Checking lower units with air pressure

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Bob D
Posts: 347
Joined: Sun Mar 15, 2015 4:52 pm
Location: Staten Island NY

Checking lower units with air pressure

Postby Bob D » Sun Aug 12, 2018 10:52 am

Does anyone know what the "official" air pressure is to check a lower unit?
I have seen numbers ranging from 5 to 10 psi, and there is nothing in the big red Johnson service manual.
Here is a picture of what I put together to check mine, after finding water in a newly rebuilt unit.
A Mikuni jet ski carb pop off pressure tool, and after many hours of looking, a CDI adapter. Be careful if you order an adapter from CDI they have three different thread versions. The one shown is the 3/8 X 16, which works for 50's OMC.
Bob D
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FrankR
Posts: 3766
Joined: Tue Mar 10, 2015 6:32 pm
Location: Florida

Re: Checking lower units with air pressure

Postby FrankR » Sun Aug 12, 2018 2:18 pm

One OEM manual that I grabbed at random suggests 3 to 6 psi,

Chris_P
Posts: 2624
Joined: Tue Mar 10, 2015 4:59 pm
Location: Hamilton ON
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Re: Checking lower units with air pressure

Postby Chris_P » Sun Aug 12, 2018 4:56 pm

I use 5 psi. I sometimes also check double lip seals at 10psi. Be aware, too much pressure can actually cheat a test, depending on lip orientation.


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