Toasted ring gear?

I had a nasty little problem on a 400D this last weekend... I was giving my dad a tractor driving lesson, and things were going alone fine when the tractor suddenly started loosing power. After a few seconds of really struggling, the engine stopped and I noticed smoke coming out of the starter.

I pulled the starter, opened it up, and it's definitely burned out. I noticed also that the battery was dead, and I found that the teeth on the ring gear look mighty worn. My theory is that the key switch stayed in the START position -- it's really hard to tell where it is. That kept the starter engaged, leading to the burn out a few minutes later, and the current draw drained the battery. And, since the bendix gear was still engaged on the ring gear, when the starter froze up, it stopped the flywheel. Sound legit?

I was able to pull start the tractor later, and it ran just fine otherwise, so the engine is ok. Whew...for a second there I thought I had seized something.

In any case, I'm looking some advice on the ring gear. I've attached a picture of it below. Prior to this incident, the starter would occasionally spin, so I know there was some wear on the teeth already...I just don't know how much. Do you think I can get away with flipping the ring gear over, or do I need to replace it completely? I think it's bad enough that I need to split the tractor and fix it one way or the other. Any expert opinions out there?

Many thanks,

- David

• Ring gear pic

The 400D is back in working order! I took a file to some of the ring gear teeth to smooth out any ragged edges, then I put back in the rebuilt starter. It turned over just fine, and ran just great. 20 minutes later we used the tractor to haul an old dead tree out of a ditch. Good to go, and I didn't need to split it!

Thanks to everyone for their advice.

- David

I suggest that if you go to the trouble to split the tractor and the expense of a different starter, flip the gear. That way everything is new or like new again.

Wow...that's an astute observation. Lemme see if I follow: on a four cyclinder engine, the pistons are moving in pairs...the pair moving downward would be in the power stroke and intake stroke, while the pair moving upward would be in the exhaust stroke and the compression stroke. Ah...think I just got it. Without an ignition spark to get the power stoke going, you'll have one of the cyclinders on its compression stroke. At some point during the compression, the flywheel won't have enough inertia to overcome the compression. That compression point should be roughly the same for each cylinder, with two pairs of pistons, that's 360 degrees / 2 = 180. Did I get that right?

And, I was going to say that the stopping point would depend on where in the rotation the ignition was killed, but the ignition isn't a constant force...it only applies during two very short periods on each rotation. So it doesn't really matter if the ignition kill happens at TDC immediately after the spark or when the piston is halfway down the cyclinder...the force has already been applied to the piston.

Just thinking out loud...helps me get it all straight. Did I pass the physics test?

Thanks,

- David

Boy! I 'taint smart enought to know why it happens, just have noticed those "patterns" over the years.

When that starter smacks the flywheel, chances are it is hitting in the same spot time after time after time. It's a wonder they last as long as they do.

Another thing I've always wondered about is the "bendix' type starters. They are spinning almost full bore when they hit that flywheel. How do those teeth and the sprags manage to take the punishment?

WIth a solenoid type starter on the other hand, the drive is fully engaged with the flywheel teeth before the starter ever begins to spin.

Dunno,

Allan

Sharp eye.

Likewise, an 8 cylinder will normally land in one of 3 spots on the flywheel.

Not many folks notice this little “quirk” of internal combustion engines.

However, I think if I went to all the trouble of splitting the tractor, I'd just go ahead and replace the flywheel.

Allan

Great! I think I'll try that first...if I can stay away from splitting it, I can save myself a lot of trouble. It's a couple of hours away from all my tools.

- David