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PCV valve operation

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Hi all
I have a little problem with my pcv valve and wondering if anyone can assist.

the engine is a mild cammed 302, 600vac sec holley, P&P cast 351 heads, roller rockers, balanced bottom end...its probably around 320hp. Fun without being outrageous.

The car is still left hand drive and our registration rules mean it is not supposed to be least not in any way that can be easily identified! So recently i removed the Ford Racing rocker covers and replaced them with stock ford ones. I had to beat up the baffles a little to get them over the roller rockers, but now all looks pretty close to factory under the hood.

I got one of those d-shaped grommets and put a normal pcv valve venting back to the carb. With the old rockers, i just had a breather cap instead.

Now it seems the engine has enough action going on that it is actually sucking oil into the carb. I lost about a pint of oil on a recent spirited drive that involved 6 or so full throttle blasts 1st thru 3rd. the exhaust is black and caked and there are oil spots on the tail around the trunk and the valence.

its not leaks and its not rings, its definately going in via the pcv.

I thought the pcv "vented" the rockers by pressure from the inside rather than suction from the carb.

Any suggestions?

No, the carb connection from the PCV is actually sucking out the unburned fumes from your crankcase, and is burining it twice.   If you are getting oil that is being sucked into the PCV, then you have blow-by, and that is only caused by having the oil rings on your pistons not being set or worn out.  If you have just recently overhauled that engine, then don't race it until  5K miles until those rings get set.  If you have already raced that newly overhauled engine, then back off and drive it gingerly for about 5K miles, then try to race it.  You just have to know how to break in a newly overhauled engine. 

thats the wierd part...its not a new engine and its only had the problem since i put the pcv to carb connection in. with a breather on the rocker cover it wasnt doing it. i tried a different pcv and it made no difference.

its not a ring issue. its like it is sucking oil straight out of the rocker covers. the hose between valve and carb has oil in it. could the vacuum pressure created by the induction be enough to suck oil like that????

its not blowing clouds of white smoke, more some blackish smoke as if it were running rich.

  The operation of the PCV valve is supposed to stop just what you are experiencing, sucking oil. The carburetor draws in crank case fumes thru the valve under low engine operation. When you 'punch it' (American for extreme throttle), a plunger rises and is supposed to stop any gasses getting sucked into the carb. A spring normally keeps the plunger down, so, try another valve. You can clean them in solvent but that does not correct a valve not closing or completly seating. For a temporary fix, partially or completly block the hose to the carb. Also, consider 68 style valve covers that are taller and your baffles may clear.

thanks Jim,
i will try a different valve.

what you describe makes sense. I always thought that pressure under the rocker covers when you punch it was pushing the valve open, not closed.

i just replaced a faulty balancer so was keen to test the vibration...but if its going to suck the sump dry every time i sink the slipper then a plan B is going to be required. ;D


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