permanent magnet gear reduction starter.

Thank you O.G.O.:wizard:

^^^^ that is correct above about PMGR.

Mercruiser for the longest time has use Delco PG260 and Delco PG260FI Starters.

It is recommended to torque the starter bolts to 30 ft lbs if all possible. Also the correct bolts need to be used per what the starter app is.

These starters require min of 10.6 V at cranking. You need to check across the starter to what your voltage is cranking and not cranking.

Also is the starter lined up correctly and mesh evenly with the flywheel teeth ? Mark it with some marking compound on the starter teeth so you can see the next time or test it to see and pull the starter.. Possible the starter needs to be shimmed

Also possible flywheel problem - missing teeth or bent ?

Possible slight hydrolock of the engine - any water droplets on the spark plugs or rust ?

What is the compression ratio of the engine ?

Mercruiser really recommends not cranking the starter over for more than 10 seconds - they list up to 15 seconds at any one giving time. IMO 10 seconds is the max I would crank the starter over before giving a rest for a tad bit; then hit it again

forgot to add - buy a more quality starter - those 50 to 75 dollar starters can only last a couple of engines starts to maybe up to a year. A cheap knock off starter might be great for a a 135 hp 4 banger or even a V-6 merc low compression engine .just saying.