The Stovebolt Site Forums The Shop Area Engine Shop 1958 235 PCV Conversion

I have been doing smaller projects on "Thor" to try and make it more road ready. I have been fighting an oil leak after swapping to a standard large cap HEI, part of that I attributed to the lack of crankcase venting. I read the write up on Deve's web page and how he assembled his PCV system, I wanted to maintain more of the original appearance of the engine.

I removed the Road Draft tube, pulled the cap off the canister and cut the down tube off. I made a small plate that was tack welded over the side hole left from the down tube. I remounted the down tube and welded it back onto the canister. Like in Deve's description I added a grommet to the canister cap and reattached it. The rest was bending up a line and attaching a fitting to the intake manifold. I used a PCV valve for an '85 - '88 F@&d Ranger 2.3L as it crossed with the valve recommended by Deve.

A couple of evenings and a little paint and head stratching and the job was finished. I will admit the bends in my stainless steel line could be tighter but that will be a project for the 261 when I put it in "Thor".

I don't think you will be happy with that arrangement. The pcv valve is too low relative to the engine and will draw oil out of the crankcase.

Pcv systems require the valve to be up at valve cover level to avoid sucking oil out of the engine.

Craig, What are you doing for allowing air back into the engine? I think I would 2nd Otto's comment about the placement of the PCV valve. In this 2020 thread on the same topic there is a mention by HRL about the port being about valve cover height to prevent oil getting sucked out of the crank case. I believe there was another more recent thread on the subject, but not finding it just yet this morning. I need more coffee!

That looks good to me. I like your ingenuity. Great job!

Otto, the valve is mounted at the top of the existing road draft tube so it’s 6-8 inches higher than the crankcase.

Time and use will tell. I'm pretty sure there's a thread around here somewhere in which the poster describes the same conversion as Craig's with the valve on top of the tube and experienced significant oil loss.

The valve is still at crankcase level rather than at head level. Every engine with a factory designed and installed pcv system has the valve located at the top of the engine in the head.

Below is link to one previous forum thread which discusses 235 PCV valve installation and placement. Forum can be searched for many more.
PCV Valve

ol 55 - You found the one I was looking for. Thanks!

Is the oil leak associated with the new distributor? Which large cap unit did you use? About a year ago I explained how to convert a 230/250 coil in cap type HEI to work with the 235 and how to avoid the oil leak associated with them.

The valve cover uses a vented breather cap. The PCV valve draws between 1 - 3 inches of vacuum as described in Deve's post on his site. I verified the amount of vacuum with a gauge.

The Road Draft canister still has the internal oil screen. Being it is about 6 inches taller than Deve's system I suspect that it will at least draw less oil than that.

If anything this setup will certainly work better than a Road Draft tube. At RPM the top of the valve cover would get wet with oil from the breather cap.

The HEI was acquired from a friend that wasn't going to use it. The shaft was modified to work with the 235. It has a hold down that was actually made by HRL, he has told me as much. The problem is the shaft was not machined with the oil grooves as the original distributor has, oil migrates up the shaft and out the opening. The 235 block is machined with a well around the distributor hole to aĺow the original vacuum advance to move. The HEI mounts flush and doesn't close the opening. I made an aluminum collar that fits into the well, the shaft slides through the collar and allows the HEI to set flush with the block. The collar is set into the well using a light coat of gasket maker RTV, the HEI set flush on a gasket asusedon the GM V8's.

As a note, even a factory PCV system as ail baffel located in the valve cover...

I’m not sure why we need to go with stainless tubing on these, I used a piece of 3/8 copper soft I had around which bends up nicely with even a cheap Harbor Freight bender. I had my PCV located horizontal and lower (still 6-7” up from the engine), it did not draw oil but…it did have oil residue in it. Not to ignore HRL advice (never a good idea btw) I chose to relocate it to vertical and higher up.
This install has a corvette v8 oil fill pipe with outlet, and a rubber 90 degree hose from NAPA.
I took the air draw from the clean side of air filter to an oil filler cap and JB welded the valve slots.

Top of draft tube is basically what I had. Didn't see evidence of sucking oil but got tired of big ole draft tube and long line across to manifold. So plugged the DT hole and ran suction straight to the valve cover. (Vapors drift upwards don't they?) Anyways, much simpler and elegant-er, IMO.

When I converted the 230/250 (Chinese made) distributor to work in the 235 I used a round hacksaw blade to carefully cut an o-ring nesting place, filed it smooth and it has worked fine. What you did sounds like it would work also. They will leak there, though.

I had the stainless steel tubing left from another project.

.....did the conversion on my 261 and never had a problem......could some of the problems be due to the amount of pressure a particular valve had??

....looks good Tut, keep trucking brohter.

My current setup is PCV in a non vented breather fitted into the oil fill hole. PCV line routed to manifold from there. My makeup air is provided via a motorcycle pleated breather at outlet of tue draft tube. It’s all kinda ugly , but it seems to work.


My revision 2 plan is similar to Tuts, in some ways.

1) PCV hardline affixed draft tube. Plug draft tube. Route line around front of engine, as sneakily as possible…to the manifold.

2) Screw-in PCV valve into manifold Tee. A valve similar to what easy 283s used. Pipe thread on one end, and hose barb on the other.

3) Makeup air provided via more or less factory method. Clean side of air cleaner to valve cover. I’d like to locate a center fill valve cover. But I might just plumb a bulkhead fitting and baffle into the side of valve cover.

The GM PCV system was created for trucks working in a nasty and dusty environment. Originally it had nothing to with the Clean Air Act or laws in California. California air pollution got so bad that they enacted laws to address the problem. The program was Jan 1, 1964 through Jan 1, 1966. Most 1950 and later cars and trucks, in California, had to meet the requirements. The National Clean Air Act started around 1970 and was initially required on automobiles built around 1971. So, unless your 1958 truck came from California or is in the state of California, you don't have to have the PCV system (to my understanding which is always subject to correction). AC (AC Delco a GM subsidiary) created kits "CV" and "KV" plus 5/8" ID rubber hose to meet California requirements. Hotrod Lincoln was one who installed them (big Grin). I have the AC PCV catalog. Start with (http://www.gmpartswiki.com/getpage?pageid=226190) to get the Ventilator Assembly listing and nearby pages for various fittings and the valve.

What is the original PCV system for a 1958 Chevy truck? It is subject to interpretation, and I would have documentation to support having what you believe to be an originally equipped engine especially if you want to compete in an original truck showing.

GM modified the road draft tube (Ventilator Assembly) to accommodate the PCV valve at the top of the tube. The road draft tube has segments inside to trap oil mist vapors and drip them back into the crankcase. In my opinion this is the best location for the PCV valve. I can provide pictures etc. if you want the "original look" but original parts are hard to find.

The PCV valve you select is rated for a certain flow and you may need to use the correct diameter hose or pipes to not restrict flow.

Having put down my hogwash in writing, I have to say the systems of the 50's, 60's and early 70's are nowhere close to today's modern crankcase ventilation. The biggest advantage of the old PCV system is to blunt the hot burning oil smell from wafting through the firewall and stinking up the cab BUT the is the nuance or general experience of owning and old Stovebolt.

The owner's manual of my 1963 Pontiac Tempest specifically mentioned its engine having the PCV valve vs road draft, noting that crankcase vapors are 50x more concentrated in pollution than exhaust fumes. Everybody running that Pontiac four banger does the factory PCV conversion, which consists of a rubber grommet for the valve in the rear of the camshaft cover, then the valve and hose going to manifold vacuum. All three years had the steel wool filled ventilated oil cap so that could stay the same. PCV also provides a negative pressure environment inside the crankcase, which aids piston ring sealing. As well as greatly reducing hydrocarbons.. PCV was the cheapest, lowest hanging fruit that auto makers could pluck to begin compliance with US emissions laws. In addition to being a good idea in general.

1953 GMC Master Parts Book shows parts for "positive type ventilation" as far back as 1939 on larger than pickup sized models. Here is a picture from a US Army deuce and a half maintenance manual. This valve was fed from the top of the valve cover. Instead of being throw away, you can disassemble, clean and re-assemble.

The PCV did greatly reduce the oil smell in my cab. Thankfully, I still get the full old truck experience with the aroma of the thick layer of gear oil simmering on the transmission.

I would think that a closed PCV system for military vehicles were a must have for forging thru water.

This is what I did to my 235. I made a plug for the road draft tube and drilled a hole at the back of the valve cover. Vented oil cap in the front.

This is the PCV system on my 55 Grumman. I just assumed it was stock because I’m always next to (and sometimes in) the doghouse.

I bought a 261 that had seen duty in a 56 2-ton. It came with a factory PCV system and has the valve shown in the military TM. There are specs for the strength of the spring and instructions for cleaning in the 62 truck manual I have. The valve sits approximately at the bottom of the valve cover and is horizontal. The tube runs around the front of the head and is plumbed into the manifold along with the brake vacuum and other lines. I did not use the original valve cover as I have a Wayne repro aluminum one.

I used the vented and filtered filler cap for make up air rather than cut a hole in the oil-bath air cleaner. This caused the problem that at 0 vacuum blow-by comes out of the filler cap and gets drawn into the cab if you have a vent window open. Sometimes even if you don't.

Also it draws too much air and I couldn't get the idle below 800 RPM. I checked it with my unisyn and the valve cover sucks as much air at idle as either of the carbs. So I went back to the road draft tube. HRL suggested that I lap-fit the PCV surfaces which I may do when I get through my long list of other projects that must be done before winter. I hesitate to start over again with an experimental project till everything else is done.

More info on the WW2 era GMC PCV system.

Could a guy plumb the PCV inlet into the side cover somehow? Not sure what reason there would be to do that. If you did it just right, might be harder to see than some of our other contraptions.

I think Victor's PCV system is factory original, I have seen this setup in a few different manuals.

So far the only thing I have needed to to was adjust the air mixture on the carb, it seemed to lean out a little. I'll keep an eye on the oil consumption to see if it starts using any. The engine is tight and doesn't have much blow by.

Bill Hanlon's WWII setup is exactly what I discussed doing if I were so inclined to bother with adding a PVC system (which I am not) the last time this topic was brought up.
That is, using a down draft tube from an earlier engine which had the oil fill cap on the top of the draft tube and use a later model filtered cap.
You just need to plug the bottom end of the draft tube.
I also suggested having the PCV valve in or near the valve cover, and the source of vacuum at the wiper vacuum port on the manifold.