JD LT160 engine not turning over freely
I'd be interested in any opinions on the following. The Mower is a 2002 JD LT160, with Kohler Command 16hp (CV460) motor at about 375 total hours. It has been run a couple of times since its winter lay-up, with no issues as usual. Last week I went to start it and it would try to turn over the motor but only managed to turn it a small part of one revolution (based on watching the screen on top of the iengine). Sounded like low battery power, so I hooked up a good battery, with same result. Got meter and both batteries measured fully charged - tractor battery is standard small unit, 2 years old, but the jumper was a group 27 bruiser, fully charged, Next, I jumped the starter, around the solenoid, with same result - not enough juice to spin it over. I pulled the spark plug, and it then spins great so cylinder not full of fuel, etc. and hydro-locking. Plug back in and no spin again. Finally, I put the plug only partly in, leaving it quite loose, plugged in wire, and hit key. It spun and fired fine, with the loose plug allowing blow-by. After a couple of minutes, I tightened plug properly, and it started again just fine and has continued to start properly since. My conclusion is that it had a problem with the compression release mechanics getting hung up in some way. Unfortunately, I know nothing about how that release system works, or if there are other potential sources of the problem. Any maintenance I should do to prevent this again? This is an OHV design with hydraulic lifters, I believe, and it has never had any service like valve adjustments. All thoughts much appreciated.