My Method of Removing Stuck Pistons


| November/December 1998


607 SE County Road 234 Gainsville, Florida 32641-1303

I've read with interest the many methods submitted to your magazine for removing stuck pistons. I'd like to add my own experience with a 4 HP Mogul engine in hopes that someone might benefit from it. The engine had been sitting out in a pasture for over a year with the head off and at such an angle that water was trapped in the upper two or three inches of the exposed cylinder wall. This particular model had an inspection plate on the rear of the base that allowed me to release the connecting rod so the cylinder and hopper could be removed and worked on as a unit. After making a wooden saddle and clamping the unit to the workbench, I removed the rusted studs and replaced them with new ones. Next, I cut a series of 1' round oak blocks, just smaller than the cylinder diameter and also cut a 1/4' steel plate slightly larger than the head. Using the head as a template, I marked and drilled six holes 1/64' oversize for the studs. Then, by inserting enough wooden blocks to insure a space between the top of the block and the bottom of the steel plate, I threaded on a set of coupling nuts for maximum thread contact. I began to tighten the nuts moving from stud to stud in a clockwise fashion. I went around and around the studs, creating a spiral pattern of force until the piston was finally free. At times I was able to turn individual nuts only five degrees before moving to the next one. I didn't use a torque wrench, but instead went by 'feel' when deciding how much to tighten each nut. I also waited at least 30 seconds before moving to the next stud, tapping around the perimeter of the steel plate in the meantime. After the piston was past the worst area I was able to take several turns per nut, though it drove hard until it was completely out. The piston was easy to salvage by simply cleaning after the wrist pin, rod and rings were removed. The rings had to be chipped out and measured. They were ordered from the Superior Piston Company and fit perfectly after notching for the groove pin. I took the block to Central Motors Machine Shop to be bored and sleeved by Lee Baker. He did an excellent job and gave me a friendly reminder not to forget to drill the piston oil hole through the sleeve! After total re-assembly it was very difficult to turn the engine over unless the compression release cam was engaged.






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