Starter just whirrs sometimes

My Samurai's starter has now done this 3 times in the last couple weeks - sometimes I swing the key and the starter just whirrs away freely, as if the bendix drive isn't engaging, but we know from the way these things are wired up that's not possible. I understand starters also have some kind of one-way clutch mechanism in the "gearbox," could that be what's causing it?

Your solenoid is mainly an electromagnet. When 12 volts are applied, it pulls a lever that sends the Bendix toward the flywheel. If there is a bad connection in this electromagnet area, then no pulling against the return spring.

The other function of a solenoid is to be a switch. Small amperage to the small post (from an ignition switch) allows big amperage (from the battery) to flow to the starter motor.

Sounds like your solenoid is doing one of it's functions and not the other. If this starter is a typical GM starter, then rebuild or replace the solenoid. If it is a Ford style with no round solenoid (just a hump), replace the starter.

If you like to mess around, disassemble the solenoid and clean the internal contact points with emery paper. Reassemble and see if that fixes it.

Oh yeah, make sure you have 12 volts coming from your starter, and lots of amps. Good connections, too (at both ends of both cables), so you don't lose current doe to corrosion. Do this part first.

always the possibility of a bad spot in the ring gear.

Also don't forget to check the big ground line from the battery to the block.

iceracer wrote: always the possibility of a bad spot in the ring gear.

That's got my vote for most likely.

If you haven't had any grinding prior to this problem I would rule out ring gear as the problem. It's possible teeth broke off, but not likely.

Sounds like the bendix is sticking.

Not uncommon, especially in older vehicles, or those operated in very cold conditions. Old or cold grease can keep the gear from operating correctly letting the starter freewheel.

I'd start with pulling the starter and cleaning and inspecting the gear and lever that pushes it out to engage the flywheel. Also clean and regrease the gear mechanism to prevent sticking.

With the starter out you can use you jumper cables or a battery charger to operate the starter and check that the gear get pushed out fully.

There are basically two types of starter. One I call the "inertia" starter. Think older Fords or anything that had a separate solenoid.
Most today, as "Kramer" noted the solenoid does two things. I engages the gear at about the time it engages the motor. The drive, being one way, can be bad.

Thanks all. The flywheel and ring gear on a Samurai are exposed to the outside world under the engine, so some teeth could be broken off easier than on most cars. Sticking bendix sounds like another strong possibility.

In reply to GameboyRMH:

I think you're missing parts if you see exposed flywheel on anything built after WW2.

^That's kind of what I said the first time I saw it, but I've been assured they leave the factory this way. This pic is looking from the engine towards the rear of the car (not my own Sammy):

Looks like the sheet metal inspection shield is missing in the photo.

You can see the bolt holes in the photo.

Edited for minor typos

Looks like you're right, I did some searching and found this:

I wonder why so many sammy owners don't know about this part?

(Or why pretty much none of the sammies driving around have one?)

Between lazy clutch jobs and the serious off road folks having trouble with it getting filled with water(proper fix is to drill a hole) a lot probably are missing.