Mix lower unit gears and gearcase halves?

[olcah]

I am working on a 1956 Johnson RDE18 30 hp. Lower unit gears and bearings are not savable due to bad rust. I also have a 1954 Evinrude 25 HP parts motor. The gears and bearings are same part numbers as the RDE18 so will interchange. However the forward gear is not useable because the corners of the gear surfaces that mate with the clutch dogs are worn away.

Johnson says that the pinion gear, forward gear and aft gear should be replaced together. If I "mix and match" the gears depending on what I can find will that work ok?

Another question, the lower half of the case with the skeg was badly cracked and poorly welded. Top case is OK. I have a lower half case from another Big Twin that bolts up to the top case. Will that work ok?

Thank you.

[david-bartlett]

Charlie,

I have done that sort of thing often with the 18hp OMC motors without issue. The books and repair people will say not to mix case halves, but it is your money. On a motor that will see moderate use it is worth a try until you can find another lower unit.

[auldscott]

The parts were fully interchangeable when new, but each gearset and bearing wears to a unique pattern. If it were my motor and I didn’t want to buy new parts ($$) I would put in good used parts and check them for friction and noise. If not too bad, I’d run the motor.

[vintin]

I could be wrong on this but it seems I’ve read that the foot was cast as one piece and then cut into two pieces. Or maybe it is that the two halves are cast separately, machined on their mating faces, assembled, then machined to accept the bearing races and seals as a whole.

If so then it’s not about the part numbers.

Just tossing this info out there.

I’d still go for it.

[frankr]

Vin Tin got it. The two halves were bolted together, then bored for the internal parts. In theory, there are no two alike. But we all know that the theory doesn’t always hold up.

[chris-p]

I know they say not to do so, but ive swapped a few skegs in my day with no worse for wear. Assemble it dry and go through gears/shift gears and try it out. IF ok, seal her up.

Who knows how many gear sets Ive swapped around! I definitely would not worry about this, unless one of them is grossly worn.

[dave-bernard]

don’t forget they had to warranty the parts so they made sure all ? were covered. when new.

[1946zephyr]

Okay, heres the deal. I have been told the same. However. Bolt the two halves together and check with an inside micrometer (where the bearings seat) and make sure there is no "out of roundness" If not, then you’re in luck. I have heard of folks mixing and matching with positive results, but check the bearing race seats and make sure there is no out of roundness.

[olcah]

Thank you everyone for all the great info/advice.

[Mumbles]

The five bolt gearcases had two different style of gears in them, square cut and not so square cut. I don’t think you could interchange these ones without realizing something’s wrong.

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