Johnson K-50 Pressure Relief Valve?

[Buccaneer]

I was searching through files to see if I had anything for the Johnson K-50
I’m working on, and found a one page PDF saved as "K-50 LU".
The diagram looks like my lower unit, with the exception of
the assembly that looks like some kind of pressure relief valve.
I don’t have this gizmo, just the "four bolt" plate that bolts
on half way up the tube.
What is it?
Thanks.

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Prepare to be boarded!

[Mumbles]

Exhaust bypass valve similar to ones used on the PO-15 motors?

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[Tom]

It’s an exhaust relief valve. Once underway,water pressure closes the valve, which diverts all exhaust underwater.

T

[Buccaneer]

Thanks for the replies. Exhaust relief makes
more sense than a water relief!
Don’t believe my 1950 PO-15 has
that feature either.

Prepare to be boarded!

[squierka39]

The early K-50 s had it, then they made the block off cover and later ones, like yours omitted it. Then, the later leg omitted the mounting for it. My K50 has the housing but no guts so it’s blocked off, starts and runs fine.

[Buccaneer]

Under the "block off" plate where the relief valve
would go, there’s also a hole drilled into the
cooling water galley. Not sure what the reason
for that was. With the cover on, the hole is blocked off.

Prepare to be boarded!

[squierka39]

Ok, here’s how it worked. There is an aluminum cylinder inside the housing. When the motor is stopped it drops down, gravity, and the exhaust can escape. Start the motor and get moving the water starts to flow by the vacu pressure system. Some water is diverted to the cutout pushing the cylinder up and closing off the exhaust opening diverting it down and out under water. Simple . Problem is it got gunned up with exhaust and can stick.

[Buccaneer]

Squier, Thanks for the explanation.

Did the motors with the
exhaust relief in the lower unit leg also have the exhaust
cut-out in the back of the cylinder? Or did the later replace
the troublesome exhaust relief valve?

Prepare to be boarded!

[squierka39]

They all had the hole in the exhaust housing. The hand operated lever was an option as best I can tell. I have some with it and some without all the way thru the line of K motors. But, under the carb in the exhaust housing elbo is a small relief that opens with the syncromised carbs. That is what replaced the leg relieve. Look on your Later K motor and you’ll see it.
The Lever on exhaust isn’t even pictured in the parts manual, I’m not sure how some motors got it and some didn’t.

[squierka39]

There is a K50 in the classifieds here. I’m not sure what year it is but it has the block off plate and the lever relief. I’m going to guess the lever went on the K-50’s that got the block off plate. Then when they came up with the under carb relief the lever became an option. The steering mount on the back is like that too, only shows up on some motors, not all.
Does your have the relief lever on it?

[Author]

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