'73 Merc 500 50hp Michigan prop unidentifiable. Wrong prop?

[Intune]

My FIL gave me this boat & I am trying to fix it up. It?s pretty cool. It steers from the front seat with a slot machine-type handle. Somebody told me they call it a crappie boat.


1) Performance issue you are trying to correct.-
Prop is chipped & slightly bent.

2) Current prop manufacturer, model, aluminum or stainless-
Aluminum. The only markings are-Michigan PR 337

3) Current prop diameter and pitch (required).
I have looked everywhere online as to what prop this is & came up skunked.

4) Wide open throttle RPM and speed with an average load (very helpful).- No tach. It gets up on plane well with 400+lbs of people & equipt.

5) Engine/drive make, model, year, and HP-
1973 Mercury 500 50hp

6) Boat make model, year, length and weight-
1973, Skeeter K-4 Metro 15.33 foot outboard. The weight of the boat is 675 lbs. 400lbs added for people.

I took the prop off to find some info on it & it was only attached with a nut and then a larger knurled thing (sorry, best I can describe it) with splines. There is no tab washer or brass washer like I have seen in some of your prop removal diagrams. Also, where the shaft comes out of the lower unit there are four evenly-spaced ports(?) (sorry again) These are packed with hard rubber but not smoothly. It doesn?t look like the rubber belongs in there. Are these exhaust ports & should I dig the rubber out?

Man, I feel pretty stupid right now. I don?t know what pitch or diameter this Michigan prop is & I can?t tell you guys what rpm or speed. Thank you in advance for any help you can give with the terrible info I?ve provided.

 

[steelespike]

Re: '73 Merc 500 50hp Michigan prop unidentifiable. Wrong prop?

Did you check the area under the prop nut for some numbers.
See if you can find an after martket service manual at the library;
for an exploded view of the lower unit.
I don't think the rubber should be there the exhaust should flow freely through the hub.Perhaps the rubber is from a destroyed prop hub.Or perhaps impeller pieces somehow got through the system.If you can't find any numbers a prop shop can measure it for you and repair it.You could get yourself a tinytach about $40 and easy to install.
A gps will give you the speed. If you get the motor running make a couple of runs and get us the prop size and the performance numbers.We can help you get setup right.

 

[hwsiii]

Re: '73 Merc 500 50hp Michigan prop unidentifiable. Wrong prop?

Intune, Spike is right as always. Send us a closeup picture of the prop shaft and the rubber you are talking about and I am sure we can help you.



H

 

[Intune]

Re: '73 Merc 500 50hp Michigan prop unidentifiable. Wrong prop?

Thanks guys. The problem was that I had no prop at all to run with to get any numbers re: RPM & MPH. I should have been more clear. I knew better than to ask, "which prop?" Michigan PR 377 just wasn't to be found anywhere.

I searched the iboats store under "Mercury Outboard Boat Propellers (Standard rotation)" & came up with zilch for a 1973 500 50. It gives props for thru hub, 13 tooth splines for-
'74-'76
'77 and newer
'77-'84.

I called the 1-800# for help. The guy was very helpful. I warned him about my futile search but he was on a roll. "Make? Model? Year?" Taptaptap, clickclickclick... Then...
Silence...

"What year was that again?" I'm bummed but smiling now.

"Is it a Bigfoot?"
Naw, knew we're not gonna get it that easy. (Bigfoot was "all years.")
See what I mean now?

"I am so sorry, sir, this is weird. Give me your phone# & I'll research this & call you back."
Sure, no prob.

That was yesterday morning. He must still be researching... I believe it 'cause I re, re, re and re searched.

But yesterday, in the late afternoon I remembered two words that some of you guys say a bunch. "Prop shop." I thought missing out on a V-8 drink hurt my forehead but it's nothing compared to this bruise.

20 min drive. "I need a prop, please."
"Let me see... 10.5x15?"
I have no idea.
"Let me go check it to be sure."
Comes back in a minute with my old prop & a new one in a bag that looks like it's twin (without the chips, cracks & bends.) "This outta fix you up."

$76

Then I was telling him about the RPM, WOT and MPH method that you guys talk about & he said that was exactly how to do it. Every boat, load, etc is different.

The rubber was on the thrust washer. (See, I'm learning.) I picked it out, greased the spline & mounted the prop today.

Tomorrow. I go BOATING!

Thanks all.

 

[steelespike]

Re: '73 Merc 500 50hp Michigan prop unidentifiable. Wrong prop?

Great isn't it swell when a plan comes together.Let us know how it does.

 

[raysprops]

Re: '73 Merc 500 50hp Michigan prop unidentifiable. Wrong prop?

just found your post (I've been away for a while), your original prop was a 10 1/4 X 12P. the one you got was a PR 343 if it was a Michigan. Wish I'd seen your post sooner, I have Prop cataloges going back into the 70's and even earlier.