Pin Drive Lower Unit Question

flash1977

Cadet
Joined
Mar 13, 2009
Messages
23
I bought a boat and motor from a guy a couple weeks ago. The boat is an 84 model but the motor, an evinrude 25 is prior to 78 according to an OMC shop close to the house because it still has a pin drive lower unit.

What I want to know is if there is a way to convert it or even replace it with a spline shaft for a clutch prop?

I ask this because I am going to give the motor to my dad and he is no longer able to change the pin on the fly if it were to sheer while boating because he has torn his rotor cuff 3 times in the past.

Also, I have been told that the power head is the same on the 25, 30, and 35; however, I have a 1982 Evinrude 35 in the shed with a bad lower unit but have noticed that the powerhead on it is significantly larger than the 25 hp.

I appreciate all help and look forward to making this into a project if it is possible to do.
 

jay_merrill

Vice Admiral
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Dec 5, 2007
Messages
5,653
Re: Pin Drive Lower Unit Question

Please define what you mean by "clutch prop."

That said, the motor is what it is. I doubt that you can convert it to whatever it is that you are referring to.

BTW, I have torn rotator cuffs in both shoulders and don't understand why that should prevent replacing a shear pin. If you mean that he wouldn't be able to reach over the transom of the boat, I wouldn't advise trying to change a shear pin that way, anyway. The best way to replace one "in the field" is to get to shore and pull the stern of the boat to the beach, with the engine tilted up. This alllows you to work in a normal position. Since you don't have to raise your arms while working this way, which is usually the issue that people with rotator cuff injuries have difficulty with, there really shouldn't be a problem.
 

freddyray21

Commander
Joined
Jun 10, 2006
Messages
2,460
Re: Pin Drive Lower Unit Question

the pin in the drive is not actually a "shear pin" it is a drive pin. the propeller will still have a rubber hub in it. It he is not able to change a pin drive he won't be able to change a spline drive either. Both involve taking the prop off.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,189
Re: Pin Drive Lower Unit Question

I haven't actually swapped the shafts, but I am pretty confident that it can be done. As suggested, compare the rest of the parts.

Yes, you are supposed to be using a stainless steel "drive pin". They are tough to break, but it can happen. Anybody insisting on using a soft brass pin is just asking to be changing them frequently. Pin or spline, they all have the rubber hubbed "clutch" prop.

As for the other question asked, there are two basic powerheads. The 18-20-25hp motors were all 22 cubic inch displacement. Then they came out with the 35hp which was bigger, but kept the 22 cu in as a 25hp for awhile. There are also two basic lower units. The pin drive was changed to a spline drive, but the overall basic unit was the same. The 35hp, along with a different powerhead, also introduced the second lower unit, the one with thru-the-prop-hub exhaust. Again, the older unit continued to be used awhile also. Eventually, they all used the larger powerhead and prop exhaust. So.o.o.o, you just cannot make the blanket statement that "they are all alike".
 

lindy46

Captain
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Nov 27, 2008
Messages
3,886
Re: Pin Drive Lower Unit Question

Has anyone ever actually "sheared" a pin? I've been running boats for over 50 years and I can't recall ever actually "shearing" a pin. I've damaged a few props by hitting obstructions but don't remember the pin actually breaking.
 

CATransplant

Admiral
Joined
Feb 26, 2005
Messages
6,319
Re: Pin Drive Lower Unit Question

Has anyone ever actually "sheared" a pin? I've been running boats for over 50 years and I can't recall ever actually "shearing" a pin. I've damaged a few props by hitting obstructions but don't remember the pin actually breaking.

Yup. I sheared the stainless pin on my 1958 35 hp Johnson. The prop hooked up with a rock, the pin sheared, and the prop damage was minimal. It all depends, I guess, on the nature of the situation. I was surprised, but I had a spare drive pin in my toolbox, so I changed it and kept fishing.
 

F_R

Supreme Mariner
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Jul 7, 2006
Messages
28,189
Re: Pin Drive Lower Unit Question

Has anyone ever actually "sheared" a pin? I've been running boats for over 50 years and I can't recall ever actually "shearing" a pin. I've damaged a few props by hitting obstructions but don't remember the pin actually breaking.

More often than actually shearing it, they sometimes wear themselves in two. Especially with a shaft with a worn hole.

I'm reminded of the time I sold a new 2hp motor to a guy and gave him the speil about it being a drive pin and not supposed to break. Well a few weeks later he was back with his tale of woe. Seems he took the motor up north somewhere and put it on his canoe and motored way up to the end of a big long lake. There he shot a moose and loaded it into his canoe and headed back. Tangled with a rock and busted the drive pin. Didn't have a spare, and took forever to paddle home. So he sez to me, he sez "You told me that pin wouldn't break" etc.etc.

So now I always add "but it is possible to break it".
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
26,944
Re: Pin Drive Lower Unit Question

Flash, First of all it is easier (physically) to replace a drive pin, then to change a splined prop. The drive pin on those old Johnnyrudes is removed after taking out a cotter pin and the plastic prop nut.

To remove a spline prop, you need to remove a large nut, which is fairly tight.

BTW I was able to break a drive pin on my old 35HP Big Twin. I hit the remains of a wooden bulkhead at planing speed. That was a fairly thin brass drive pin. My Fat-Fifty had a 5/16 stainless steel pin. I never could break that one, but I was able to chew up some props.
 

flash1977

Cadet
Joined
Mar 13, 2009
Messages
23
Re: Pin Drive Lower Unit Question

Thanks guys for the help. I actually sheered a pin yesterday while running the river and kind of saw how rigorous it can be to change the pin where I am at because there simply isn't a bank to pull the boat up on. We have a lot bluffs/ high banks where pulling the boat up isn't an option. Also, with the Mississippi tug traffic, you have to be quick to avoid a nasty situation.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,189
Re: Pin Drive Lower Unit Question

BTW I was able to break a drive pin on my old 35HP Big Twin. I hit the remains of a wooden bulkhead at planing speed. That was a fairly thin brass drive pin. My Fat-Fifty had a 5/16 stainless steel pin. I never could break that one, but I was able to chew up some props.

See there, that is what some of us keep preaching. Your 35 is supposed to have a stainless steel drive pin, part number 304575, not brass. If you use brass, plan on shearing it.
 

jay_merrill

Vice Admiral
Joined
Dec 5, 2007
Messages
5,653
Re: Pin Drive Lower Unit Question

Has anyone ever actually "sheared" a pin? I've been running boats for over 50 years and I can't recall ever actually "shearing" a pin. I've damaged a few props by hitting obstructions but don't remember the pin actually breaking.

I've sheared plenty of them. I had a '58 Erude 5.5hp motor as a kid and probably sheared 3 or 4 pins each summer. I also have a '73 4hp Johnson now and have sheared a stainless pin in that.

I do learn something every time I come in here, though. I consider myself to be pretty well informed when it comes to older OMC outboards, but was never aware of the distinction between a shear pin and a drive pin. The same is true of the use of the term "clutch" when referring to the rubber hub in a "pin drive" prop. We just called them "shear pins" and "hubbed props."
 
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