Mercury 9.9 Prop Slipping - Strange

[Chris in Indiana]

Well, once again I need the help of the brain trust here on iboats.com.
I'm living in Monterrey Mexico for two years and I brought my inflatable Achilles with me, and a Johnson 9.5 which died as soon as I got here. The replacement is a new-to-me 1989 Merc 9.9 that runs wonderfully after a carb cleaning and new water pump. Today was my first time out with it and everything was great for about an hour. Then all of a sudden the prop started to slip big time. Anything more than idle speed (in gear) would result in the motor reving up and no power at all. I was accross a huge lake when it started and by the time I limped home it gave out completely and I rowed the last 1/2 mile or so. Reverse didn't work either. Strange thing is that I NEVER heard gear grinding or anything to indicate that I stripped some teeth somewhere. I don't have a manual yet (should be here in 3 - 6 weeks with the Mexican mail system - grumble grumble) but I do have a detailed parts book. In the break away view there is a clutch shown in the lower unit, part number 43217. Could this be the culprit? I have not yet checked the lube level or quality in the lower unit - to tired from rowing. I have researched the prior posts and noticed that some motors/props have a rubber component that can shear. Is there such a thing on 9.9's? No way I'm that lucky!
Thanks in advance!!

 

[Karl_Childers]

Re: Mercury 9.9 Prop Slipping - Strange

I am not all that familliar with a merc 9.9 but it sounds like the symptoms of a spun hub. If you have a splined prop shaft, and the propeller smells like burned rubber, replace the prop. Test by putting the engine in gear, and try to rotate the prop. It should be intuitive at this point if you indeed have a spun hub. the prop will not spin without spinning the flywheel, your problem is elsewhere. By the way, remove the spark plug for this test. It is highly unlikely, but possible for the engine to fire while you are spinning the prop.

If you do not have a spun hub, pull the drain plug on the gearcase and inspect the magnetic drain plug for excess metal shavings. Let us know what you find. I just thought that you might have a shear pin on that prop. Pull the prop and look at the backside for a shearpin, let us know what you find.


Did you hit something before the trouble began?

Rob

 

[Chris in Indiana]

Re: Mercury 9.9 Prop Slipping - Strange

Karl,
Muchas gracias! After a few cervezas and a couple hours of rest I mustered the strength to check things out. It's amazing how punishing rowing can be, especially when I'm so out of shape.
I pulled the prop and you were dead on, I noticed a burning rubber smell before I even got it off. Indeed when I removed the prop the inner splined tube remained on the shaft and was covered with balled up black goo. This is the newest motor I have ever had and the first to have such a feature. Gotta say I'm just elated to NOT have smoked the lower unit.
Incidentally this was my first run with this motor, but the prop is significantly worn at the leading edge so my guess is that it was either toast when I bought it or very close to the breaking point.
So, is the only option now to buy a new prop? I looked over the mating surfaces pretty close and there does not seem to be any press-in components that can be easily replaced.

 

[Karl_Childers]

Re: Mercury 9.9 Prop Slipping - Strange

Props can be repaired, but for a 9.9 it's not worth it monitarily. Glad I could help

 

[CharlieB]

Re: Mercury 9.9 Prop Slipping - Strange

That black goo is what is left of the heavy rubber that was molded onto the splined collar, then the 'hub' was pressed into the prop.

If the blades are not hurt too bad a prop shop can press a new hub into your prop.

You may want to get an estimate and compare that to the price of a new prop.

It NEVER hurts to have a spare.