MS440 Tank Vent Valve What the Gold Disc Is

The gold disc on top is a sheet of sintered bronze full of open pores. The MS440 vent valve is the breather for 044 class chainsaw tanks: a black plastic body, a sintered bronze vent disc on top, a ribbed collar in the middle, and a snap base at the bottom, seated in the tank vent. The gold disc is the heart of the valve.

Why can it breathe but hold oil mist and water? Sintered bronze is a web of connected pores. Air moves through them freely, while oil mist and droplets are stopped at the pore mouths. When the engine heats up and pressure builds in the tank, it has somewhere to go, so the tank does not swell and the vent does not weep. When the engine stops and the pressure falls, air moves back in through the same pores, and the tank does not collapse.

Which machines does the MS440 valve fit? MS440 and 044 are the new and old names of the same saw, and this valve is made for that tank. The MS360, that is 036, and the MS340, that is 034, are commonly listed as common fits, but old machines wear their vent seats differently, so match the old valve size and the vent hole before fitting, or send a photo to confirm.

When should the valve be replaced? A sintered disc packed with oil grime means the tank cannot breathe, and the fuel cap pulls stiff. A cracked disc lets oil mist run straight out of the vent. A broken snap base will not hold. The disc cannot be washed and cannot be replaced on its own, so a fresh valve puts the tank breathing right again in one go.