Incorrect prop?

[rdrainville]

I picked up this old rib cheap. I'm almost done getting everything together. The prop that was on it looks wrong. But just to be safe, I want to make sure it couldn't be something else. I'll post pictures of the prop but it's a big gap between the prop and the housing on the lower unit. I didn't measure the size of the gap but it's maybe an inch or a little more. I did measure the length of the shaft that was sticking out of the lower to be 5.5". It looks like the prop just isn't long enough. The only markings on the prop are m6 475 and a couple letters I can't make out. I can tighten the nut down enough to put the pin in.

 

[Scott Danforth]

Something not right

 

[jimmbo]

First guess is that prop is for a Motor with a Smaller Gearcase
Second guess, is that there is more than one Thrust Washer on the Propshaft

Exactly what motor is involved here?

 

[rdrainville]

First guess is that prop is for a Motor with a Smaller Gearcase
Second guess, is that there is more than one Thrust Washer on the Propshaft

Exactly what motor is involved here?

It's a 48 spl. I thought Maybe it was a prop from a mercury or something, I heard they have a shorter shaft.

 

[rdrainville]

First guess is that prop is for a Motor with a Smaller Gearcase
Second guess, is that there is more than one Thrust Washer on the Propshaft

Exactly what motor is involved here?

Also, there's only one thrust washer, even without the thrust washer, the prop won't slide all the way on.

 

[flyingscott]

Does that prop have a removable hub?

 

[racerone]

Prop in first picture appears to have a bad hub.------Those numbers are not factory and they mean nothing.

 

[flashback]

That prop is shot.

 

[QBhoy]

I picked up this old rib cheap. I'm almost done getting everything together. The prop that was on it looks wrong. But just to be safe, I want to make sure it couldn't be something else. I'll post pictures of the prop but it's a big gap between the prop and the housing on the lower unit. I didn't measure the size of the gap but it's maybe an inch or a little more. I did measure the length of the shaft that was sticking out of the lower to be 5.5". It looks like the prop just isn't long enough. The only markings on the prop are m6 475 and a couple letters I can't make out. I can tighten the nut down enough to put the pin in.

I’d say to count the splines on the shaft and then the ones on the prop. If they are different, that’s the issue. If they aren’t…make sure they are aligned.
Check the hub isn’t buggered too.

 

[markhodges78]

My bet is its the wrong prop for that lower .. It probably has the correct spline count but the splines probably run the whole length of the hub which is stopping it from going any lower on the shaft. Not all props have splines the entire length of the hub OMC and mercury , mercruiser are interchangeable if you drill some of the splines out of the back end of the hub..

 

[rdrainville]

I got the right prop on it now. I just bought a 17 pitch. The splines went too far down the hub of the old prop. This little rib is scary at 38 mph. It's a very small boat to run that speed. I think 17 might be too much pitch for my goals. It's got all the top end. It wants to cruise in the 25-30 mph hour range and I've gps'd it at 38. It planes at 20 mph ok, but the engine rpms sound real low at that speed. In choppy conditions, it struggles to keep the plane at that speed climbing waves. Since it's a rib, I want to use it in rough water and in the ocean climbing swells. I want to plane at that lower speed easier. Would a lower pitch prop help me with that goal?

 

[Scott Danforth]

What RPM is the motor getting at WOT?

That is what determines how you prop

 

[markhodges78]

I got the right prop on it now. I just bought a 17 pitch. The splines went too far down the hub of the old prop.

Yup that's exactly what I figured... as stated in my post above..

 

[rdrainville]

What RPM is the motor getting at WOT?

That is what determines how you prop

No tach, but it sounds like it revs all the way out.

 

[Scott Danforth]

No tach, but it sounds like it revs all the way out.

So you have calibrated ears? Get a tach

 

[Buster53]

So you have calibrated ears? Get a tach

Agree, without a tach, you are just shooting in the dark.

 

[flashback]

So you have calibrated ears? Get a tach

I have calibration, My ears hear about half of what's there..