Removing a Stuck Piston from a 2-Stroke Engine

One successful method for removing a stuck piston from a 2-stroke engine

Removing a stuck piston

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Recently a reader was faced with the problem of removing a stuck piston from a 2-stroke engine, realizing that the good old grease/oil pressure method would not work because of porting. Can't remember how he solved the problem, for trying to drive out the stuck piston with a narrow rod through the spark plug hole in the non-removable head is most hazardous for the future of the stuck piston.

As a recipient of a very ancient Vaughan 4 HP drag saw, I was faced with the same problem of removing a stuck piston. On this 2-stroke engine even blocking the intake and exhaust openings would not help because fuel-oil mixture enters the cylinders through large ports in the piston wall! Prolonged soaking of kerosene and penetrating oil did not seem to help the stuck piston any either. But there had to be a way of removing that stuck piston, short of using dynamite.

The piston was finally removed from the 2-stroke engine successfully as follows: (See diagram.)

Two pieces of 1/4" thick cold-rolled steel about 1-1/4" and 2-1/2" long were drilled in three places to allow bolting to the bronze connecting rod in lieu of the end cap and also to hold a long threaded bolt 3/8" diameter and 5" long. The crankshaft throw was turned directly down. The cylinder was placed over the crankcase mouth in its usual position and the long bolt protruded through the large rear hole in the crankcase. Two 1/2" diameter steel rods were placed across the end of the crankcase, one on either side of the long bolt and a large washer, then a nut was placed on the bolt and drawn up snug with a crescent wrench. Threads of the bolt were oiled liberally, more penetrating oil was sprayed into the cylinder and an old gasoline blow torch was directed at the underside of the cylinder base. When the cylinder began to feel quite warm, then the work began of turning the nut to draw the piston out. Due to a small boss inside the crankcase, the piston could be drawn out only about 2-1/2" at the first pass. However, large nuts set on edge were used as temporary shims between the cylinder flange and crankcase and work continued until only 1" of piston was still in the cylinder. The piston was subsequently fairly easily removed by hand. Two successive 3/8" bolts were needed to do the job for one was stripped due to the force exerted. The piston resisted removal every inch of the way.

There is undoubtedly a better, easiest way to remove stuck 2-stroke pistons but this method does work- safely.

Later model Vaughan 2 stroke drag-saw engines do not have removable cylinders. As 1 recently discovered to my chagrin, to remove stuck pistons upon such engines, the crankshaft must be completely removed.

One problem begets another. To remove the crankshaft, the whole clutch assembly has to come off. Sounds simple, doesn't it? On my other ancient Vaughan, the clutch was keyed to the shaft, and was rather easily removed by removing the locking bolt and by judicious use of a gear puller. So, naturally, since the clutches were nearly identical, the newer one would come off just as easily. Not so! I drew up on that gear puller until it seemed certain something would break. No soap. Tried heat, light oil, and tapping on the clutch and puller. Nothing worked. Was it welded on? I finally removed the puller and studied the clutch again for a time. What could be holding it? Then the possible significance of the two large unthreaded holes in the clutch hub suddenly dawned on me. Maybe it was threaded on. But threaded in which direction? Logic dictated a possible left-hand thread. O.K. But how to break it loose? This was solved by dropping two large bolts about 2" long into the holes, and putting a 3" length of 1" water pipe between the bolt heads and hitting the end of the pipe handle with a large lead mallet. After several tries, the clutch was loose with no damage. The Vaughan people undoubtedly had a special large 2-pronged wrench for this purpose.

That left the 2" nut that securely holds the flywheel. Few of us possess 2" open-end or box wrenches. (A new wrench of this type costs $40.00.) My little 10" pipe wrench barely spanned that huge rusted nut. The feeble force that I could muster was insufficient because the engine would rock on the floor as force was applied and because the wrench was too short. Then came the dawn again. 1 carried that heavy rascal back to the saw's A-frame, bolted it down, and increased the leverage on the poor little pipe wrench with the 3" length of pipe. It worked again-a left-hand thread.

With the nut off, the flywheel yielded easily to the gear puller. The rest would be easy. Simply pull the stripped crankshaft out and begin pulling the piston. But something was wrong! The end of the connecting rod, after the bolts and cap were off, was blocking the throw of the crankshaft. The piston would have to be moved forward farther into the head to gain room to draw out the crankshaft. Either that or cut off the connecting rod. So, light oil was fed into the cylinder from both ends and the cylinder was heated with the old gasoline torch. While the cylinder was still hot, the wrist-pin boss was given a solid rap, using the piece of water pipe and lead mallet again. After a few tries and some silent prayer, something gave, and luck again, the piston had moved just enough to allow removal of the crankshaft.

The rest at long last was easy. But this time, the only difference was that a length of threaded rod from the hardware store was used to draw the piston, because my bolts were too short for the purpose.

Contact Doc Shuster at 3535 Glen Oak Drive, Eugene, Oregon 97405.