Removing Stuck Pistons from Two-Cycle Headless Cylinders

| May/June 2001

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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