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LM 318 noise / leak from intake manifold

Drfeno

Member
I have an older Silverton 31c with twin 318's. recently I started to hear what sounded like an exhaust leak on the port motor. (Last season I had a leak in the exhaust manifold gasket on the starboard motor which sounded exactly the same). This time, I traced the leak down to what looks like the intake manifold gasket on the inboard side of the engine. Its definitely where the noise is coming from, and I can feel gasses escaping. My question is since this is on the intake side of the head, a few inches downstream from the carb base, should it actually be leaking under pressure there? The motor runs fine.

Thanks

Dave
 
Well, after doing some more research, it looks like the leak I have is at the exhaust crossover port. I never knew about it. I can see a part of the gasket is missing. The leak is in the exact center of the manifold (from front to back), and in looking at some manifold gaskets, that seems to be where the crossover is. I saw a reference in a post that gives the part number of a manifold gasket that has the crossover blocked, and its blocked exactly where my leak is.

Thanks,

Dave
 
A cut piece of stainless shim can also be used to block open crossover gasket ports. Some intake gasket kits came with them or regulated via a hole diameter plates.
It's possible the manifold crossover itself plugged up if it's never been cleaned out.
 
Thanks, I was unaware of the exhaust crossover. it was confusing to me that gasses would be leaking under pressure from what seemed to be the intake side of the head. After researching, it seems there is some controversy over whether to block the ports or leave them open. Knowing now that its not a huge deal, I won't change the gasket for a few weeks. I have small kids, and boating season basically ends once they go back to school (2 weeks from now). I don't usually get hauled until mid October, so sometime in September I'll remove the intake manifold and see whats going on. These engines only run in warm weather, I don't usually run them too hard, I cruise at about 3000 rpm, which equates to about 15-16 kts or so. I'll put back whatever was there for gaskets (port blocked or not blocked) I want both engines to be the same.

Thanks
 
I won't change the gasket for a few weeks. I have small kids, and boating season basically ends once they go back to school (2 weeks from now).

What,..??..?? That's a hot gas, with possible flames, an Ignition source, right next to a carb fulla gasoline,.... BOOM,.....

Yer carb probably has/ had a choke stove to turn the choke off, which has probably rusted away,......

Do as ya please, but yer endangerin' yer family runnin' it as it is,......
 
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