What causes a spun prop hub?

[willxuout]

1996 Evinrude 225hp v6 Ocean Pro<br /><br />prop: OMC SS 15 x 17<br /><br />Was cruising offshore at about 30 mph when the rpm's shot up. Thought I lost the prop. Anyway, I got in the water to change the prop out with the spare I had. When I took the nut off I could see black rubber oozing out around the prop shaft. I took the prop off and there was melted black rubber all over the thrust plate and the hub was toast. The thrust plate was seized up on the prop shaft and I couldn't get it loose so I just put the spare prop on off we went.<br /><br />Does anyone know what could cause the rubber bushing to melt down?

 

[OBJ]

Re: What causes a spun prop hub?

Will....several things can cause a hub to spin.<br /><br />Hitting an object in the water.<br />Age....the rubber gets hard and brittle and slips.<br />Useage. The rubber is taking a lot of torque when in use. It finally gives up.<br /><br />The melting you experienced was caused from the friction of the spinning hub against the metal of the prop.

 

[wikelam]

Re: What causes a spun prop hub?

obj said it. numerous things can cause it

 

[willxuout]

Re: What causes a spun prop hub?

I took the spare prop off this afternoon and was able to free the thrust plate that was stuck to the prop shaft. The prop shaft surface where the thrust plate seats or meets the tapered surface on the shaft look pitted and scratched. This obviously happened when the shaft spun out at high rpm's.<br /><br />I'm buying a new prop, nut, cotter pin, nut and thrust plate washer. I'm going to re-hub the spun ss prop and use it for a spare. Will the surface gouges and pits on the prop shaft where the thrust plate seats something to be concerned about or will it function properly?<br /><br />Thanks.

 

[Solittle]

Re: What causes a spun prop hub?

Put a light coat of grease on the prop shaft when you install the prop. You should be OK.

 

[willxuout]

Re: What causes a spun prop hub?

Thanks,<br /><br />I ALWAYS put some of that blue marine grease on the splines and shaft before installing the prop. I use this boat exclusively in saltwater so I make sure I can get the prop off.<br /><br />Thanks again.

 

[OBJ]

Re: What causes a spun prop hub?

Will...if ya' find some small pits and stuff like that on the prop shaft, just take some emory paper and smooth them off. It'll be OK.

 

[willxuout]

Re: What causes a spun prop hub?

Thanks OBJ and SL<br />

 

[willxuout]

Re: What causes a spun prop hub?

I bought a stiletto 14.25x15 3blade Stainless Steel prop today. My original prop was an OMC 15x17 3blade. I was turning around 5500 rpm with the original prop WOT. I need to turn between 5800 - 6000 rpm WOT per Bombardier. The closer to 6000 the better.<br /><br />Do you think the new prop will be close to being the right prop? Once installed this new prop will be mine. NO EXCHANGES.<br /><br />Opinions welcome.

 

[OBJ]

Re: What causes a spun prop hub?

Will.....rule of thumb here....<br /><br />For every degree of pitch given or taken, add or take away 200 rpm to the existing rpm.<br /><br />So if you dropped 2 degrees in pitch, you will pick up about 400 rpm.<br /><br />A word of caution here....I hate to see engines run at max rpm, the operating range in your case should be around 5800rpm. Pushing the limit on these engines will help shorten their life. Just keep that in mind.

 

[willxuout]

Re: What causes a spun prop hub?

OBJ,<br /><br />I'll test the prop and post the results sometime this week.<br /><br />Thanks.

 

[willxuout]

Re: What causes a spun prop hub?

I wanted to update everyone on the new prop.<br /><br />I ran the boat today with four people and about 1/2 a tank of fuel (60 gallons). WOT was 5850 RPM. I didn't lose any speed. It ran 42.5 mph WOT. At 32MPH it ran about 4300 rpm. All looks good from here.<br /><br />Thanks again.