moorepower Posted March 23, 2015 Share Posted March 23, 2015 Hi guys, I've got a '61 impala with an internally stock 283. Recently I replaced my stock 2 barrel and manifold with an Edelbrock performer manifold and 500CFM carb. The result is fantastic and the engine is much more responsive. One issue is when I took it for a blast down the motorway the breather cap on the oil fill tube came off. Luckily it ended up inside the engine bay. When I stopped I bent the two prongs out on it and put it back in its spot. On the way home, it came off again and this time I lost it for good. My understanding is that the air gets sucked through this tube, down through crankcase and is sucked up through the PCV valve and into the carb, with the fumes getting burnt in the combustion process. Im not sure if the viabration has sent it loose or if there is a build up in crank case pressure? How do I test the PCV valve is operating? BTW ive got stock script valve covers without any breathers on them. Has anyone had similar issues? Cheers Luke Quote Link to comment Share on other sites More sharing options...
AllTorque Posted March 23, 2015 Share Posted March 23, 2015 Hi Luke, Welcome to oldschool. If you pull the pcv valve out of the rocker cover with the engine running you should feel vacuum if you put your thumb over it and feel the valve close. Where is the pcv hose plumbed to? It should be below the carb or to an intake runner. Also, please start a build thread for your impala. Keen to see pics. Quote Link to comment Share on other sites More sharing options...
cletus Posted March 23, 2015 Share Posted March 23, 2015 does it have a pcv valve? i thought the early ones had a draft tube that hangs down by the bellhousing. 1 Quote Link to comment Share on other sites More sharing options...
moorepower Posted March 23, 2015 Author Share Posted March 23, 2015 Cletus, you could be right. Im not that clued up on these motors and these are the first mods I've done to it. There is a 3/8 hose which runs from the bottom of the carb to a brass tee, which has a 1/4" transmission vacuum and a 3/8" hose which runs to a fitting into top of the block behind the distributor. I only assumed it was a PCV. What difference would a draft tube make? Could this be causing excessive crank case pressure to blow the breather cap off the filler tube. Could the increase in air flow from a 2 barrel to 4 barrel cause more blow by if the rings are slightly worn? (Which they could be. Im unsure on the history of the motor as its a recent Nevada import) Quote Link to comment Share on other sites More sharing options...
SOHC Posted March 23, 2015 Share Posted March 23, 2015 Could the increase in air flow from a 2 barrel to 4 barrel cause more blow by if the rings are slightly worn? (Which they could be. Im unsure on the history of the motor as its a recent Nevada import) I would say this would be the case. A friend put a nice big carb on his old 350 and the result was a split bore from the engine having to compress more with thin rusty old bores Quote Link to comment Share on other sites More sharing options...
moorepower Posted March 23, 2015 Author Share Posted March 23, 2015 I better cruise it to beach hop then. I shouldnt have an issue as long as I dont try to set a new land speed record. I have the intention of getting a 327 or 350 in the future, and put this carb and manifold on it. Dont need big horsepower in this car, just reliability. 1 Quote Link to comment Share on other sites More sharing options...
tortron Posted March 30, 2015 Share Posted March 30, 2015 I can answer your draft tube question is basic. Just a tube which runs from the valve/tappet cover down below the engine. Typically then curves a foot or so back and runs along side the chassis rail or gearbox. Used to vent crank case fumes out (wouldnt want to suck them back in for emissions and dirty up your plugs now would you) when driving, the air moving past the opening creates a vacuum and sucks the fumes out from your tappet area. (try this with a straw and a bowl of water if you like, blow against the end and the water should rise) this is also why if you have a bit of a worn engine you end up in a cloud of smoke when stopped at the traffic lights in order to function 100% the tube must be clear of gunk - clean with kero once a year. And - your filler cap must also be clean. Mine have a built in mesh filter to clean the air that flows through. Some tappet covers also have vent holes in them, though im not convinced they are of any use Quote Link to comment Share on other sites More sharing options...
tortron Posted March 30, 2015 Share Posted March 30, 2015 And as for the filler cap blowing off - pressure out the cap, or excessive smoke (a little when you shut off the engine is normal) is a sure sign oof exessive blowby. Leakdown test is probably a good idea, then consider your options regarding rebuilding or replacing (though i have heard of it on highly tuned high reving flatheads, where the crank moves fast enough to increase crankcase pressures enough to pop it off. Probably not.your issue though) Quote Link to comment Share on other sites More sharing options...
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