7.5hp OMC base gasket question

This topic has 5 replies, 4 voices, and was last updated 5 years, 9 months ago by fleetwin.

Viewing 6 posts - 1 through 6 (of 6 total)

Author

Posts
June 28, 2018 at 12:29 am #10383
adam1961
Participant
Canada Member - 2 Years
I am working on a 1957 7.5 Johnson. When I look in my gaskets for the 304314 base gasket, I have a few versions under that number. My main question is should the small circle right above where the water tube comes up, about 1/2" in diameter, be solid, or should there be a hole. If it is solid, it will force the water along the passage in the power head, but I would think that there would be a lot of restriction. I have attached a photo of one on a powerhead. You can feel a hole in the bottom of the block behind the above mentioned round area of the gasket.

Attachments:
June 28, 2018 at 12:38 am #78584
crosbyman
Participant
Canada Member - 2 Years
this should work
https://www.vintageoutboard.com/collect … de-1956-58

Joining AOMCI has priviledges 🙂
June 28, 2018 at 5:58 am #78594
Mumbles
Participant
The gasket in your photo looks like a ’59 and later 313065 gasket which has been slightly modified by being slotted on the left side. These gaskets for thermostat motors have a hole in them for the cooling water and aren’t open in this area like the ’56 – ’58 304314 gaskets are. I really don’t think it makes much difference which gasket you use as the water seems to find its way thru here easily. The hole might have been meant to be a restrictor to help keep the motor at a certain temperature, but I’m not sure. Even one BRP 313065 gasket I bought sure looks a lot like a 304314 gasket, and that’s in a sealed package!

Attachments:
June 28, 2018 at 9:45 am #78597
adam1961
Participant
Canada Member - 2 Years
Thanks guys,
I will likely open mine up a bit more in the outlet area. I can see why i would have two versions under the same part number, it looks like one may have been used in place of the other based on the packages shown above.
Adam
June 28, 2018 at 10:44 am #78599
crosbyman
Participant
Canada Member - 2 Years
this is what I used on a 56 7.5

Attachments:

Joining AOMCI has priviledges 🙂
June 29, 2018 at 2:34 pm #78667
fleetwin
Participant
US Member - 2 Years
quote Mumbles:

The gasket in your photo looks like a ’59 and later 313065 gasket which has been slightly modified by being slotted on the left side. These gaskets for thermostat motors have a hole in them for the cooling water and aren’t open in this area like the ’56 – ’58 304314 gaskets are. I really don’t think it makes much difference which gasket you use as the water seems to find its way thru here easily. The hole might have been meant to be a restrictor to help keep the motor at a certain temperature, but I’m not sure. Even one BRP 313065 gasket I bought sure looks a lot like a 304314 gasket, and that’s in a sealed package!

I’m with mumbles, I don’t understand why there are two different gaskets for these 56-present models. Yes, I realize the 59 and later models use a thermostat, but that shouldn’t make any difference. I can’t see the harm in using the gasket with the completely open passage on either version on this powerhead design. Using the less restrictive gasket would ensure no debris gets caught in the little hole in the gasket…Oh well, just one of the things I wonder about instead of doing things I should be doing….
Author

Posts