Best years for OMC 10 horse?

[frankr]

In my not-so-humble opinion, eliminating the powerhead pulling requirement was the worst thing they ever did to that series. Sure it made it easy, but it also eliminated the requirement to at least look at the crankshaft carbon seal. One of the biggest causes of thrown rods, even though most people blame it on the oil.

[johnyrude200]

I’m thinking that if a conversion were to be done it may be difficult in the first place. The older 5.5 exhaust housings are not molded to have an orifice with a slot to accommodate the role pin in the driveshaft. So all they have is the roll pin with the carbon seal, spring, gasket, and brass cup configuration sitting on them. The 6hp motors hold those seals in place, with the role pin compressing the seal against the lower crank/bottom of the powerhead.

I’m not sure if it would be possible to get everything lined up and inserted back into the lower crank (although maybe it wouldn’t be that bad?). If that WERE possible, removal of the gearcase would still allow to inspect that carbon seal, because that whole set up would come down every time you pulled off the gearcase. Again — putting it back together might prove challenging! It would need to be done with the motor almost perfectly vertical because I would think the carbon seal set up would fall off the driveshaft if tilted much. Plus the top of that ‘stack’ still needs to get lined up perfectly with the recess at the bottom of the powerhead.

Even with the 6hp set up, I’ve snapped so many of the roll pins trying to get everything lined up, it’s like trying to hit a bulls eye because it all has to be exactly right to go back together, particularly trying to get the brass shift connector from the lower gearcase shift rod lined up with the upper shift rod perfectly…that is…after getting the roll pin past the slot and THEN the driveshaft splines, then the shift linkage into the brass connector. Even been so frustrated a few times I end up just removing the powerhead to get it done "quicker."

[shoestringmariner]

quote FrankR:

In my not-so-humble opinion, eliminating the powerhead pulling requirement was the worst thing they ever did to that series. Sure it made it easy, but it also eliminated the requirement to at least look at the crankshaft carbon seal. One of the biggest causes of thrown rods, even though most people blame it on the oil.

Frank, any chance you would mind elaborating on this? It sounds like an interesting and important tidbit for newbs to understand, this one included.

[johnyrude200]

There is a carbon seal that the driveshaft roll pin compresses into the bottom of the crank/powerhead. This circulates oil mix that drips down in the crankcase and helps keep the motor lubricated. If this seal is missing, broken, or in most cases, the roll pin on the driveshaft is not replaced or broken when people service an impeller, than the motor runs without proper lubrication leading to accelerated wear and tear.

If you take a look at a parts diagram in the gearcase section you’ll see the parts we’re talking about. Basically a couple of cups, spring, seal, and metal ‘washer’ type thing that sits on the bottom of the crank. Both the 5.5 and 6hp motors share the same design. I mean, basically the 6hp is a 5.5 with needle bearings (slightly tuned carb….?…thought it was just the switch to needle bearings that upped the HP by 0.5)

[frankr]

quote ShoestringMariner:

quote FrankR:

In my not-so-humble opinion, eliminating the powerhead pulling requirement was the worst thing they ever did to that series. Sure it made it easy, but it also eliminated the requirement to at least look at the crankshaft carbon seal. One of the biggest causes of thrown rods, even though most people blame it on the oil.

Frank, any chance you would mind elaborating on this? It sounds like an interesting and important tidbit for newbs to understand, this one included.

Actually, I figure I’ve said it so many times people are sick of hearing me. And I’m sure some don’t believe it anyway. But here goes, one more time. That seal keeps water out of the crankcase. The oiling system actually then pumps it throughout the crankcase. Not a lot of water like what would cause poor running, but enough water to cause bearing wear. And worse yet rust of the crank journals in storage. When you start it up, that rust scours and scrapes at the rod bearings. Remember the "bearing" is a thin coat of silver plating, prior to the needle bearing rods.

I keep preaching that the seal needs to be in 100% condition and always replace the 303347 o-ring and 303355 gasket whenever it is apart.

[shoestringmariner]

Great, thanks for the info gentlemen, very much appreciated

[fleetwin]

quote FrankR:

In my not-so-humble opinion, eliminating the powerhead pulling requirement was the worst thing they ever did to that series. Sure it made it easy, but it also eliminated the requirement to at least look at the crankshaft carbon seal. One of the biggest causes of thrown rods, even though most people blame it on the oil.

You are so right Frank. The later models, with the cup in the exhaust housing actually made matters worse. Trying to pull that gearcase down slightly, removing the coupler screw, and aligning the driveshaft pin with the slot in the housing, is near impossible. I have rarely gotten a gearcase down without shearing the roll pin off. I’m sure many 6hps have gone back together with the sheared roll pin, not to mention cobbled up shift rod coupler screw. I am ashamed to admit, that as a young technician, I know I probably overlooked a few myself.
Removing the powerhead on these engines only takes a few minutes, provided the powerhead screws have been out before and lubed up on reassembly. Here is a rare case where OMC spent more money in an effort to make things easier to work on, but created more long term problems.
This lower seal assembly is not understood by most technicians that deal with it, heck, I still don’t fully understand how those crazy pieces could work correctly.

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