Howdy,

Sorry, this is a really newbie question, but I'm trying to get this right. This is on a 1991 5.7 Liter EFI Mercruiser motor.

I had my starboard motor rebuilt. The machine shop gave me a set of gaskets with the motor. In the meantime, I had ordered a set of Mallory marine intake gaskets for the motor. The center water-jacket holes are not used on this motor. The Mallory gasket came with a little piece of metal to block them. The gaskets from the machine shop don't have a way to block these holes.

The problem? The Mallory gasket is cheap paper and I wasn't careful enough taking it out of the blister pack (I was actually pretty damn careful) and I broke it where one of the air intakes is. The machine shop gasket is some sort of rubber and seems MUCH higher quality than the marine gasket. It's thicker and heavier.

I'd like to use the rubber gasket, but I'm wondering if I don't plug that hole, won't it just seal anyway? I don't know why a piece of metal needs to block the water-jacket hole. Or, if I really need to use the paper gasket with the metal insert, can I just put some silicone over the broken part, or does it even matter since the break is where the air intake is and not the water jacket? Pics below.. and thanks in advance for any advice!!
Stan

Black one is the nice one - but no plug for the unused water jacket hole. Lighter colored one is the marine gasket with the plug:


A closeup of the break:

That is not a water jacket hole. That is an exhaust cross-over hole that is utilized with carb engines with the old spring-loaded choke.

Like he said.. That passage was used for carb choke control. As engine warmed up, the exhaust heat passing under intake would heat up a spring type element located inside the intake manifold. As it warmed, the spring would expand and react on the linkage controlling the choke, causing it to open. You don't need that on your set up. You can use black gasket as is, which will still allow the heat to pass under the intake, or you can get metal plugs that snap in place which come with that black gasket. Theoretically, by blocking off the passage, your air through the intake will be cooler with that blocked off. I'll bet the shop that gave you the black gasket has the plugs that came with it. Usually they come with the packaging.

They did actually give me little plugs, but they don't fit that hole exactly right. Notice there's a little rise in the upper left hand corner. The plugs are exactly square, and they're kind of odd too. I can't imagine how they would seal properly. I called a local marine shop and they have the Mercruiser gasket in stock, so I'm thinking I'm going to just buy it and use that instead. It's expensive for a gasket, but I don't want any problems after I build this thing. So the peace of mind is worth the extra $30. That being said - I am curious about using the metal plugs I got. Here's a pic:

You can use those. It's not a perfect seal anyways. Just slows down the flow of air. As for the pic, it's a two piece metal seal. One on each side of gasket. They clip together, and the metal prongs of one seal go through the other seal. Then you bend the prongs flat to secure them together.

This thread is just one example of why I think OSO is such a great site!

Got it. Thanks for the help!

Oh yeah, I couldn't agree more. The amount of help and advice I've received on here has saved me tons of time and money.