replacing prop issues

[Smedley]

I am replacing the prop on my '82 Mercury 40 hp. The prop that is on it now (existing prop)is not OEM. I have the OEM prop and one like it with different pitch (teh good one). The OEM prop is chewed up pretty bad and I don't want to use it. The existing prop is in similar condition. The other prop is fine. My Problem: When I took off the existing prop, I noticed that it is quite a bit smaller diameter than the good prop and the OEM. I put the good one on to be sure that it would fit and it does. I'm guessing that the existing prop is about a 9.5-10" diameter the good one and OEM are 10 1/2 or there about and have bigger blades. The existing prop has a locking tab on it where the good one does not. I have the repair manual and it looks like when the existing prop was put on, the aft thrust hub was omitted. Now I think I need it for the good prop. The existing prop's sleeve is longer and the outer washer wasn't needed. Can I use some other type of spacer? Does it matter if there is some play in the prop in and out not side to side? How will I get the good prop locked in?<br /><br />This is the existing prop<br />

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<br /><br />the good prop (no retainer for lock tab)<br />

<br /><br />the three together (good, OEM, existing)<br />

 

[walleyehed]

Re: replacing prop issues

The other 2 props are not for that application...<br />The props must have the 2 pins in the hub for the lockplate.<br />I don't think there is an aft splined washer for that application...I had the same engine on the same boat...it now has a 70 on it, but the 40 and 70 (1983) both use the same prop.<br />28-70HP is the application in 13 spline.<br />If you have a dealer near, check on the aft washer...<br />p.s. Good chance with the diameter of those 2 props, they are much lower in pitch..that design is for heavy loads so don't expect any speed if you get them to fit.

 

[Smedley]

Re: replacing prop issues

walleyhed, thanks for the quick reply. the numbers on the existing prop are 48-73136-13P the good prop is a 48-61816A1-12P....does either one of these sound right for this application? I believe that you are right abiout the pins on the hub. The Seloc manual shows an aft washer but I think that is a generalization for how to remove any prop.

 

[Richard Petersen]

Re: replacing prop issues

What animals live in your waters? They always eat off ONLY 1 ear of a prop. I would need a 100 props to match yours.

 

[walleyehed]

Re: replacing prop issues

13P should be close..<br />The 73136 series is for 1977-up..<br />The 61816 is for 1972-1976, 40, 50, 60 and 65HP engines...<br />Your original (73136-13P) is a 10-3/8X13. The Michigan P/N is 031017<br />A 10-3/4X12P is what I used on my 40 on the tracker at 3600ft elevation, and an 11 Pitch would have been better suited in my case.<br />at 500-700ft, the 13P should be fine.

 

[Smedley]

Re: replacing prop issues

Thanks again Walleyehed. I think I found a S/S pretty cheap. Just waiting for the guy to get back to me. He said he thought it was a 17 pitch. What are your thoughts? Is there a cross reference from OEM aluminum to S/S so I can make sure I'm getting the right one?<br /><br />cyclops....the bites out of both of those props are courtesy of my dad, who used to own this boat. One of them got chewed up on a cable when, for some unknown reason, he tried to back up into a boat slip. The other one was probably the result of an equal amount of stupidity! That's why I rescued the boat from him...he's expensive!

 

[Smedley]

Re: replacing prop issues

P.S. Walleyehed...that boat with a 70 hp on it would just scream across the water. Did you have to upgrade the transom any to hang the bigger motor?<br /><br />Any thoughts on a tilt/trim unit for it. It's got power t/t now.....all the power I got in my arms.

 

[walleyehed]

Re: replacing prop issues

CMC makes a TNT that works real well on this size application.<br />A 17P SS ....hummm...that sounds very steep.<br />I would highly recommend a tachometer if you don't have one. I shot for 6200 with both the 40 and the 70 by myself, and this was perfect for 2 people running about 5900 and about 5800 with 3 on board.<br />I did reinforce the transom, but I would have to take a pic to show you how it was done...pretty simple actually...it was designed to eliminate twist as the 70 only weighs about 20lbs more than the 40.

 

[Smedley]

Re: replacing prop issues

Dont' have a Tach but would be willing to got one installed. Is that soemthing I can do myself or would it be better to take it to a shop? <br /><br />with a 17p I would lose RPM but possibly gain speed right?<br /><br />You mentioned elevation in one of your responses. what effect does this have on prop performance. Sorry, I don't know much about the physics of boats. This is the first boat I've ever owned and am learning by trial and error.

 

[walleyehed]

Re: replacing prop issues

Altitude and high temps affect engine performance greatly.<br />For every 1000ft in elevation, about a 3% decrease in power applies. so at 3600ft, I have lost 12-15% of rated power, so you end-up dropping pitch to compensate for elevation, to get max RPM back from sea-level.