That doesn't sound too good. What you need to do is, pull the blade off, then remove the blade hub or adapter (small square piece the blade sits on) To remove that you will need to rest a large hammer or 2# sledge on it then whack the end of the sledge with another hammer as to spin the adapter off.
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Then pull the muffler off and check the exhaust ports through there. You can see the piston moving through the cylinder that way.
It sounds similar to when I threw a rod in one of my Lawnboys once. If anything it sounds like a bearing failure or something.

Before you get too far disecting your mower, be sure to check that the brake assembly or cabling isnt what is locking up the engine. A broken bracket or cable issue can cause no start due to the kill switch staying engaged all the time and if the brake was staying engaged could have caused the smell and lockup.

Just some ideas before you write it off since you stated clearly that the correct fuel mixture has always been used.

Thanks for your post indy452. I'm sure many will benefit by viewing your muffler removal procedure. My first check will be to view the piston's condition through the exhaust ports. I think you may be right about the bearing failure. In the meantime, I have put one of my other LawnBoy mowers into service. Good to have a couple of backup machines ready to go at this time of the year!

Thanks for responding fordtech. I will be sure to check the brake mechanism, along with brake cable and switch, especially considering the clinking sound in the flywheel/starter location, just prior to shutdown. Will advise cause of no-run condition when the problem is located.

Cool, I just made that suggestion as it happened to me once after recieving a mower I purchased on Ebay. I thought the coil was bad because I had no fire and found that the brake assembly was broken and forced it to be in shut off mode all the time. I had to replace the mounting bracket assembly to fix it. I figure something similar may have happened to yours considering the description of circumstances and the fact that you have always used correct fuel mixtures. It should run essentially forever with correct mixture.

I finally viewed the piston via the open exhaust ports and found much play and side to side movement of the piston within the cylinder. I don't recall seeing this in any of my other working Lawn-Boys, so I suspect severe damage to either the cylinder sleeve/liner or the piston.

I replaced engine shaft seals and I swapped the carburetor and ignition pack and spark plug with known good replacements and still experiencing the same problem...Engine starts only when completely cold for 5 seconds and dies. Attempts to restart leave wet/raw gas on the spark plug. Spark checks out OK, so I suspect the side to side play of the piston as the cause of problem.

I also checked the braking mechanism and on/off contacts and it is working normally.

Please advise if any of you folks have experienced this problem and if it may be due to the piston with much side to side movement within the cylinder. Thanks for your help.

I may have the same model lawnboy, ie if self-propelled. I just blew my engine also. It locked up on restart, ran fine until then. Checked flywheel brake and it was ok - so I dissasembled. The rod was broke and the rod end was gone off the crank. Also the crankshaft has worn a hole in the bottom crankcsse. Looks like about 1/2 inch vertical play in crankshaft. Maybe too much play so rod disintegrated. Plenty oil in crankcase. I don't feel too bad however as I paid $25 for it 3 years ago.

bigal mo:

Before disassembly, were you able to break the engine loose, so it would rotate freely or was it locked up until disassembly? I was able to get my engine to break free, but I suspect compression is now reduced, causing the no-run condition. I guess I'll need to fully disassemble mine to determine the exact part(s) that failed. Will advise once it is open for inspection.

My other two Lawn-Boys will take over lawn mowing duty at this time.

Yes, it did break loose but then it just free wheeled as the piston was not moving. I went looking on Craig's List for a replacement motor. Found a 10422 that I bought. But now I'm in a quandry as the 10422 is like brand new so hate to pull the engine. But what a tank the 10422 is. It is not self propelled. The 10422 has the new larger deck which makes it a lot larger and heavier and harder to push.

bigal mo:

Thanks for the information, especially about the heavy deck Model 10422. I almost purchased one of those used, but suspected it was very heavy, due to the increased size and longer wheelbase. I was glad to see the return of the older, push-type cast aluminum deck when the DuraForce Engine was introduced.