TOPIC: Tough time finding this prop for my Merc 500....

Several months ago I found a 1970 lower unit for my 1968 Merc 500. My current motor is a 1965 Merc 500 and it's lower unit has a 11 spline prop shaft. Well, the 1970 lower unit (no intake screen) has a 13 spline shaft. I have contacted dozens of boat shops around the country and have searched EBAY and craigslist. Anybody have a used 13 spline / 11 pitch prop with the part# 48-56244A1 that you no longer use? I would be willing to buy it. It took me three years to track down a useable gearcase, as the 68 can only accept units from 1968-1970.

I'm swapping motors as the 1968 is a true longshaft. (65 has an extension + a few other issues)

Thanks.

Can't believe you are having that much trouble, 13 spline props for your engine are quite common, it is the 11 spline that is getting hard to find. I will look through my pile and see what I can find for you.

Yea, 13 spline props are common. But for a brief period after the switch from 11 spline to 13 spline prop shafts, they left the size of the gearcase and mounting hardware the same as the 11 spline ones. Later models went to a larger gearcase that allowed larger props with thrust hubs on both sides of the prop. 11 pitch props went from 10 3/4" to 12" in diameter. Mine can't handle these larger and more common 13 spline props. (11" max diameter)

Isn't that interesting... OK I will look today for you. I do have a couple of 500's from that era that I was going to restore or part out that have good props on them so cross your fingers! At any rate, it might be possible to swap the lower unit for an earlier or later one or to change out the propshaft in yours for a 11 spline to accommodate the easier to find props. I know I do have a small diameter 13 spline for that gearcase, but it is a two blade and steeper in pitch. I do have a 11 spline three blade 11 incher however, and i still have to check the engines in the garage! There are some things we can do here I am sure. Where are you located?

Cheyenne, WY. Swapping lower units for newer or older ones won't work. That was the first issue I discovered. Shift shaft issues (reverse lock cam) with older models and a slight change with the front studs on later models. One of the Merc experts on this forum brought the slight change with stud position to my attention. The 68-70 Merc 500's were sort of an oddity with regard to lower unit compatability.

Thanks for your help in trying to find a prop. I'm still probing prop shops. Yesterday, Brainerd Props in Minnesota told me to contact a place called Tim's Outboard, as he has a bunch of props for older models.

Thanks for your help.

I may have a prop for you. Let me dig around and I will get back to you this weekend.

Yes, there are differences in the cases, but it may be possible to swap out the bearing carrier and propshaft to make it work, I have done it many times before. I just have to find the right combo, I have several different lower unit cases here so I will take a look and see what swaps with what.

Thanks, but don't bother doing that. I need a prop, but I'm not that desperate. I'll just leave the 65 Merc on the boat until one shows up.

try tim calmes in perry ny,he has a warehouse full of vinage merc stuff, 585-237-0354 0r cell 585-301-5426.
shop number is 585-493-5073,john

I finally got one! Tim's outboard in Hackensack, MN had the prop. It's a brand new Mercury Quicksilver prop from 1970(NOS). $65

Thanks to those that helped including john. Tim calmes didn't have the prop, but I found another place for obtaining parts for my older Mercs.

Hi,
At the risk of falsely creating a problem, I can see some possible problems.
Do you know if the 1970 lower unit ratio is the same as the 1965? I think that a 1965 is a 1.64 to 1, and the 1970 may be 2 to 1 (you could rotate the driveshaft or flywheel, depending on if the lower unit is installed or not, to note how many turns are necessary in forward gear to achieve one turn of the propeller). If 2 to 1, you will need a higher pitch. Note that the elevation could be a factor to consider.
I can be forgetful, but I do not remember the newer props being a fitment issue (assuming the correct propeller hardware is chosen also)(we have dealt with Mercury products for 50+ years, and we were a Glastron dealership, 1964-70). The current 3-blade in an 11" pitch is 10 & 7/8 inch in diameter. The propellers did change as improved designs were found, and can often offer better boat performance (there are certainly exceptions).
Good price for a new propeller which fits, but you may can improve performance with a different one.

Regards,
Joe

www.fergusonpoolemarine.com
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Thanks for the additional info. It has the same gear ratio as the 65. (1.64:1) I boat at an elevation of 7500 feet, so I'm getting less than 40HP out of my Merc 500. I hit 30 mph and 5500 rpm with the 11 pitch.

Hi,
It is pleasing to hear that the gear ratio and elevation were factored into the choice. It would be interesting in a perfect world to see what a current 10 & 7/8 by 11 pitch would do with it's newer blade design, higher rake, and cupping, but with the lower pitch involved, boat planning, handling, and mid-range performance may have been the only noticeable improvement (especially assuming that you do not have power trim & tilt). I would think that the 2 to 1 ratio would be a noticeable benefit to you at the elevation you boat at. Of course, power trim & tilt is a wonderful addition also.

Regards,
Joe

www.fergusonpoolemarine.com
This email address is being protected from spambots. You need JavaScript enabled to view it.

I have a 1971 Merc 500 on my 14 ft Penn Ryan runabout and want a replacement prop. I have a 10 3/4 dia x 13 pitch Mercury prop, part no. 48-56236A1 13P, that I want to replace because I used a considerable amount of force, penetrating fluid and heat to get it unstuck from the shaft. The rubber hub looks OK but I'm not trusting it now. I find 10 3/8 x 13 props, 10 1/2 x 13 and similar sizes in several brands. What props are others using for this outboard? My boat is estimated to be about 900 lbs without passengers.

Well, I want to update this post. I got the new prop and tried it out on my 68 Merc 500. I was down in speed, but RPM's were 5700+. I was getting a very fast holeshot and more ventilation when cornering compared to my 65 Merc. Something didn't seem right. According to everything I have read, the 1970 lower unit could only have a gear ratio of 1.64:1. The same as my 65. It turns out that it is 2:1. Why I didn't check that out with a manual spin of the flywheel, don't ask. I know Joe mentioned up above it could be 2:1, but the lame manual I have showed all Merc 500 lower units from 1965-1979 as 1.64:1. (Also, I had already bought it)

I called Tim's outboard in Minnesota and he had a used 13P prop. I'm going to give that a try. He said a 13P prop on a 2:1 gearcase should be equivalent to the 11P prop with the 1.64:1.

MousamPennYan, the used 13P prop that I just bought has the same part number that you listed. There is a two blade 13P on EBAY that would work on your Merc.