66 Merc 50 changing gear ratio

[Alumarine]

Ok here we go again.

I've got a 66 Merc 50 long shaft with a gear ratio of approximately 1.6 running a 9P prop which sucks big time.

I have a LU from a 50 merc short shaft with a 2.0 gear ratio from a newer motor. The newer LU won't fit on my older motor the front 2 bolts are spaced a bit differently (never mind that it's a short shaft).

How difficult is it to swap the LU gears from the new to the older?
Will they even be compitable?

I have a manual on order.

Thanks for any help.

 

[diaric]

Re: 66 Merc 50 changing gear ratio

i doubt it would fit, different bearings seals etc, most of the parts are different sizes. u would probably need to ask an old time rebuilder for sure. kinda would be nice cause then prop shaft might change and you'd get away from them hard to find 11 spline props. if you ever need to get rid of that old motor for parts, let me know, i may need them lol.

 

[Alumarine]

Re: 66 Merc 50 changing gear ratio

Thanks for the info. Sorry not, about to get rid of this old motor, but it would be nice to be able to use a wider selection of props.

I guess I'll wait til I find a long shaft donor motor of the same vintage.

i doubt it would fit, different bearings seals etc, most of the parts are different sizes. u would probably need to ask an old time rebuilder for sure. kinda would be nice cause then prop shaft might change and you'd get away from them hard to find 11 spline props. if you ever need to get rid of that old motor for parts, let me know, i may need them lol.

 

[diaric]

Re: 66 Merc 50 changing gear ratio

you sure about that gear ratio? the only info i can find is 1.7 : 1 and it doesn't differentiate between between long and short shaft. but again, i can't find confermation.

 

[Alumarine]

Re: 66 Merc 50 changing gear ratio

No, I'm not sure about the ratio.

It looked like approximately 1.6 turns of the prop with 1 turn of the crank.

Could very well be 1.7.

 

[diaric]

Re: 66 Merc 50 changing gear ratio

11 pitch was about the most common prop for that motor. mine is running an 11 on an OLD (1960) heavy 1960 fiberglass runabout and will do about 30 mph at 5300 rpm and 2 heavy adults. u should be able to do better if you got it on your alluminium boat.

 

[Alumarine]

Re: 66 Merc 50 changing gear ratio

You would think it could do better but it is a very heavy boat.

I tried a 12p on it and it would only plane if 1 of the 2 people onboard went to the bow.

Whoever turned it into a mini bass boat used 5 STEEL angle irons running the length of the interior to give it strength.

11 pitch was about the most common prop for that motor. mine is running an 11 on an OLD (1960) heavy 1960 fiberglass runabout and will do about 30 mph at 5300 rpm and 2 heavy adults. u should be able to do better if you got it on your alluminium boat.

 

[diaric]

Re: 66 Merc 50 changing gear ratio

i would think it would do a lot better as my boat is not lite. I usually run it with 2 batteries and a minkota on it, it will still do about 24 mph with 3 adults. before I put a tilt trim on it, it was really sensitive to which hole I had the motor set at for planing. have you checked compression etc to see it might be getting a little tired? I'm only a couple years older than that motor and i'm always tired.. LOL

 

[diaric]

Re: 66 Merc 50 changing gear ratio

marc, check out this old chart for prop sizes/ speed / load for your old motor. that 9 pitch is for hauling 2000 lbs. have you tried any other sizes?
http://www.maxrules.com/oldmercs/Propellers/Props/9.pdf

 

[Alumarine]

Re: 66 Merc 50 changing gear ratio

Thanks for the link. Yes I tried a 12p and it will barely plane and won't rev.
Compression is good and it rev's well with the 9p.

You wouldn't believe how heavy this little boat is. 4 guys have a hard time hauling it onto shore.

marc, check out this old chart for prop sizes/ speed / load for your old motor. that 9 pitch is for hauling 2000 lbs. have you tried any other sizes?
http://www.maxrules.com/oldmercs/Propellers/Props/9.pdf