I've been looking at breather boxes for a 1956 stroker I've built and come to the conclusion that a vent from fuel pump Blank and original oil breather in to this breather box will be fine.
So could I use an upright expansion tank into the fuel pump Blank with pipe from OG breather in to the tank. On the top can be small filter.
Screenshot_20161210-003637.png
Would this work?
I'm not keen on venting rocker covers as the pressure isn't created there so makes more sense to vent at fuel pump Blank
Opinions please. Be kind
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atlime wrote:I'm not keen on venting rocker covers as the pressure isn't created there...
What you're overlooking is that with each revolution of the crankshaft, crankcase gasses have to rush back & forth between the opposing pairs of pistons. The instantaneous overall volume of the crankcase varies some due to the difference in piston dwell time near TDC compared to BDC, but essentially it remains the same - however, a volume equal to half of the engine's displacement is constantly on the move.
The only routes available for gasses to pass back & forth between the front of the crankcase and the rear are through the area under the cam/above the oil and through the two small cutouts in the center main web, or up and down the pushrod tubes. It's that last path which creates the pressure pulsations that eventually fatigue the valvecover gaskets to the point of leakage. With a counterweighted crank spinning around, the openings in the main web are occluded much of the time - effectively it creates a primitive labyrinth seal - which exacerbates the issue.
More oil gets thrown up by crank windage into the left rockerbox than the right so some folks don't vent the LH valvecover (personally I've never had a problem with venting both but you may, assuming you aren't always turning left).
Venting via only the stock pedestal and fuel pump openings has more effect on the volume between #2 & #4 than it can on the "front" of the crankcase - adding a vent hose or two to the valvecover(s) - preferably at the forward end - addresses that.
The fuelpump blockoffs I've seen only allow for a ¼NPT fitting, which doesn't provide a great deal of "ventilation" - arguably not enough to justify running another hose. But if your breather box has enough connections, why not?
Some of my race blocks came from L-Jet motors which have no place to mount a mechanical pump - I considered drilling/tapping them for a fitting, but I never found it necessary. However, I used ¾" hoses off both valve covers and the filler can, having found ½" to be inadequate for my application. If you'll be running ½" vent hoses that might justify the fourth one, I suppose.
The stock pump provides adequate supply for most engines/applications and it doesn't hurt anything to leave one in place for a backup in case the electric one should fail (just connect the inlet & outlet pipes to keep dirt out) so you might consider doing that rather than using a blockoff plate...
