Discussion Starter · #1 ·
I just wanted to post my recent experience involving the engine overhaul of my 1979 Lawn Boy Supreme model 8238AE - self-propelled, electric start, rear bag - "top of the line." It was purchased new in 1978 (even though it is a 1979 model year - must have been one of the first produced). I was 12 years old when I "received" this mower and have loved it, used it and kept it for 34 years! Always well maintained and nourished with proper lawn boy oil in the fuel mixture, it started acting up last year. The mower was getting a little more fickle to start. After running for a while and then a stop - say to empty the grass bag, it was very difficult to start. Did the basics: carb overhaul, new ignition module, exhaust ports were clean, check the crankcase seals. Then finally two weeks ago, it just died and would not start for anything. I didn't do a compression test, but I suspected the rings were shot. A compression tester was around $35 and I figured I would put that into rings instead. I opened her up and found some piston damage - probably from a chunk of carbon (?) although the exhaust ports were always relatively clean and I kept them clean. The top ring was crunched down pinching the second ring in place. With the second ring not able to move, there was combustion blowout on that side of piston. Obviously no more compression for combustion. I put in part no. 92-4925 which was a new piston, rings, wrist pin, connecting rod, needles bearings; essentially everything needed change out connecting rod and piston. I changed the connecting rod because I couldn't get the old wrist pin out of the old piston due to carbon buildup, plus I figured the connecting rod was tired and why not change it all at this point. The crankshaft bearings were still perfect and I didn't change those out. My cylinder was perfect - no damage, no need to hone - just cleaned it with a light scotch brite pad. I cleaned up everything and reinstalled and put back together. She fired up on the first pull - fires up with just a touch of the electric start motor. Compression is noticeably better as you can hear the engine sucking in air from carb. when off and pulling the cord. I used Loctite 515 with primer per mechanics manual when putting crankcase back and let set 24 hours - longer than necessary. There is a Loctite 518 that is faster curing for aluminum which I found out about after the fact. Engine runs smooth and sounds great. She has many more years left! Yeah! Cause I dislike the new mowers and love the light-weight lawn boy 2 cycles! I wanted to share this in the event anyone is experiencing similar symptoms. I should have changed the rings years ago, probably - who knows. I also think the crankcase was leaking air - failed Loctite - over 30 years old - probably. Anyway, these old engines are fixable and worth it. Took me only a day to fix and all the new parts are still available online or e-bay.