
out the center of a piston in those cases where the piston is not
particularly rugged in that area. Fortunately most two-cycle
pistons have a raised baffle next to the intake port and most are
cast as a portion of the piston. The only two-cycle piston I have
ever seen where the baffle was riveted to the top of the cylinder
is the piston on the first Palmer Marine engine ever made.

The cast baffle makes the piston head much more rugged than in
the four-cycle piston. In any case I have never experienced
breaking out the center of a piston using the hydraulic method of
piston removal.

The one method that will guarantee breaking out the center of a
badly stuck piston is putting a steel rod down through the center
of the cylinder from the top and trying to hammer or push the
piston down with a press.

There are complications, however, that makes a seemingly easy
task a real problem. Suppose the cylinder is headless and for a
two-cycle engine with the piston head stuck below a port. In this
case it may not be possible to seal the port (or ports) so the
hydraulic method can be employed.

A small flashlight bulb soldered to a couple of feet of
approximately 22 gauge insulated wire coupled to a six-volt
transformer makes a great inspection light to get a look inside a
water jacket or cylinder where the piston is not removed. It may be
possible to introduce the light through one of the ports or the
spark plug hole. Small dental mirrors work well in those cases
where they will fit through any openings into the cylinder or water
jacket. Fragments of mirrors are sometimes useful in trying to get
an idea of the condition of the cylinder or water jacket.

If examination of the cylinder wall above the piston indicates
only superficial rust, then the following can be used to remove the
piston.

This method of removal first pushes the piston further into the
cylinder until the ports are covered. Once the ports are covered by
at least ‘ of piston travel, then the hydraulic method is used
to push the piston back out to the edge of the ports.

The oil is allowed to drain down and the piston is then pushed
back in again, this time perhaps an inch above the ports. The oil
is then replaced and the piston pushed back to the edge of the
port. At the same time this has been going on, penetrating oil is
liberally applied to the piston skirt. In some cases it may take
three or four back and forward movements to permit the piston to be
totally withdrawn.

When withdrawing the piston, make note of the angular position
of the piston ring gap, as the rings in old-time two cycle engines
are normally pinned so they don’t rotate and get hung up in the
ports. Some pistons may have a ring near the bottom of the piston
and this ring never travels far enough up to trap in one of the
ports. Such rings are not typically pinned.

Also check that the piston baffle was adjacent to the inlet
port. This precaution can save a lot of grief when reassembling the
engine. On occasion I have found a previous owner must have
disassembled the engine and reversed the baffle so it was adjacent
to the exhaust port. This could explain why the engine no longer
was in use, as it probably didn’t run very well if it ran at
all. When removing the rings, keep in mind there is a top and
bottom to each ring and turning a pinned ring over can make it
impossible to correctly install the ring without it hanging up in
one of the ports.

The set up for pressing the piston IN is quite different
from a hydraulic push OUT when the ports are covered. In this set
up we first create a lead mold to distribute the stress over the
entire cylinder head.

1. Plug any openings in the cylinder head area where they may be
covered with lead. Otherwise you will have a problem withdrawing
the lead mold and cleaning out the lead in the openings. Wooden
plugs work well and don’t need to protrude as pipe plugs, etc.
may. Set the cylinder out in the sun for six to eight hours to
remove any chill in the iron. This slow even method of heating is
much less stressful than trying to heat it with a torch. Both the
inner jacket walls and the outer jacket wall need to reach about
the same temperature, so aim it so the sunlight can penetrate into
the bottom of the stuck piston. Rotate it from time to time to try
and spread the heating as much as possible all over the cylinder.
If one has an oven, raise the temperature to approximately 150
degrees over a period of several hours. Keep in mind we are not
trying to prepare this cylinder for welding, so don’t get the
temperature so high that the lead will not solidify and we
don’t want to risk the cylinder to cracking due to rapid
uncontrolled cooling from a very high
temperature.

We are just trying to remove the CHILL so the
lead will follow the contours of the head and not stress the
cylinder with a high heat shock.

2. Make a circular dam out of sheet metal approximately 3′
high.

3. Make it big enough in diameter to permit lowering the
cylinder, head end, into the middle of the dam with enough
clearance to make it easy to pour in the molten lead.

4. Set the dam on a piece of steel plate ‘-‘ thick.

5. Use several pieces of steel as weights to momentarily hold
the dam in place on the steel plate.

6. Melt five to ten pounds of scrap lead in a pot.

7. Pour molten lead into the dam to a depth of about
3/8‘-‘

8. Let it harden for a minute or two. The initial pour is to
simply seal the bottom edge of the dam from leaks between it and
the steel plate.

9. Position the cylinder head, down, in the middle of the dam
but not touching the lead already solidified.
About a ‘ gap should suffice.

10. Pour in enough lead so it just begins to rise above the
crown of the head portion of the cylinder.

11. Do it in one quick uninterrupted pour but don’t put in
so much molten lead that it comes up the side of the cylinder more
than about ‘ as it may trap the cylinder when you are ready to
remove the lead mold.

12. Pouring the molten lead into the dam forms a mold around the
cylinder head that will distribute pressure over the entire
cylinder head following its contours precisely.

Without the lead mold any high spots could
cause the cylinder to crack when the piston is pressed into the
cylinder.

If the second pour is done in the press one can use the ram of
the press to vertically locate and support the cylinder prior to
making the second pour.

The reason for the cylinder not to touch the lead from the first
pour is to insure that no air gap is created in the second pour and
the space is filled with lead supporting the head in this most
critical portion.

Prior to mounting the cylinder on the press, a steel tube needs
to be obtained and machined to fit within about a
1/32‘ clearance in the cylinder bore. The
tubing should have a wall thickness of at least3/8‘-‘. The tubing should be long
enough so the connecting rod can stand straight up in the bore and
not quite reach the top of the tube. The ends of the tubing need to
be turned square to maintain uniform pressure all around the rim of
the piston skirt and with a turned plug that the ram will press
against.

A 1′ thick steel plug with a lip equal to the tube wall
thickness is turned with a small clearance that will allow it to
easily fit into the top of the tube. This plug and the bottom plate
will need to be backed up with sufficient steel support so that the
pressure from the ram will not collapse the bottom plate under the
lead mold or the plug in the top of the tube.

When applying the pressure from the hydraulic press, take it
easy and let the pressure build up gradually. If your press
doesn’t have a pressure scale, apply some pressure and add some
penetrating oil around the piston skirt. Let the pressure sit for
30 minutes. Check for any movement. If none, add a little more
pressure and wait; repeat this process until something gives. I
hope that it isn’t the cylinder. On one occasion I added dry
ice crystals to the piston and within about a minute the piston
broke loose. I should add that the cylinder had cooled down from
the day before heating. I would not have added the dry ice if the
cylinder was still warm. In this case I was willing to risk
cracking the piston (it didn’t), as the cylinder was critical
but a replacement piston was not. Scribing a few marks on the tube
where it enters the cylinder bore will make it easy to determine if
any piston movement has taken place. Often one will hear a pop when
the rust breaks loose. Immediately back off the ram, remove the
tube and examine the piston both in the ports and at the piston
skirt for evidence of movement. Liberally apply penetrating oil to
the piston and let it sit overnight once it has moved. You know
it’s going to come out and a little penetrating oil and time
will only help. It may be that once the penetrating oil has done
its work the piston can be pulled out by hand without further
serious work.

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.

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.

The basic idea is to avoid a point area pressure buildup by
spreading the stress uniformly across the casting.

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