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Hi! Just registered here, I guess this is where the action is now. I kind of miss the old board layout. Anyway,
I think I may need a new PCV valve. The plunger is loose in the housing. I can see it fall up and down if I flip the valve assembly up and down. I was under the impression that the spring in there is supposed to keep the valve closed untill the manifold vaccum opens it up. Is that true?
My truck is not idling very smoothly, so that is what led me to remove the PCV valve in the first place.
If I need a new valve, can I get one @ NAPA or Advance Auto? If not I will contact AB linn or Memphis Equip.
THanks for the help,
Karl
Asheville, NC
1967 M715 all stock except winch from M35A2 6x6, custom front bumper and British black and green camo.
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Karl,
Welcome. The PCV valve is a check valve. It allows the gases inside the engine to be recycled through the combustion cycle. A straight hose would do the exact same thing. The PCV is installed to prevent the gases from going the other way. Such as in a backfire. To answer your question. Some are spring loaded and some not. As long as it opens and closes to the proper pressure it will work. Mine is also loose and rattles when shaken. I don't know if the specified one is spring loaded or not.
I would suggest a check of timing and carb cleanlyness for your idle problems. Also make sure that 1-5-3-6-2-4 is your firing order. The timing is supposed to be 5*BTDC. The balancer is graduated so getting right on 5 is very straight forward. Good luck
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Tim's kinda right. They do rattle when new. But a good rule of thumb is if in doubt, replace it. They aren't expensive.
The PCV valve is designed to be open during high vacuum like at cruise or when decelerating. It will close when the vacuum drops below a certain point so you still have sufficient vacuum for the carb to operate.
Direct vacuum to the crankcase is bad and will give the same symptoms of a huge vacuum leak when you accelerate or at other low vacuum times.
Chris
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Oh, yeah, about the timing - these engines will run (crappy, but run) with gross out-of timing conditions. A performance mod: These trucks were spec'ed to run of crap gas - 85 octane, I think. This is probably why the timing is so conservative. With modern commercially-available gasoline 87 R+M/2 octane), you can probably advance your timing to 8~12 BTD for a bit better performance. Just Doug, er, I mean retard it if you get any detonation.
Any thoughts on this matter?
