propping my 65hp from scratch

[eli_lilly]

Hello,<br /><br />My Merc 650 has an unmarked prop on it. It's pretty beat up so I want to replace it. I have the factory service manual and it recommends one of two props for my 17 foot boat:<br /><br />11.5x13 (32-37 mph)<br />11.75x12 (27-34 mph)<br /><br />The thing I am wondering about is that I do not see this small of a prop listed anywhere, so I am thinking that maybe those dimensions have changed since 1972. I am wondering in what size and pitch the correct prop might now be.<br /><br />Thanks,<br />E

 

[walleyehed]

Re: propping my 65hp from scratch

Props for the '72 650 are available from 8 to 17 pitch from 10-12" diameters, BUT, we need an RPM figure with a known prop to suggest anything..

 

[WillyBWright]

Re: propping my 65hp from scratch

There are two versions of 650s. Yours is probably a 4 cylinder. The 3 cylinder came out later. Yours uses a larger prop than the ones you describe (if it's truly a 72). The same prop fits inline-4 65s thru inline-6 150s. Depending on the boat, it could need anything from a 13 thru a 21. The 3-cylinder versions use the props you describe and came out later in the 70s.

 

[walleyehed]

Re: propping my 65hp from scratch

1972 650 uses the small props, willy...the last year the large props were used on a 650 was 1970 on the 4-cyl and '71 on the 2-cyl. The only 650 listed (By Merc) to use the 10-12" diameter props is 1972-1976.

 

[eli_lilly]

Re: propping my 65hp from scratch

It's a 3 cylinder 72. I'm sure of the year based on the serial number and also the factory manual I have has it in there. That's also where I got the suggested prop from, there was a chart. The issue I have is that the current prop is of unknown pitch and diameter and has no markings on it, so it's useless for any testing.