B/S Engine Won't Crank

I have a Powercraft/MTD riding mower with a 18 HP B/S I/C twin cylinder engine mod 42A707 1238 01. I am at my wits end with this thing not turning over. It has always been hard to crank, or sluggish when cranking, but now it will not crank over practically at all. At first, I thought it was the battery, so I replaced the battery. Same thing. The starter would engage and roll the engine maybe a turn, then it would stop. So I thought it was the starter, so I replaced it. Same thing. So I thought it was the solenoid or the ignition switch. Prior to replacing these parts, I found a tip that instructed to jump straight from the battery to the starter to check to see if those parts were faulty. I jumped from the battery to the starter and the same thing happened. The starter gear would engage, but it was not able to turn the motor. So I tried to turn the engine manually by turning the crank and it was very hard to turn. I thought that it may be a compression problem so I pulled the spark plugs out and tried to turn it again, still very difficult to turn. It is not an OHV engine, so I have basically ruled out it being a valve problem. The starter is still not able to turn the motor. Even with the battery charger hooked directly to the starter it is unable to turn the motor. I can hear a buzzing sound that the starter is trying to turn, but just can't do it. I am curious at to what may be causing this. Could it be the transaxle belt (by the way it is a hydrostatic transaxle) putting too much strain on the motor. Should this belt be loose when the clutch is pushed in? If so, it is not loose when the clutch is pushed in, it is always tight. In fact I can not tell exactly what if anything this clutch is doing. Should I try to take both belts (the transaxle belt, and the mower belt) off and see if this helps? I have basically taken this thing all apart tracing down wiring and ignition problems, it wouldn't be too much trouble to take these belts off and see what happens. Could there be other reasons as to why this thing is hard to crank? Hooking the battery directly up to the starter should crank the motor right? if the battery is good? Please help I have spent a good week solid working on this thing now, and I do not want to quit until I get it running. I am out of ideas myself though.

 

Hmmm..is the engine full of oil? Sounds like the engine is locked up. The tranny belt could be a factor, depending on what you have, but on most MTDs, the tranny belt doesn't operate the same as on other mowers. MTD likes to use a varidrive belt system to keep from having to use transaxles with variable gear ratios.

 

After a week of trial and error, i decided to do something I have wanted to do for a long time. While, I didn't think they were a problem here, I have had lots of problems in the past with faulty safety switches (clutch, blade engage, seat, etc). I decided to rewire the electrical and take the safety switches out of the circuit all together. This was accomplished rather easily. Anyway, after rewiring, I tried to crank the motor to make sure I had everything connected properly and to my surprise it cranked easily, like it always should have. My only guess is that there was a faulty safety switch in the mix that was not allowing the current to pass through. I also cleaned up all of the ground contact points. Now it starts better than it ever has. Thanks to everyone for their help, I appreciate it. I was beginning to overthink the problem after having worked on it for so long.

 

If you could hear the starter buzzing then the safety circuit was not likely the culprit. They should only interrupt 12V to the small terminal on the solenoid which energizes it.
More likely a connection from the battery or solenoid or even the engine ground.
With electrical goblins, sometimes it matters not where they were hiding, just as long as they go away