Removing Stuck Pistons from Two-Cycle Headless Cylinders

(Page 4 of 6)

May/June 2001
Richard A. Day Jr 
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4. Set the dam on a piece of steel plate '-' thick.

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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.

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