Reeds

[tlewick1]

What closes the reeds on a Mercury 1150 (1976-1978?) Is it just the air pressure? Because they seem pretty stiff and I don't see any mechanical feature which would close them.

 

[ondarvr]

They act like a spring and return to the closed position on their own, then the crankcase pressure pushes them against the sealing surface even harder.

 

[gm280]

Reed valves work like one way valves. As the piston goes down in the cylinder, it create a vacuum. That vacuum pulls in both air and fuel mixture and the reed valve fingers are sucked open. Then as the piston starts back up in the cylinder, it creates a pressure and that forces the reed fingers closed again getting ready for the spark. So those reed fingers do two things and they work very well for what they actually are.

 

[tlewick1]

From looking at it, it seems like they are already open and need pressure to close. However, you two are saying they are closed and are forced open. I guess I'll have to look at them again.

 

[ondarvr]

As they age sometimes there is a small gap, there shouldn't be, but it happens. Too much of a gap may cause problems.

 

[merc850]

There are thicker pieces of steel above the thin reeds called reed stops is this what you are looking at? They don't move.

 

[racerone]

When the piston is on the compression stroke a low pressure develops in the crankcase.---The reeds then open up and a fresh charge is pulled into the crankcase.----When the piston goes down on the powerstroke the reeds have closed from spring tension and now the crankcase pressure builds and that helps seal the reed valves closed.