Merc Cruiser Shutter Valve Replacement

[jwowens]

I have a 1977 Merc Cruiser 228 and at least one of the shutter valves in the exhause is blown out. My manual says you have to remove the engine to replace the valve, but my local marine dealer says engine removal is not necessary. Which/who is correct?

Can I safely run the engine without the shutter valves?

What is their purpose?

Thanks.

 

[TilliamWe]

Re: Merc Cruiser Shutter Valve Replacement

Their function is to keep water from rushing/pushing back up through the drive and into the exhaust manifolds' exhaust chambers, and then into the engine. Volvo doesn't use them anymore. I operated my boat (97 Chaparral 21' cuddy W/Merc 350 Bravo drive) for at least two summers without them. Some say they don't even really work. i am not sure, the new style look like they would work exactly the way they are supposed to.
As far as pulling the engine, mine wasn't necessary, the flappers are in the top of my y-pipe. But your may be at the bottom of the y-pipe, I swear I have read that on here before that there is a year range or application that only has one flapper and it's at the bottom of the Y. I would remove your exhaust hose from the top of the y-pipe and see if that's where they are.

 

[HT32BSX115]

Re: Merc Cruiser Shutter Valve Replacement

The "shutters" are there to help prevent reversion of water from the Y-pipe exhaust on a V-8 or the exhaust "down" pipe from "sloshing" up into a riser and into a manifold and into an open exhaust valve.

Depending on where the previous shutter went and whether it's stuck at the bottom of the Y/down pipe, will determine if you really have to remove the engine to get to it....

So the short answer on whether you need to remove the engine is maybe.

Can I safely run the engine without the shutter valves?

That answer could also be maybe too!


REF: what TW said above about Volvo:

When I had the King Cobra installed in my boat mine were stuck open for many years and it didn't seem to make much difference........ I don't think you would want to run without them on a Mercruiser but many have........

When I installed the Bravo in my boat a few years ago, I installed new ones.

 

[jtmarten]

Re: Merc Cruiser Shutter Valve Replacement

To replace the shutters on the old, log-style exhaust manifolds (riser on the back of the manifold), the engine needs to be removed. On the newer style manifolds (center riser) they can be replaced without removing the engine.