Help with an L X-172 John Deere engine problem.

I have a John Deere L X 172 mower with the 14 hp Kawasaki engine.I bought this mower from a guy whose mother had it and when she passed away it was his. A little history first.He did most of the mowing with this machine for his mother. He said one day his son was doing it and came to tell him the mower stopped and the motor was still running. He went to see about it and saw the pto clutch and drive pulley lying on the ground. They pushed into the building on the place. He then started using his ZTR mower and did not spend any time on this one. I was in the building with him looking at something and saw the mower just sitting there. I mentioned that I needed a deck that size.He said he would sell the mower, but not the deck separately. He offered me a good deal, so it went home with me. When I looked at the problem the bolt that holds the clutch and pulleys onto the crankshaft was broken just above the thread on the bolt and part of it was still in the crankshaft.That allowed it all to fall off. I pulled the engine extracted the broken end of the bolt. i went to the local Deere dealer and bought the correct bolt and the thick washer for the bolt head end. I got the broken end out with out damaging the threads in the crankshaft. I cleaned and prime the bolt and crankshaft threads with Loctite primer and then applied Loctite as per the John Deere manual. The bolt was torqued to John Deere specs and then the engine was reinstalled. It worked well all last summer and fall during mowing season. This past week I got it out to do some mowing and after about 30 minutes the pto clutch unit falls off again just like before and the bolt broke in the same place. I have worked on and around small engines for more than 50 years even owned a small engine repair shop for a while. I have never seen this happen before and certainly are baffled by an exact repeat of it . Does any body have any suggestion for this, Were there any TSB on this published by Deere? The local dealer has no idea. The dealership has just changed from a individual ownership for the last 50+ years to being bought by a large chain of dealerships and the first thing they did was get rid of all the good help.Some retired,some left on their own then some got pink slips. They have one or two infidels called mechanics there now ,but they know nothing. I asked one about it and he just gave me a blank look and said he didn't work on small stuff like mowers. I hate to replace the bolt and not find some cause and cure for it. Thanks in advance for your help.

Gene Davis Tennille, Ga.

I ASSUME the LONG square "key" that extends from the washer upward through the clutch into the traction drive pulley is present and in good condition, and the keyways are too?

I have seen this a few times as i am john deere tech. I would make sure the crank and key way are in good condition.I had one break a bolt twice before realizing the key way was wollered out. Once those clutches fall off i felt like it damaged them. You may have to replace the clutch.

Thanks for the help. I'll check this .Gene Davis

I'd maybe try another source for that bolt ? Maybe Deere got a bad batch ?
I had an LX172 for several years I bought it used and it was a fine little machine. Only problem mine had was the steering shaft bushings wore because previous owner didn't keep the front spindle greased.