OK, here's a new one for all those who thought they've heard them all ... A friend of mine, an older man who doesn't get around very well, has had LB 2 cycle mowers for a long time. He wishes to continue to mow his front yard, close rear and sides, but I mow the 0.50 acres behind his house. He had a 1986 model LB that worked pretty well for a long time. I had been doing seasonal PM on it, and was doing pretty well for the age, and how he was using it. But, mid-season last year, he put gasoline (no 2 cycle oil) in the tank, and soon thereafter, it seized. I was not able to do anything with it. He happened upon a 1999 Silver LB, with a 2 cycle engine. It ran very well, and had not been used much. He did OK with it for the remainder of the seasson, until late in Fall, he put straight gasoline in the tank, and ran it only briefly, realizing his mistake. He intended to remedy the problem by pouring some LB 2 cycle oil into the tank, thinking he would "over oil" it. But, the added oil really gummed up the works. That was at the end of the season. I brought it to my shop this Winter and got it all cleaned up and running pretty well. Sometime during the time he started using it and when I saw it, one of the muffler bolts came loose, fell out and was hit by the spinning blade, breaking out the support boss, to which the bold was threaded. Now, only 2 of the 3 bolts were holding a somewhat deformed muffler. He never started it up after I delivered it back to him February, until yesterday. Before starting it, he put STP oil additive in the tank. Now, don't ask me why he put STP in the tank, but he did that. Then he put in straight gasoline, not mixed fuel with proper 2 cycle mix. He mowed a small area and it quit. I saw it today, and it is not seized, but I'm not sure of the damage. I am intending to drain out whatever I can and replaced with properly prepared mixed fuel. To my question: If the engine is toast, then one consideration would be replacing it with a 4 cycle Tecumseh, often used on these Silver model mowers. Is the bolt pattern the same for the 2 cycle LB engines and the 4 cycle Tecumseh? Could I make a one-for-one replacement? Anybody done this? Or, I could put in a short block. His history of dealing with 2 cycle mixed fuels is not good. His is about 70, only five years older than me, ... is this what I have to look forward to? I thought that maybe he could deal more easily with a 4 cycle engine at this stage of life. He doesn't get out much, so the hour or so of exercise is good for him, AND he really wants to mow a small portion of the grass for himself. Normally, I would NEVER make a split property, but I am making an exception in his case. He/his wife intend to stay in this single family dwelling a short time longer, then move to a condo, or some other maintenance-free facility. So, he isn't eager to buy a new mower (why he bought the second-hand one a year ago); the majority of his grass cutting days are in the past. Anybody have a suggestion to get this mower back in service for him, ideas I have not thought about already?