The Stovebolt Site Forums The Shop Area Engine Shop oil breather cap fro 235ci

I have removed an aftermarket PVC canister filter from my 1962 235ci and plugged the block with a 1 1/4 inch diameter expansion plug.

Do I still need to vent the engine? If so, where can I find an oil breather cap (sometimes called a vented oil filler cap?)?

Thank you,

You need boht a vented cap and a road draft tube. The plug you put in the hole will have to come out to allow the draft tube to be installed.

I'm pretty sure what I took out was this draft tube you speak of. However, I'm 95% sure that would have been an aftermarket item in '53. My other truck ('54 GMC with a high pressure 235ci) did not have anything in place of the expansion plug; just the original plug. It didn't even have one of the aftermarket oil filters one sometimes sees. So, although it might be ideal to have some type of PVC cannister filter or a draft tube, what is actually necessary? I'm hoping a vented oil cap will suffice, but I'm definitely open to clarification.

Can you post a few pictures of what you removed? If it was a PCV system, it had tubing/hoses from it to some other location.

Usually the non-PCV 235s needed a vent above the head/valves - either slits in the valve cover or a vented oil-filler cap. They also needed a "bottom" vent, the road draft tube. Just as Bill suggested.

I'm sure it will become painfully obvious but web design is really not my bag... but here goes nothing:

http://gallery.wiesenportz.com/index.htm

On the 53 photos, it shows a modified vent tube with a hose attached. If you plugged that hole, you should still have a vent tube.

I believe the cab overs had a pcv system but I would have to do some digging to be sure.

I think what needs to be addressed here is why do the engines have a draft tube...or PCV.... or valve cover vented cap...etc.

It must be remembered that when an engine is running some hot combustion gas will leak by the rings.... no matter what.... particularly if the engine is worked hard and /or tired. Without a opening somewhere things are going to blow as the fumes accumulate inside the crankcase. On a well worn engine it is not unusual to see blue smoke pouring out of the bottom of the engine ( old style draft tube) almost at the same beat as the engine cylinders are firing..... sort of a chug chug chug of smoke.

Just having a small vented cap on the valve cover would probably not suffice to venting all the fumes.

The old engines used cut out slits in the valve covers do draw fresh air into the crankcase and the fumes where sucked out the draft tube as the vehicle moved forward.

Eventually manufacturers.... somewhere around the beginning of the WW II realized that in adverse driving conditions (North Africa) too much dust/abresives were sucked in the engine and greatly increased wear. Early 1940 GM military 216 were issued with the slit vented valve cover and old style vent pipe... soon to be replaced with a PCV valve, no open draft tube and a medium size oil air filter on the valve cover to allow clean the air to be sucked in the crankcase. The process was critical in making military vehicles water proof for beach landings. During landings, for short periods, they would close off the air intake on the valve cover and let pressure build up in thc crankcase pushing water out of any leak area. Immediately after landing they were told to open up the air intake to the crankcase...

The PCV... Positive Crankcase Ventilation valve... is a system connected to the vacuum side of the intake manifold and maintains a slight positive (vacuum) sucking of the crankcase fumes back into the combustion chamber.....

Later on (1955+), the PCV was refined and the valve cover became vented by a large 1 inch rubber tube that drew fresh air by being connected on the clean side of the engine air filter.

I would not advise running your 235 with out a properly connected PCV connection as you may cause oil leaks, damage gaskets and probably build up sludge faster than normal. You will still need a vented valve cover cap.. the ones with the metal fiber inside to trap dust..... the metal fiber inside the cap should be washed in gasoline and oiled with fresh engine oil at every oil change.

From your picture, you still have the PCV on the engine.... take it apart and clean out carbon/oil that may have build up....(carb cleaner solution works good) don't break it or loose as they are hard to find. The early steel type as pictured will unscrew apart for cleaning.... watch the sping and plunger inside.... you may want to replace the rubber hose with a nice clean 3/8 steel brake line right up to the manifold connection using a simple flare.

If you do happen to need a new one.... the only source I know of is from the parts suppliers for old WW II Jeeps such as Peter De Bella ... they are worth about $25.00

My 5 cents worth...

Bob C.

On the photos of that motor, there doesn't seem to be a PCV valve anywhere. If that is the case, I would suggest correcting that situation. All motors in normal circumstances need to have a source of fresh air for the crankcase. I believe the draft tube and filter/oil cap was used for most of the 235 production run. We had a 1960 Pontiac with a 261 and it came from the factory like that.

Bob,

Thank you for that excellent detailed reply. Very useful and ultimately convincing!

I will simply cleanup the PCV device, reinsert it into the block, put on a new hose and connect that to the existing stub on the intake manifold.

One more question on this topic: Will the PCV device increase vacuum or possibly decrease it?

Thank you,

Here is a description of the PCV system for the 1954 trucks. Does your engine still have the hose from the air cleaner to the valve cover? There needs to be a complete circuit for the ventilation flow.

The link is from Tim's wonderful site.

Hoyt,

Excellent reference!

I can see now why there was that extra "thingymabob" on the carburetor's oil-based air filter. My truck was indeed missing this last link along with the outlet in the valve cover.

Chalk up another learning experience.

Thank you,

Hi Scout

The vacuum readi9ng should not be affected by a properly functioning PCV......

Remember... if you do a vacuum check on your engine make sure you connect your vacuum guage directly to the manifold and NOT to the vacuum line on the carb used for the advance..... ask me how I got a headache using the wrong connection.... until I read of my mistake on the Forum....

Good luck !!

Bob