Prop slipping.

[fbriggs]

Ok where to start, first info
Merc, 2001 2 stroke, 3 cyl eng. Model# 50ELPTO, Sn# OT182471.
Purchased motor heard it run off water on muffs, idle smooth good water flow out pee hole, shifted in and out of gear fine.
Took home installed on boat, took out to lake lowered motor opened throttle would barely move but engine reved up, right away thought prop hub bad. Pulled out looked at prop hub bushing looked a little suspecious so ordered a new hub. Back to lake same thing. Now no noise out of gear case like a shifting or gear problem so didn't know exactly what was happening. Before pulling gear case put into both Pulledfirward and Rev and grabbed prop could turn motor over with plugs in. So pulled lower unit to inspect all gears and spline shafts everything looks good to me, had some signs of rounded edge in dog and gears but nothing that looked bad enough to cause problem plus no noise like you would hear if gears weren't engaging correctly. Only thing I noticed was top spline on drive shaft had a twist to them like someone hit something pretty hard but that too would no cause problem I was having. Oh forgot to mention prop is a 11 3/4 x 10 alum 3 blade.
One more thing when engine would rev up and slip water would stop coming out and once at idle or you shut off and restart good stream of water. Water impeller like new key good and installed the correct rotation.
I have been a mechanic all my life and have worked on numerous motors of all kinds, overhauled motors, gas, diesel, LP, electric, 2 cycle and 4 stroke, and all makes of gearcases this really has me stumped. Any suggestions will really be appreciated. I evidently am missing something here.
Thanks

 

[racerone]

Somebody hit something.----Take lower unit apart for full inspection.----This sounds expensive !

 

[Faztbullet]

Driveshaft snapped at pinion gear....

 

[fbriggs]

Pulled lower unit completely disassembled. Someone did at one time hit something top splines of shaft show slight twist. But all splines, shafts, gears, clutch perfect condition. No debris at all, pulled power head, inspected crankshaft splines perfect condition. Just for kicks pulled crank did find #2 piston scored so if going to keep engine will overhaul and reinstall. Problem did not find one thing that explains the slippage issue.
Only other thing I can think of is cavitaion issue with prop? Motor is a 20" shaft on s 20" transom. Prop is a Michigan wheel 11 3/4 x 10 think way to small for my boat but don't know much about cavitaion issues. May just overhaul motor put back on change prop and see what happens. Did find good complete lower for around $700.00 if needed. Or sell completely overhauled engine, and rest of parts on e-bay and start over.
Amy other suggestions would be appreciated.
Thanks

 

[Silvertip]

Unless this engine is a "Big Foot", the gearcase has a 1.83:1 ratio and as a result runs a small diameter prop. If it is a Big Foot, it has the same gearcase as the 75 - 90 HP triples and is a 2.33:1 gear ratio so 13 - 14 inch props can be used. You should not be experiencing prop blowout with that prop. If you can spin the prop by hand with the shifter in reverse or forward either the shift cable is misadjusted or something is broken in the driveline.