spun prop?

[adamkat22]

i have an 80's 85 hp force outboard. recently it hasn't been going as fast as it was earlier in the season. can hardly get on plane with one person in it, and definitely can't with more than one person in it. it works just fine at low speeds though. i pulled the prop off today and marked along that spline coupler with a grease pen, then stuck it back on, put the outboard in gear (reverse), and spun the prop by hand. it spins freely in one direction, and i can (with some effort) spin it in the opposite direction as well. when going opposite, it almost sounds like there is air building up in the lower unit, then the air releases, and the prop turn a quarter turn. maybe this is just the sound of the motor turning over? is it supposed to do that? i did this a few times, but the grease mark stays in line. new to working on this, so any thoughts/help on what to look for next would be greatly appreciated! thanks. unclear if i am trying to diagnose a spun prop or some other issue....

 

[alldodge]

recently it hasn't been going as fast as it was earlier in the season. can hardly get on plane with one person in it,

Do a compression test. My thought is you need some head work

 

[Texasmark]

I assume that model of the Chrysler/Force has the geartrain setup like Mercury in that F contains an overrun clutch for times when you are at some speed and cut the throttle...allowing the engine to slow but the prop to follow the rotational pressure caused by the water passing over it at the current speed.

With that said, think of the blade of a hand saw. you have a triangle geometry where you have a steep vertical edge to the tooth and then a ramp back down. The steep vertical is encountered when you try to rotate the prop CW. To turn CCW requires the crankshaft to turn CCW also...The F gear is driven by the vertical edge.
Rotating the prop CW, you are on the ramp and the prop shaft will turn up the ramp and then fall back off the vertical edge and make a clicking noise in the process.

A spun prop means that the splined Brass/Bronze center hole does not turn in sync with the aluminum/SS outer shell. If you marked all the way from the Brass to the outer shell material and testing did not cause the line to change, then you don't have a spun prop.

 

[Sea Rider]

A hub slip test must be done on water and checked soon after a wot run, not with hand on land...

Happy Boating​