Crank Case Breather

[stuck]

Gent's,

On my 4.6 (that was already squirted when I got the engine) the crank case breather is piped to a breather at the top of my snorkel rather than piped to the plenum.

Assuming that there is a good reason for this could someone explain it to me please?

Thanks,

Mick.

[FridgeFreezer]

They have two breathers, one is from the rocker to the plenum via a flame trap screwed into the rocker, the other is on the other rocker through a small mushroom thing, this has a tiny pinhole in it, the theory being the plenum sucks from one side and the other side trickles a bit of fresh air in. Depends which one they've extended really.

On mine I left the plenum-to-rocker one and tapped the mushroom one out for a push-fit fitting to extend it.

[bobtail84]

As FF has said leave the plenum-to-rocker one BUT.. put jubilee clips on all pipes to make sure you have no water ingress. The mushroom one was removed and made a bit bigger so when the engine was totally submerged there was enough air to stop the block being sucked down to an oxo cube.

[AncientGeek]

On some models the mushroom was replaced by a pipe going to the clean side of the filter. The one on the flame trap splits into 2 on models that I'm aware of. One goes to the plenum via a restrictor, the other goes upstream of the thottle plate. Its unclear which side you are talking about.

When using MT/MS you can see the effect of the plenum connection on idle vacuum by pinching off the plenum connector. Its basically acting as an oily air leak. The effect reduces as the engine is under load. I've often wondered if fitting a PCV valve would not be an improvement.