Merc 7.4 starter just spins...

[Mischief Managed]

Engine is a 2000 7.4 MPI with around 250 hours.

Here's what happened.

Docked the boat to get ice cream after a full day of boating.

30 minutes later I tried to start the boat and the starter turned the engine over a little then stopped. Kind of sounded like a dead battery.

I switched to the other battery and tried to start the engine again. This time it turned over strongly but briefly as came to a grinding/clanking halt before the engine ever fired. Now the starter just spins without engaging.

Any ideas? I'm thinking maybe I had hydraulic lock and may now have a broken starter and/or broken teeth on the flywheel. Gonna pull the exhaust maniflds and starter tomorrow.

 

[Don S]

Re: Merc 7.4 starter just spins...

Pulling the starter and looking is about all you can do. But pull all the spark plugs and crank the engine over by hand and make sure there isn't water in the cylinders. No way do you need water sitting in the cylinders while you play with the starter.

 

[Mischief Managed]

Re: Merc 7.4 starter just spins...

Man, that was quick. Thanks for the speedy reply. I figured I'd know nothing until I pulled the starter. I will pull the plugs and check for water too. Thanks for that.

 

[Mischief Managed]

Re: Merc 7.4 starter just spins...

So I was looking at the parts section of iboats and discovered that my engine takes a reduction gear starter. This makes me more hopeful that it's simply a starter issue because if it was hydraulicly locked, it probably would not have turned over the second time. Do these reduction gears fail much? Fingers are crossed.

 

[Don S]

Re: Merc 7.4 starter just spins...

Do these reduction gears fail much?

They don't fail any more or less than the older type starters.
You still have to check for water before it kills your engine.

 

[Mischief Managed]

Re: Merc 7.4 starter just spins...

Got the water out and found my exhaust shutters were MIA. Starter is on my bench awaiting failure mode analysis. Flywheel is fine.
Thanks for the help. Hope I did not bend a rod...

 

[Mischief Managed]

Re: Merc 7.4 starter just spins...

Took the starter apart. Found that the stationary ring gear that surrounds the three planetary gears in the reduction gear section of the starter had missing teeth by each planetary gear. It's made of plastic. Perhaps it's designed to fail to prevent worse damage??? I plan to put a new starter in ($152), and see if I can repair this one later. The rest of the starter seems fine. Thanks again for all the advice!

Part number 9, above, is what failed.