Should an engine coupler go out in two years? What could cause this?

[neillibson]

I had my 120 hp mercruiser i/o coupler replaced a few years ago and have only used the boat about 5 hours total and now the rpm's increase while the boat speed decreases under acceleration. At low speeds it seems to operate fine. I checked the prop and it seems fine. What could cause this "slippage"?

[Bubba1235]

Two possibilities, prop or coupler. I suspect what when the coupler was replaced it was not aligned properly.

[Home Cookin']

I can't speak to I/O's but sounds like your prop is spun. I'd switch props to test (you can sometimes tell by looking if they are spun) or take the prop to a prop shop if that's easier.

And I'd also recommend using the boat more!

[tpenfield]

Yes, the 2 high probability things are coupler and propeller hub.

Improper engine alignment can fatigue a coupler. 5 hours of use sounds pretty dramatic.

Hopefully it is the prop, as that is an easier, less costly fix.

[mr 88]

In most cases when a coupler goes it is the splines and they are either good or bad,no in between.There is a very small possibility that the rubber in the coupler is spun,which I have never seen, I agree with the post that say check your prop.Maybe try your backup or mark the hub in two places and see if it moves.

[Thalasso]

To see if you have prop slip, take a marker and place a line straight through the center of hub lining up the hub with the prop.. Take your boat for a ride aqnd when you pull it out, see where the lines are. I f the lines are not lined up you know you have prop slip.

[kiethco]

I just spent 2k to find out my stringer was sagging and causing coupler failure. I had a 1978 Carlson.

[Fordiesel69]

Even if you had a bad transom and bad stringers, you would not spin a coupler in 5 hrs if it was aligned properly. It would need to be severely out of alignment. I bet it is a spun prop. If you had a v8, then yes you would have the power to spin a coupler out in a matter of no time.

[Pete104]

$2000? To change a coupler?