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Can a 9.5 Sportwin spin a prop?

S

Sam110

Regular Contributor
Well going from one thing to the next with this '71 9.5 Sportwin.

Took it out on the river this afternoon to 'gloat' over how well it now runs after fighting with that "filler plug" carb issue. (previous post) All seemed well even though I seem to have a bad exhaust boot seal as I had to take the engine cover off to get to 'top end'. It ran fine up and down the river at various speeds (cover off) and would purr along at idle and get up to plane in no time. I had been on the water for about an hour and throttled up for another "blazing" pass down river and it just wouldn't get up to 'plane'. The engine would rev up but no power/speed. I backed off and it would motor along fine. I tried this several times with the same result before I remembered reading thread talking about a "spun prop" but that was on a much larger engine. Could it be the same thing was happening to my little 9.5? Seemed so. I took no further chances and headed back to the dock before I lost ALL forward motion.

Is a spun prop likely my problem even though the prop is a new one?
Is there a source for a new exhaust seal any one knows of? Marine Engine shows they are unavailable.


Sam
 
a buddy of mine has the same motor and had the same problem with his prop. remove the prop and im willing to bet the center is broken away from prop.
 
With a magic marker, make a line on the hub into the aluminum prop. Take the rig for a run and duplicate the problem. Now, take a look at the line you drew.... if they are no longer lined up, the hub has spun.
 
Well I'll never hit the Power Ball, but with the luck I have those two marks would end up lining back up! Can't I replicate this issue on dry land? lol
 
Sam110 said:
Well I'll never hit the Power Ball, but with the luck I have those two marks would end up lining back up! Can't I replicate this issue on dry land? lol
Click to expand...

You could block the propeller from turning with a piece of wood after putting the engine in gear, then with a breaker bar and socket see if you can turn the flywheel.
 
You don't want to do that. Putting a breaker bar with a socket on it on the flywheel nut can screw up the torque for the flywheel on the crankshaft. Best way is to take it back to the lake.
 
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True kim "IT TAKES A NICKLE TO GO FIRST CLASS!" lol Live and learn. The prop is a SOLAS, new in May of this year and hardly run. For another 200 nickles I could have bought a MICHIGAN MATCH. But does that mean that an OEM prop is twice as good as the MICHIGAN or a SOLAS? Mmmm....I doubt it. . . but then again the OEM was still working, just bent up a bit so I "upgraded" . . . right out of the water!
 
Trouble with a dry land test is, the prop hub has to hold enough to hold back 9 and a half snorting horses. How much torque on the flywheel is equal to 9 horses (+ another pony) at the prop shaft? Actually, OMC did at one time make a test fixture that could be used with a torque wrench. The one I had was not practical.
 
Gator I discovered your very point! I removed the prop and acquired a piece of steel rod the size of the prop shaft and drilled a hole in it to insert a "shier pin" replicating the prop shaft. I clamped it in a vice, slipped the prop down over the "shier pin" notches and attempted to turn the prop blades loose from the hub. Couldn't do it, so I used a marker and followed Joe's suggestion and will have to go back to the river and see if I can replicate the problem. I'm guessing the lubrication and chill of the water may have some to do with it slipping while on the motor. I'll see how that goes and post the outcome.
 
Sam110 said:
Well I'll never hit the Power Ball, but with the luck I have those two marks would end up lining back up! Can't I replicate this issue on dry land? lol
Click to expand...

I doubled my odds Joe and put marks on the inside and outside . . . just in case! lol
 
Made it back to the river today with an 'experienced' boat pilot to evaluate the engine / prop issue. Well, I'm pleased, yet somewhat 'red faced':eek:that the boat ran fine no "slippage" of any kind. He theorized what had happened was that the prop had experienced a "VENTING" issue with some sort of debris from the water around the lower leg allowing the prop to draw in air (venting) resulting in a loss of propulsion under higher RPM.

SO I've learned a little something I wasn't aware of about boating . . . and trouble shooting through the internet . . . even the best of boat mechanics can't help if they don't have all the information. Thanks all.
 
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