Lower Housing Cracked 1957 Big Twin

[mr-asa]

quote kees:

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upload an image or photo from your computer or the web
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or create something with “photobucket”
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[danblue]

So, lets assume the gears and everything are in good shape which I believe they are. How easy would it be for me to simply buy a new seal, and simply replace the cracked shark fin housing with the one I have on my 30hp Johnson Seahorse?

Simply clean out the gear area, put the seal on correctly, put the new housing on, use the sealer liquid on the screws to attach the new shark fin housing as the book advises, fill the unit with oil as prescribed, and just go with that?

[phil-b]

I’ve heard that the gearcase was machined as a pair, so you can’t replace just the "skeg" or "fin".

On the other hand I’ve also heard of people trying it, and haven’t heard of catastrophic results!

Installation of a new gearcase/lower unit is easy to do yourself, and worth learning so you can replace the water pump impeller.

[mr-asa]

quote Phil B:

I’ve heard that the gearcase was machined as a pair, so you can’t replace just the “skeg” or “fin”.

if that were true, I’d expect you’d have to lap the two surfaces whenever you separated them? Anything like that in the manuals?

[chris-p]

The skeg and gearcase are a matched set, it is not recommended to change just the skeg. However, I may have seen it done successfully before 😉

[jerry-ahrens]

I would think you could buy another complete lowerunit at one of your local meets. There should be a lot of those around. And yes the 56 unit you mentioned will interchange. One thing to check on the 56 gearcase is the condition of the brass bushing located underneath the water pump wearplate. You will need to remove the driveshaft seal to get it out. If this bushing is worn the driveshaft probably has some wear too, where the two meet. This causes the shaft not to stay centered during operation, and allows water to come in. I always replace the shift rod o ring as well,[whether it’s bad or not] anytime I service one of those for the first time. These two items are what usually leaks on these gearcases, in my experience.

[fleetwin]

OK, well not sure if the gearcase was full of water causing the freeze crack, or if you hit something while underway, or perhaps something hit your engine while the boat was parked on the trailer. The skeg/fin and upper gearcase housing are a matched set, so please do NOT attempt to use a skeg/fin from another gearcase housing.
At this point, you could remove the skeg fin, or just loosen the other screws allowing the skeg to drop a little to inspect the gears.
You could post an ad to find another complete gearcase or just a gearcase housing.

[gjonz]

Either way…the skeg and lower unit are a matched set. So I’d replace the whole thing. These two items are bored out at the same time, so using a different skeg could result in binding or distortion of the seals or premature wear of parts etc.

Your mileage may vary… 🙄

Good luck. At least it’s a common gear case.

Greg

[danblue]

Just so I’m clear, the shark fin housing part and the above housing that attaches to the shark fin part are to be thought of as one unit correct?

So if I buy a replacement, I need to make sure the gears and guts that are down in the shark fin part are in good working order.

Furthermore, since the shark fin housing has cracked, the whole unit is worthless as it is….I can’t just slap a new shark fin housing on this thing.

Thanks!

[danblue]

quote fleetwin:

OK, well not sure if the gearcase was full of water causing the freeze crack, or if you hit something while underway, or perhaps something hit your engine while the boat was parked on the trailer. The skeg/fin and upper gearcase housing are a matched set, so please do NOT attempt to use a skeg/fin from another gearcase housing.
At this point, you could remove the skeg fin, or just loosen the other screws allowing the skeg to drop a little to inspect the gears.
You could post an ad to find another complete gearcase or just a gearcase housing.

If I shouldn’t replace the skeg/fin, what good is it to inspect the gears? Isn’t the whole unit essentially worthless as it’s one unit with the upper housing.

Or if the gears are in good shape inside my broken skeg, would I just pull those parts out if I was to find a new skeg/fin and upper that had not so good gears?

[Author]

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