1970 Merc 500 - Need help identifying what prop I have please!?

[Roadblock]

Bent the prop on my 1970 Merc 500. I believe the motor to be the original that came on my 1970 Mirrocraft Ski-N-Troll so I assume the prop is matched to the boat setup?

The prop is very worn too and I can barely make out the lettering but I believe it says:

10 1/4 x 1

Can someone tell me if this is complete an what it means? Looking to just get a basic replacement.

Thanks!

 

[Fun Times]

Hi there roadblock, Unfortunately it looks like your missing an important number to know exactly what pitch you have there. Also you'll want to count the splines on the shaft to help narrow the search. Have a look at this link to see if it will help you out some. http://forums.iboats.com/forum/gene...-topics/559024-1967-mercury-500-prop-question .......

http://www.mercruiserparts.com/Show...962/NOIMAGE&inbr=474&bnbr=24&bdesc=PROPELLERS

<That info can be found inside here,
http://www.mercruiserparts.com/selectSerailRange.asp?doc_nbr=500,+50

 

[steelespike]

Look carefully near the base of the blades or in the area under the prop nut.
If I had to guess I would say 101/4 x 11" Consider that a starting point.

 

[Roadblock]

Well I definitely see 10 1/4 x 1 stamped into the base of one of the blades. That is where I got that number from to begin with. However going back and looking again I can clearly see the number starts out on the 10 side nice and deep but as it works it's way across to the x 1, the 1 is almost not readable. It clearly wasn't stamped in there deep enough. My guess is that last number was missing from the factory in 1970.

It has a 13 spline.

OK so I need some clarification on years. When I look up Merc props, even brand other than Mercury the lists are broken down like this:

Merc 50HP 500 13 Spline 1970~73
Merc 50HP 500 13 Spline 1974~77
Merc 50HP 500 13 Spline 1978~84

I only found ONE dealer that listed anything for a 1970~73, it was a 10 1/4 x 13 and it was no longer available. No one else has anything listed for 1970~73, only 1974 to 1984.

That said when I went to my local Marine shop the other day they tried to sell me a Mercury Black Diamond 10 3/8 x 13, 13 Spline for $156.99 and said it would work just fine on my motor and that the prop specifically for that motor was no longer available.

So lets say I just CAN'T find a prop... I didn't actually break my prop. I bent it all to hell on a river trip. The whole back end of my boat was shaking so bad I thought my transom was going to rip off. In order to get us back to the trailer, I removed the prop and banged out some of the bad bends with hammer and got it to an acceptable point river side, which got us home OK. The vibration was barely noticeable WOT but it vented bad. I kept having to drop the throttle to avoid over rev'ing then slowly increase back into it to get the vibration down. Was a fun 45 minute trip let me tell you!

I have a small chunk missing on the edge that I'm 100% sure would be welded back in. They wouldn't even need a piece of aluminum, just toss some weld in there and grind it down. You can definitely see hammer marks but nothing super bad, the aluminum was pretty tough.

So that said I believe this prop COULD be fixed but without knowing the pitch, can they fix it? One of the 3 blade is almost completely undamaged. Could they measure the pitch via that blade?

 

[Roadblock]

Please read my above post BUT...

*Update*

So I did some more digging about different brands and I see the ONLY prop anyone ever lists for a 1970~73 Merc 50HP 500 is a 10 1/4 x R 13. Solas, Michigan Wheel etc, they are all 10 1/4 R 13, 13 spline for 14~16 foot ski boats, all loads. Michigan Wheel is 2 blocks from my house so I called and they verify the only prop they sell for my boat is a 10 1/4 R 13 and it's good for any load weight on a boat 14 to 16 feet. Which I have a 16 foot Mirrocraft Ski-N-Troll soooo um yeah.

So I guess the 1 must be missing a 3 at the end then?

 

[steelespike]

So no numbers under the prop nut? Is a 13" the only prop available period. Or the only prop for your specific size/style boat.
Assuming the old one was a 13 how was the performance? Strong hole shot?Respond well to a load?

 

[Fun Times]

That said when I went to my local Marine shop the other day they tried to sell me a Mercury Black Diamond 10 3/8 x 13, 13 Spline for $156.99 and said it would work just fine on my motor and that the prop specifically for that motor was no longer available.

So that said I believe this prop COULD be fixed but without knowing the pitch, can they fix it? One of the 3 blade is almost completely undamaged. Could they measure the pitch via that blade?

He's correct in saying that the black diamond propeller line will work on your engine.


Sure sounds like your original prop is repairable. Do you have a propeller repair shop in your area that could take a look at it for you? If you're unsure, just go a Google search about prop repair in your area. A good repair shop will be able to size the prop up for you. Also I updated the links in post # 2 so they now work. Good luck. Edit: I just saw post # 5.

 

[jestor68]

If you would visit the Propco Propellors web site, you will see that they produce a full line(10-17 pitch) of aluminum props for your older Mercury motor.

They specialize in producing props for older motors where the props have long since been out of production, and/or the manufacturer (Chrylser,OMC) is no longer in business.

Just google "Propco Props".

 

[Roadblock]

OK! So we have identified the prop. I was able to get some info out of Michigan Wheel and West Michigan Prop and the factory prop included on a 1970~73 Merc 500 50HP was in fact a 10 1/4 R 13, 13 spline. Michigan Wheel made a replacement for years but it was discontinued. They sent me over to West Michigan Prop who just happened to have a rebuild factory original 1970 Merc 500 prop in-stock, it's the 10 1/4 R 13 that I already have. Was rebuilt and looked brand new. They gave it to me for $66.00 dollars!

Then he quoted me $23 or so to rebuild my bent prop. He said if they have to weld it will cost a little more but it all depends on what they have to weld. I know the edge of one of the blades will need roughly a bead of weld and then need to be ground but they said thats nothing, some people are missing pieces of prop blade or whole blades so it should be close to the estimate.

So I've got a almost new looking prop and I'll have a spare in a week! For what I do, really, a stock props are good enough. Someday I would like to find a prop that will gain me just a little speed. I just put a GPS speedo in my boat and I can go 25~26 on a bent prop so I hope a gain a little. I would like to get 35~45 out of the boat and I see Merc HAS props rated for that on the Merc 500 depending on load so I would hope I could get there someday.

 

[Roadblock]

Updated... Just got back from picking up the prop from West Michigan Propellers Inc., $66.00 out the door got me a totally reconditions factory original 70~73 Merc 10 1/4 x R13, 13 spline prop. Looks GREAT!

That said apparently the prop I had was NOT original Merc. It was made by Michigan Wheel Prop. Inc. West Michigan Prop Inc is reconditioning that one for $16.00 dollars since I bought a prop and they said it would come back looking brand new. Michigan Wheel no longer sells them but when they did, they ran $159'ish so good deal I guess!

The Michigan Wheel prop is a little beefier but spec wise is the same but I will probably go back to running the Michigan Wheel prop and keep this Merc OEM for a spare. Just mounted it, fits GREAT!

 

[steelespike]

Sounds like good deal.It will be interesting to see how your results measure up to original.
Might be interesting to see if there is any difference between the two.

 

[Roadblock]

Tell you what, the boat runs SMOOTH as hell. I've been having planing issues so I installed a SE Sport 300 Hydrofoil but I didn't really feel it helped too much. I mean it DID make the boat plane but it still took longer than I thought it should.

With the reconditioned original OEM Merc prop it planes super quick and the whole boat is way smoother with this prop than it ever was with the Michigan Wheel prop I had.

My guess is that the prop was out of whack before I bent because it was never this smooth.

I will be interested to see how the Michigan Wheel Prop runs once it comes back from being rebuilt. If it's as smooth as this one is running, I will probably go back to the Michigan Wheel Prop as it was a little beefier and keep the OEM on board the boat as an emergency spare! I mean I already bent one prop on the river and I never thought it was going to happen so a spare will be a nice thing to have!