The risk is water entering the exhaust system as a result of wave surge while at low RPM or engine not running.
The rubber flapper is no longer available by itself..... you must purchase the entire outlet..... and it is expensive.
You will see these offered via e-Bay occassionally.
NOTE: 250/270 outlet is a tad bit different from the 275..... 275 positions itself further AFT just a bit.
This allows for some of the larger props.
While I don't much care for this, there is an exhaust bellows available that incorporates a flapper within it.
It must be installed with the flapper hinge in the vertical position.
Dan, I think that the 242 refers to one of the Volvo auto models.
The Marine Volvo Penta OHC 4 willl be listed as; AQ XXX and so on.
If you have the auto engine in there, you may want to check and see if the camshaft had been changed to the Marine profile.
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