235 oil catch can

[wspringerjr]

I installed an oil catch can after replacing my road draft tube with a pcv valve. I was curious to see how much oil was entering the intake so I installed a catch can ( glass jar )to see how much oil was pulling into the intake. After 317 miles I measured 7 ounces of oil in the jar from mixed highway driving to interstate speeds of 65 - 70. Does this seem like a normal amount of oil for a pcv system? Engine is not worn maybe 2 years rebuilt.

[dwcsr]

That's a quart every 1300 1400 miles so its a lot. How did you do the PVC, freeze plug in the block hole and run a line to it?

[mr48chev]

I've seen a few around here that have the down tube cut off the road draft tube about an inch or so from the baffle piece that fits in the block with a grommet pushed in the piece of tube that is left for the pcv valve. That gets the pcv valve up away from any splashed oil in the crank case.

[wspringerjr]

My road draft tube did not fit tight and leaked a lot of oil. I removed the road draft tube and inserted a grommet into the block and inserted the pcv valve into that. Ran a hose to the wiper outlet on the manifold and put in a black pipe T. The catch can is 6 inches away from the intake port.

[mr48chev]

I'm not sure if there is some sort of baffle plate below that hole in the block to deflect oil and just let fumes by. That much oil getting drawn up there seems excessive at any rate and if it isn't being picked up from splash in the block it may be from blowby pressure in the crankcase due to worn rings.

[dwcsr]

That is the problem. You sucking air right past the spinning cranks shaft. There is just a plate in the block and you need to have a baffle like the larger portion of the draft tube to snag the passing oil and let it drip back into the case.

http://chev235guy.blogspot.com/2014/10/235-pcv.html

this site has goo examples. You may be able to stretch out the old tube to fit securely

[OrrieG]

Did you add a breather else where, like the valve cover, so you get air flow thru the engine and are not creating a vacuum in the engine that pulls out the air/oil vapor? For instance on 350 sbc there is usually the pcv coming off one valve cover and a breather on the other.

[mr48chev]

The top photo in the link Dave posted in post six is what I have seen guys around here do. I'd agree that you need a breather cap on the top of the valve cover but it should already have that.

On V8 engines with cheap aftermarket valve covers I have had the pcv suck oil because there wasn't a baffle but they sell those baffle grommets for those. Like this https://www.summitracing.com/parts/mor-68775/overview/

[wspringerjr]

I have a breather cap on the valve cover.I used Dave's tech tip to install the pcv valve. The only thing I am missing is the baffle. Thanks for the link. I will order this today.

[mr48chev]

It shouldn't take long to see if it makes a difference.

[whitedog76]

I haven't had a 235 opened up in a couple years. But if my memory serves me, there was a baffle and steel wool like material in mine. I wonder if yours is missing.

With that being said, I've always thought the PCV off the draft tube was a bad idea. I think drilling a hole in the valve cover and adding a PCV along with the breather would work just fine.

Another thought is using a large, like 1/2" hose and routing it straight up, so oil can drain back into crankcase and let the fumes pass by.

[mr48chev]

[QUOTE=whitedog76;7644 I've always thought the PCV off the draft tube was a bad idea. I think drilling a hole in the valve cover and adding a PCV along with the breather would work just fine.

.[/QUOTE]

Since the road draft tube was designed to vent the crankcase (PCV meaning positive crankcase ventilation) The system actually works better with the pcv valve placed at the old draft tube location.

The idea is drawing the fumes from any blow by or other engine process in the crank case. It works with one on each valve cover of a V8 because the air is drawn in though the breather on one valve over through the crank case and out the pcv on the other crank case. On later sixes that do have it on the other end of the valve cover I wonder if this is one reason we are alway fighting oil leaks on them as we may not be getting the built up pressure out of the crankcase well enough. You get air drawn in at the front breather across the top of the rockers and out the Pcv but are you evacuating the fumes well enough?

[whitedog76]

Here's some food for thought. What about using a long piece of pipe on the draft tube and turning it into a breather. Then add the PCV to the valve cover.

[wspringerjr]

If I'm not mistaken some of the GMG trucks have that filter on the draft tube location. There is a guy on the Stovebolt site that ha s that setup on a 54 GMC suburban. I bought a piece of 1 inch conduit today to make a stand pipe where the draft tube was. I need to raise my pcv valve off the block away from the splashing oil. If your idea is used then the vented valve cover would need to be closed to draw from the vented stand pipe, right?

[mphudak]

Here's one of the GMC road draft tubes w/the filter. IIRC they were available on the 302, not sure about the 270.



Good reference on the PVC conversion from jalopyjournal w/a few imbedded links
http://www.jalopyjournal.com/forum/t...t-tube.253006/