The Stovebolt Site Forums The Shop Area Engine Shop 235 strange draft tube

Hallo,
Im trying to identify how my vent system is supposed to work. Cant find any information on how it is supposed to work, only on the regular drafttube. And cant find any pictures of another 235 with the same setup either!? Has anybody else here seen this setup before?
Thank you/ Oskar

I have to say I've never seen a crank case ventilator that looks like that.

What year and model is your truck?

It is a 51 gmc but with what i understand a 58-62 235.
No i cant find any info or pictures of anything like it either

GMC trucks have a similar setup.

Ed

Oskar, is that a 261ci motor, looks like captains bars above starter. if it's a big truck may explain this odd draft tube cannister, lots of after market stuff got added back in the day, you can swap to original type tube if this set up doesn't function. If those three mounting holes are tapped for threads it's a passenger car motor, if no threads it's a truck motor fyi.
Best of luck

Looks like a 235, I dont see any captains bars.

That looks like a GMC standpipe to me. 235's had the downward-turned draft tube.

Wire brush the flat machined surface right behind the distributor and tell us what's stamped there.

There is also a date code right next to the dip stick tube and a casting number between the three bolt bosses. With that info we can tell you what you have...

Mike B

You may be saying 58-62 because that is when the oil cap was in the middle. Found one oil breather filter assembly on a 1956 GMC 270, pickup. Supposedly original. Found others on WWII GMC big trucks. Also a 1941 CCKW, 270 motor. These have a little different configuration. A piece is offset?? This is a stumper but a really neat accessory to have.

The casting number on the block is 3769716, heads 3836848
Above the starter is CON4 - L19D
I dont se any capten bars, i think its just dust/rust that makes it look that way.

How does the gmc standpipe work?

It seems to have a large lid with snap clips for the filter? and a screw cap for filling? Don't even know if it's an oil filled unit or not. Just a guess, open it up and let us see inside.
Hopefully the person who put it on there knew what they were doing because the valve cover cap is not a breather type and don't see any slots in cover. So how does your unit breath? Has to be open somewhere. Don't see where in the pics. I'm hoping it's not a mixture of the wrong parts for crank case ventilation.

When Chevy went to center valve cover fill cap and no slots, they had a breather cap. You don't. Maybe this unit takes care of the "in and out" ?

I believe bartamos is correct, early military truck, part of the fording system which includes a PCV valve connected to the intake and other components of a closed system.
Likely doesn't belong on that engine. Looks cool though.
Fred

Is there a hose on the carburetor side of the valve cover going to the intake manifold? If so, it may be the intake side of a PVC system. Inside the can with the clips may be an air filter, more than likely an oil bath type.

This is from a GMC truck. It should have a PCV to make it work correctly. The housing has a paper pleated filter inside, top cap is for the oil fill.

Joe

The PCV valve should be located in line with a hose that connects from the valve cover to the intake manifold where the vacuum advance is attached.

Here is a positive crankcase ventilator photo.

This is how the system is setup on the inside, sems like it lets pressurised air out thro the filter at a set pressure. The cap seal is dry, so it lets it out all the time now. No pcv system is attatched now, the valve cover has a npt plug in it. What pvc valve should it have? Installing it so it connects the valvecover to the plug in the intake below the carb?

For now the engine smokes like a steamroller thro the vent. It has been sitting for a long time i guess, hope that the rings will lossen up a bit while driven more. Trying to sort out everything from item to item. It runs now, but has a little rattle from time to time. So i think the lifters should need to be run a litle more too. Just waiting for a new radiator so i can run it a litle longer.

Thanks very mutch for al the input!

There was another recent post that showed a similar PVC design. That shows the suction line and PCV valve, from the valve cover to the intake manifold. [LINK]

1947-1954 Factory Assembly Manual
Engine Positive (Crankcase) Ventilation Instruction
R.P.O. 217 Section 0, Sheet 4.00
Two types:
Series: 5000
and
Series: 3000, 4000, 6000

The reason why the engine smokes could be because the crankcase is not ventilating.
To solve the smoke problem you could take the oil fill cap off and see if the smoking goes away or reduces.

In your photo, the pipe plug in the valve cover is where your suction hose for the PCV system will go. The other end will go to the intake manifold where the vacuum wipers attach. Finding original parts will be nearly impossible. The good news is you can find parts that you can use to make it work. The two ends are simply NPT pipe nipples with a hose connecting them. You’ll need to install a Y connector at the intake manifold to adapt the new PCV system into. The PCV valve could be installed in either end providing the direction of flow is followed. The tricky part is finding a PCV valve in the correct direction of flow (toward the manifold), that meters the proper flow of air so you don’t lose too much vacuum and enough so the system works. They make valves that flow in both directions. They are usually marked with an arrow as to direction of flow.

You must run a filter in that housing or every bit of dust that the PCV system draws in will be circulated thru your engine. Finding a replacement filter may be an issue. From your picture, I see holes in the bottom of the canister. I surmise the air would get drawn into those holes and then thru a filter, then thru the holes in the cap that gets clipped on top. If that is the case then a paper folded filter would not work. I suspect that it would be a more like the filter found in the original air filters where they use a media similar to course steel wool. After cleaning in kerosene, you would soak it in 30 weight oil, allow it to drip dry, them reinstall. Copper Or stainless steel scrubbing pads may be a suitable replacement.

You may consider changing to a conventional road draft system until you get all the parts needed to make your unique PVC system work. That way all you need is the road draft tube (Which is readily available on eBay) and a filtered oil fill cap on the valve cover, which you can find at you local auto parts store.

One more thing. Engines when you first start them up for the first time in years tend to smoke for awhile. You may find that the smoke dissipates a bit after being run for awhile.