Starter pinion not staying engaged

[swedish-fish]

Hello all.
I've recently discovered that when I start my 155D, the starter won't stay engaged with the engine more than a revolution or two of the engine. Even if I pull the decompression lever and thumb the starter, I can hear the pinion gear disengaging and and spinning free after a second. Fortunately, restoring compression with the lever and cranking, the one or two revolutions are enough to start the engine. There seems to be plenty of power to spin the engine. My concern is that with cold weather comming, I'm going to have to fix this. Anyone have any ideas as to what's wrong?

My first thought was a weak battery. I've since replaced the battery and the starter behaves the same.

Next, I've ordered a soleniod. We'll see if that fixes it.

 

[choffman41]

Never had a Yanmar starter off before, but would assume they use something similar to a Bendix drive which is where I'd be looking.

 

[swedish-fish]

As always... I get an education when I work on this tractor. Now for the benefit of others I'll post my findings.

Confirmed, it was a bad solenoid. The solenoid drives an arm that overcomes a spring and pushes the pinion gear to mesh with the gear on the engine flywheel and holds it there as long as the key is turned. Thanks Gary Jamieson for the diagnosis and fast shipping of parts as always!

The one problem I had was when I wired it up the battery contact sparked when I reconnected the battery. That should have been a tip off... Then nothing happened when I turned the key and I noticed the solenoid getting warm. I disconnected the battery and wondered what was going on...

...Come to find out, the after market solenoid had the opposite post tied to the ground side of the coil. See picture #4 reverse polarity. Hopefully I didn't burn anything up. Since I reversed the cables on the posts. It starts great now. Hope this helps others avoid what I did wiring up a short.