What size gear screw?

[jdentski3]

Hi

I am new to the forum. I have been getting some milky gear oil which I think is due to the fact that my gearcase magentic screw and vent screw are old and the gasket is rock hard. I am trying to figure out what size screw I need. I have a 9.9hp Mariner (I believe made in 1996). The gear oil drain hole fits a standard gear oil hand pump so I am thinking the size must be pretty standard between outboards. Does anyone know the size I need? Most of the ones I've seen online are 3/8ths. Thanks!

 

[Bondo]

Ayuh,.... Welcome Aboard,..... 3/8"- 16 is the standard fill/ vent size,.....

Merc sells the gaskets, which is where I'd start,....

The screws don't really wear out, other than the slot gettin' boogered up from slippin' screwdrivers,....

 

[Scott Danforth]

technically you are supposed to change the gasket every gear lube change (annual maintenance)

you may also want to pressure test the lower to see if you have a seal going bad (shift-shaft seal, prop seal or hub-carrier, or input shaft seal)

 

[jdentski3]

Thanks for the replies. I am going to change the screw and gasket just because the screws are starting to get stripped and the gasket feels like it has fused on to the screw. Once I change the screws I will keep checking for milky gear oil and get a pressure test if needed. Are the top and lower gear screw interchangeable? The top seems to be a similar size to the bottom but I haven't tried swapping them to see if they are an exact fit.

 

[Mohawkmtrs]

Both screws are identical.