In line 6 Exhaust - What are those holes for?

[Hoser762]

I have an old Grady White with a MC-165 inline 6. This is the old MC-1. Predictably, the transom needed replacement and now I'm ready to put the motor back in. Before doing so I need to install the exhaust pipe and where it connects to the gimbal, trough the transom plate, there are two 3/4" holes with o-rings below the exhaust opening, the hydraulic lines pass between them. The exhaust pipe does not cover them. A V-8 "Y" pipe would. Every manual I consult illustrates this but not one tells me what they are. Someone said they are for back pressure relief, but that leaves me thinking about exhaust venting back into the engine compartment and that can't be right. What are these and should I care?

Do I need to plug them? Am I missing a part?

 

[dubs283]

they are idle relief ports for exhaust cooling water for a v-8

verify they are not machined open to the outside of the gimbal housing, if the exhaust tube doesn't cover them then they shouldn't be

in-line engines of that vintage didn't require the idle relief ports, hence they aren't "open" and the exhaust pipe does not cover them

 

[Hoser762]

Thank you.