Slipping Coupler?

[naturecoast1]

I have a MR228 in a 1980 Grady White. Just had the injured prop (and the spare) rebuilt after a soft grounding. Boat pulls strong from an idle, gets up on plane faster than I remember in the past. The problem is that I have lost some top end performance. The engine will now redline if you aren't careful, with either prop. And, I am only getting 23mph @ 5000rpm. Props are 15 1/4", one 17 and one 19 pitch. Acceleration is slightly better with one, as you would expect, as is top end speed.

My question is this: Is it reasonable to believe that the prop shop took some pitch out during the rebuild, causing the engine to overpower the props at high speed? Or, is this the correct symptom of a slipping engine coupler?

I don't have alot of I/O experience, so I am not sure exactly what a slipping coupler shows up as. Although, I cannot imagine a slipping rubber coupler that holds up, repeatedly, to a strong hole shot.

What do you think?

Thanks, again, for any help!

 

[Don S]

Re: Slipping Coupler?

What's an MR228?
A Mercruiser coupler if spun will smell like burned rubber and while you might see over 5000 rpm, you wouldn't be moving.
Best guess, the original prop was "Adjusted" but not remarked. So if it was rebuilt to original specs, you may be underpropped.

 

[naturecoast1]

Re: Slipping Coupler?

Thanks! No burning rubber, and the boat will still pull @5000 with more throttle, although I obviously can't go much. Will see if I can locate a 21 pitch prop and see what happens.

 

[MJ76]

Re: Slipping Coupler?

228 as in 305 Chevy? Another possibility is that the prop shop took a little diameter off at the grind. If the blades were all chewed up around the edges, I've seen some cases where, rather than welding all three blades, they'll just shave them down to clean it up, and sometimes put a heavier cup in to compensate.

Yeah, spun coupler wouldn't even get you on plane.