Starter not engaging engine

[scott r bishop]

Trying to nail down a starting issue with a friend's boat so we can get it out before winter; 1988 4.3L MerCruiser and the starter is spinning at high RPM but isn't turning over the motor. 

● Put in a new battery and checked that we're getting plenty of amps to the starter motor
● Removed the starter motor and had a pro re-builder verify that everything is working on it, and that the pinion is moving out and stays out even under a load
● Greased all the contact surfaces in the starter motor before re-installing it. The pinion teeth are good, and it moves out with just finger pressure
● All the electrical connections and the bolts holding the starter motor on are tight.  There are no shims between the starter motor and the engine block (some have said to try this?)
● Used a ratchet to rotate the crankshaft, to be certain that we have good teeth available on the starter gear.  Still no luck

My guess is that one of the gurus on here has run into something like this before, I'm just out of ideas.  Any help is greatly appreciated!

Thanks,

-Scott

[Rich_V174SS]

Sounds like a stripped pinion in the starter. The solenoid is kicking it out to make contact with the flywheel but the gear is not spinning, just the shaft. When tested off the engine it will spin like normal because there's no load on the pinion gear.

[scott r bishop]

Thanks for the reply, Rich. 

We took the starter motor apart, and there are three little nylon gears that orbit inside a planetary gear.  The electrical stater shaft gear meshes where these three little gears come together at the center.  All of those teeth looked good; on the shaft, the pinions, and the planetary gear.  Are you referring to a different gearing in the starter motor assembly?  I couldn’t disassemble the starter motor further than to take out and grease the three little gears...

[Jason]

Maybe the pinion comes out but then comes back in for some crazy reason once it hits the flywheel. I guess I'd try a different starter to rule that out. I really don't see what else it could be. Flywheel loose??

[75starflight]

Just a thought... In my line of work I have seen starters test  perfect on the test bench(all specs right on the money) the starter gets installed back on the piece of equipment it came off of and then fails to work properly. Install a new starter on the equipment and wam bam thank you ma'am it starts.

As Jason said try a new starter.

[Plugcheck]

Difficult to do with an installed Marine engine, but I would check the opinion engagement.  Could the pinion be the correct size?  Too close or far away from the flywheel.  Easiest recommendation would be to try a new starter.

[Maclin]

Is this a new to you boat and it has always acted like this?

If so...
Not correct starter/bendix/pinion shaft or pinion monted wrong or pinion spinning on shaft
Starter shimmed too far away not letting pinion engage
Starter flange not correct or problems at bell housing preventing proper mounting


If it was ok at one time then revisit the most recent maintenance touches.

[Retro Performance]

Im with Jason and 75 Starflite.....I would remove the starter.....look at the flywheel.....if the ring gear is still on it, it must be the starter? 

[scott r bishop]

Thank you all very much for your replies - sounds like we'll just replace it and be done with it.  It's always good to hear it from the pros before giving up on a repair, but that's the best course of action here (especially given how hard it is to access).