The Stovebolt Site Forums The Shop Area Engine Shop PCV system

Do one of you have a shop manual photo or illustration you can post of the PCV system used on 228-302 GMC engines? A Chevy system would probably be the same. Thanks

Will this work?
[img]http://www.directcon.net/gmc248/EngView.gif[/img]

Tony, notice the oil bath breather/oil fill tube where the road draft would normaly be. All of these various oil fillers and breather tubes interchange more or less Chevrolet and GMC.

and the actual PCV on the 228 [least on my ol 46] is the copper tube from the top of the valve cover to the base of the carb, which may be almost visible in the righthand illustration above [tho may have changed on 248]

Bill

Thanks for the illustration, now can you enlarge it? Ok, so what you're saying is the PCV valve itself is located on the valve cover and the road draft tube ia converted into an air intak breather?

you got'er - the "valve" on the carb line was a wee little thing right at the end of the tube that must have been the simplest one way gate thingie, and the cap on the road draft replacement/oil filler is like the later 235 cap that has the hokey steel wool packing in it

ya makin pcv's fer yer other ol inliners?

Bill

My breather tubes are oil bath filters. They don't have the dry element mesh. Pretty high class.

Note this is different than the Chevy setup where the riser part of the road draft was retained minus the draft tube and with a threaded boss from which the tube routed through the pcv valve and then over to the intake. The better setups used the air cleaner to replace air removed from the crankcase, although the vented oil filler cap on the rocker was also used. These tend to get blocked off with gummy grit and grease fairly soon.

I made up PCV systems for my 2 261 Chevys. I use a PCV valve for a later 250 6 in the valve cover, and retained the breather at the front of the valve cover and plugged the road draft tube.So the system is just like a 250 engine, a Chevy 6 is a Chevy 6.
Anyways,it works great on the stock 261 in Joys truck but on my hot rod 37,some oil get on the valve cover from the breather.I run the 37 hard and the breather must be marginal.I will us a length of 1-1/4 tubing with a K&N breather to press in the road draft hole in the block, then use a non vented cap on the valve cover.I'm assuming here the GMC or Chevy system uses a non vented valve cover, right?

Valve cover is non-vented, except for the PCV tube..................which does have a PCV valve attached at the manifold end.........there is a 90 at the manifold and the PCV valve threads into. THe tube attaches there and goes to the valve cover.

Sorry the pix are so small....I still have the manual, but no scanner .
Look closely and you will see.........
Someone else on the boerd did what you say.....except he posted pix of using a "freeze plug" where the road draft goes and put the PCV in the center......I don't remeber what valve cover he used or what type of oil cap/breather cap he had on it.........

If someone reading this is the user I am referring to, please post!
Sorry I can't remember the name :o .

Tony, I think the best setup if you don't the deluxe gmc oil bath air breather/fill tube would be to tap into your air cleaner. A lot of air cleaners already have this outlet, and if you ever had blowby it would still end up being burned. There is a flame arrester included in most of these setups. The breather oil fill cap on the rocker cover is really prone to get gummed up, plus suck dust (marginal filtration) into your rockers. Just my two cents/

I hear ya, but I don't know about another pipe on the engine,pretty soon it'll look all cluttered.
I did my usual minimalist approach,took a road draft tube, cut off the tube right at the main body,rotated the tube 180 degrees, welded it together,then cut the tube off a few inches higher than the main body.Now I'll make a small breather filter, either buy a K&N or something like that only cheaper and attach it to the tube.

I've got a later Chevy rocker cover (early sixties?) which has a hose connection at the back to hook to the air cleaner. This one has not vent slots. It came with a oil fill/breather cap which was like a pepper shaker, full of rust. The air cleaner is definitely a batter place to get "makeup air."

Thanks Ralphy,that one has the opposite flow of what we been talking about.I don't know,but I figure the PCV valve should be at the highest point on the engine ,as water vapor rises? And it's more likey to be sucked out? More modern engines are like this maybe from design or just economics?