18/20/25 3-lug gearcase compatibilities

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johnyrude200
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18/20/25 3-lug gearcase compatibilities

Postby johnyrude200 » Fri Mar 17, 2017 3:55 pm

Alright, I have a question for an issue I've run into a handful of times. I have had about a half dozen situations where when I pull apart one of these gearcases, between '60-76 for service, I see that the forward gear and or clutch dog is no longer serviceable.

Trying to transplant good parts into it, I have found the forward gear bushing will NOT fit into the gearcase. Now this is not a situation where that little stud is not lined up. It is a situation where that brass bearing that sits over the forward gear is larger in diameter than the recess in the gearcase housing.

I ask this, because I recently pulled a '69 25hp gearcase, to find it had been updated to the rare 3-lug version, which was in mint condition. Trying to put a 2-lug equivalent in I ran into this same problem - the forward bearing will not sit in correctly. I even put a micrometer on both the old brass bearing and the newer roller bearing and found them to be consistent in diameter. In fact, the older brass one came in slightly SMALLER.

I have transplanted one of the complete 3-lug gearset into a '67 20hp with no problem. Was hoping to put aside this gearset for a rainy day and personal use.

What info am I missing here in terms of variants of manufacturing years where things were just slightly different? I mean, the 3-lug version has a needle bearing, thrust washer, and roller bearing in lieu of the old brass bearing.

Looking at M.E., they list the 3-lug gearset as an update for all model years, even with the old 18hp motors.
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johnyrude200
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Re: 18/20/25 3-lug gearcase compatibilities

Postby johnyrude200 » Fri Mar 17, 2017 5:36 pm

Well, solved the problem but have a new question. The forward gear I was using as a replacement has the teeth going in the opposite direction...? The lugs on this one are in very good shape, hence why I may have kept trying to use this over the past year without luck without noticing the difference!

It is exactly the same as the original less the teeth direction.

Was there ever a counter rotation gearbox for this family of motors?
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BillW
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Re: 18/20/25 3-lug gearcase compatibilities

Postby BillW » Sat Mar 18, 2017 5:54 am

I don't know the exact years but the backwards gears show up early, like the '56-'58 range in my experience and are gone by around 1959. This is all subject to very bad memory. But I CAN say that the backwards gears were in a standard rotation case. WHY, I don't know. Maybe it was a mistake that they figured out....

fleetwin
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Re: 18/20/25 3-lug gearcase compatibilities

Postby fleetwin » Sat Mar 18, 2017 12:27 pm

Backwards gear lugs? Would love to see pictures of that.. Wonder is this is why there was always a gear whine in the older 15-18s....

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Re: 18/20/25 3-lug gearcase compatibilities

Postby johnyrude200 » Mon Mar 20, 2017 7:30 pm

here's a pic of the backward teeth forward gear that has given me some hassle over the past year. It is covered in yellow tape now so that I don't make this mistake again!

Can you see which one is DIFFERENT??? :D

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Fisherman6
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Re: 18/20/25 3-lug gearcase compatibilities

Postby Fisherman6 » Mon Mar 20, 2017 8:20 pm

The helix on the gear on lower left is in the opposite direction. Something looks different about the drive lug profile on the upper right, however.
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johnyrude200
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Re: 18/20/25 3-lug gearcase compatibilities

Postby johnyrude200 » Mon Mar 20, 2017 9:07 pm

They're all the same, that was an exposure thing with the cell phone. Of course, bottom left is the backward teeth gear that I have been talking about. Identical to the forward gear for the other motors (micrometer matched very closely).
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fleetwin
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Re: 18/20/25 3-lug gearcase compatibilities

Postby fleetwin » Tue Mar 21, 2017 7:17 am

OK, well that is surely interesting...Just so I know, there is only one gear in your pics with "backwards" lugs, the one on lower left, correct?

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Re: 18/20/25 3-lug gearcase compatibilities

Postby johnyrude200 » Tue Mar 21, 2017 7:46 am

Yes, id have to take a few minutes to look through my parts bins for the pinion and reverse gear to complete the set.

Weird. Anyone have an explanation?
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