pinion gear blowout on newer 25/35’s

[johnyrude200]

Has anyone noticed a tendency where these gearcases blow out the pinion gear (and consequently, the forward and possibly reverse gear splines) after a collision?

I acquired about a dozen of the post ’95 motors right into the 2000’s, and several had blown gearcases. While pulling these apart, just about every one of the pinions were stripped right down to the core. Clutch dogs still look mint, but forward gear, bearing, pinion gear bearing, thrust washers…all different degrees of being toast. A few needle bearings floating around in the wrong places too if you know what I mean.

Some of the housings didn’t even show any signs of a collision. Some were pretty obvious. Couple of twisted driveshaft splines at the gearcase end.

I notice that less the pinion and driveshaft, the rest of the gearcase appears the same as prior iterations; the driveshaft is longer with a thinner taper at the gearcase end for more grab into the pinion, and the orifice of the pinion gear itself is narrower and accepts about 1-1.5" more of the driveshaft.

Did the older style (larger diameter driveshaft, but less length and consequently less section into the pinion) have a tendency to strip out the driveshaft splines or break at the neck?

[frankr]

I’ve heard of the problem, but never personally seen one. I was under the impression that the gear teeth strip, then the chunks lock everything up. Wouldn’t that be why the splines strip or shaft breaks? I don’t know, just asking.

[fleetwin]

Pinion failure/driveshaft breaking/twisted splines are not uncommon for many styles of gearcases after hitting an obstruction, not just the 25/35 OMCs. SS props usually amplify the internal damage as well. Generally speaking, the 25/35hp thru hub gearcases are pretty rugged/reliable. Like anything else, people will find a way to break this stuff, especially during panic shifting maneuvers at high RPMs. I remember that OMC did elongate that pinion neck, utilizing two needle bearings, I’m guessing this was to give the pinion more support to ensure it stays properly positioned. It doesn’t seem like this deign change would make the pinion weaker/more prone to failure though.

[johnyrude200]

Well after a couple of hours of playing with one of these ’04 gearcases, I found out the hard way that you CAN NOT switch the pinion gears from a short-neck/older version of the gearcase with the newer long neck version.

The splines on the pinion have a larger diameter on the older version. So if you do this, YES, the pinion will engage forward gear. But as soon as you drive the prop shaft through the forward gear and into the forward bearing, this locks things up to the point where things will almost not even turn.

And on top of that, the shift detent spring and 2 little ball bearings won’t go in the right way. Let’s say there is about a half dozen of those little balls scatter across my garage and I won’t find them again for a month or two…only accidentally. Feeling pretty deflated about wasting all that time!

If only I could find a few driveshafts for these newer units for short cash. Have a few gearboxes in mint condition with no driveshafts.

[fleetwin]

After talking with Joel at Thompson, I found I was misunderstanding what he is describing. I was thinking the pinion gears he spoke of were splitting apart/breaking up, which is usually due to hitting something or perhaps shifting at high RPMs.
But, it seems like the failures Joel is seeing are more like the pinion teeth being wiped off leaving the rest of the pinion intact. If this is the case I am thinking these failures are due to a lack of lube/improper refilling procedures. Joel said these engines came from a boatyard that was mismanaged, and they probably had inexperienced help changing/refilling gearcases.

[jerry-ahrens]

And of course, we all know that every outboard owner always changes his gear lube every Fall……. LOL! I t really amazes me how people neglect the gearcase oil on an outboard, or a stern drive for that matter. I always ask when I’m working on an engine or drive, if the owner has changed the oil in the last year. The replies vary….” Well it doesn’t have many hours on it” [my favorite] or ”I don’t know” or ” Is their oil in their somewhere?” I remember my years at the dealership when I used to see Bravo Three lower gearcase driven gears with pits or cavitys in them. The gear lube would come out black with that nasty smell. Mercury used to tell us that it was caused from dirty gear lube or lack of changing it.

[johnyrude200]

"If it smells like rotten eggs, it’s old."

If it sparkles in the light…you have bigger problems 😮 😯 😕

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