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Lawn Boy F-series Carnage

5379 Views 9 Replies 8 Participants Last post by  Jimbird89
I know you guys love pictures, so I took some good ones for you. A guy brought in a 1991 Lawn Boy Commercial self-propelled mower. He said something in the recoil was bad because the engine would turn over sometimes, and other times it would lock up. Well, it wasn't the was the connecting rod. Depending on where the broken pieces floated around in the crankcase, it would either lock up or spin free. I tore it down for a rebuild today and it was NOT a good sight. I can't really salvage anything from the engine. I don't know why the rod broke, but I think it was an extreme case of hitting a solid object. The blade adapter was broken off the collar, the self propel pulley was split in 3 pieces and the center hole was much too large from bouncing around without the set screw being tight. There was a major blowout in the crankcase from the rod breaking. Bent reeds. The exhaust ports were carboned up so bad that it couldn't have been running well before it let go. The piston was scored, but came right out of the bore very easily and the rings were in good shape and free in the grooves, so I doubt it seized at any point. The rod bearings smelled like burnt popcorn. I am going to use another block, crank, and rod. All other parts will be new. I am the only guy in about a 75 mile radius here that will works on on old LB's, so the people that come to me generally want stuff fixed regardless of the cost. The dealers are beginning to shy away from the 2-cycles. It's a sad thing, so I have to keep the old machines going.

Anyway, here's the pictures. Be sure to look at the exhaust ports from inside the cylinder.


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Makes you wonder, doesn't it? There had to be some less than subtle hints that something wasn't right before things really let go.
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