Bradysdad

I recently purchased my first C2, a 65 coupe with a 327 4spd. Enjoyed it for a few hundred miles and when I checked the oil, I was down 2 quarts. Not normal...was full when I brought her home!

Very soon afterwards, my engine started popping out of the right bank. Pulled the plugs and saw that #8 was completely gummed up.

I did a compression check and all 8 holes were in the 180 range. Not puffing under acceleration or start up. But I did notice there was some oil mist in my air cleaner and carb.

Long story short, on the older small blocks, there is a breather pipe which goes from the back of the block (by the distributor) to the bottom of the air cleaner, through a hose connected to a little diffuser/mesh filter in the air cleaner. This was pre-PCV valve days (solid valve covers). I pulled the hose going from the pipe to the air cleaner to see how much oil was moving through there and sure enough, within a few miles, my manifold was covered with an oil film.

Upon pulling the intake, I saw that whoever rebuilt the engine a while ago, did not reinstall the internal filter canister which sits under the intake and attaches to a hole in the block which is directly on the inlet end of the vent pipe I described earlier. So I was sucking raw oil/mist from the lifter galley, right into the carb through that top vent pipe.

In addition, I found that the little vent on the oil filler tube at the front of the intake manifold was connected directly to carb/manifold vacuum instead of to the bottom of the air cleaner housing . So I had a “double sucker”.

I am just getting the motor put back together after buying a new canister from Corvette America, but I am confident this will take care of my oil consumption and plug fouling issue. Hope this helps in case anyone else is losing oil...

DansYellow66

Good sleuthing - I would guess that should fix things up.

59BlueSilver

You never know what Bubba is up to!

SWCDuke

PCV valves were used on '61/2 Corvettes delivered in CA and all states beginning in '63.

The '64/5 system was "valveless", but Chevrolet went back to a system with a valve in '66.

The primary purpose of the PCV system is to prevent blowby, which consists primarily of unburned air/fuel from being released to the atmosphere, and because they offer better crankcase ventilation than the old draft tube, they went a long way in preventing sludge buildup.

There are no "negatives" performance or otherwise, as long as the system is properly designed (which is not always the case) and configured per a proper design.

The '64/5 system could flow both ways. Under light load filtered air passes to the rear vent, circulates through the engine and is pulled into the manifold via the oil filler tube vent to a restrictor attached to the carb. Under high load flow might reverse. The screen acts as a flame arrestor to prevent a backfire from propagating to the crankcase, possibly causing and explosion

PCV valves have a backfire feature build in - they only flow one way - and those systems also incorporate a flame arrestor screen on the fresh air inlet side.

Unfortunately many do no understand the purpose of the system or the different architectures, which is why you had the problem.

The best source for understanding the PCV system configuration is the AIM, although it does not show the liquid-vapor separator in the engine valley, which was installed at Flint. All other PCV hardware was installed at St. Louis, so it's in all the AIMs.

Duke

MikeM

There were several configurations, depending on engine. Which one do you have? I think all '65 engines used a restrictor of some sort in lieu of a PCV valve. You don't mention using either.

Doesn't sound like your plan will fix the problem.

65tripleblack

What kind of carburetor are you using? The original setup for 1964/65 used a fixed orifice fitting threaded directly to the manifold vacuum port of the carburetor. If you don't have it, a replacement PCV valve from a 66-67 SBC Corvette can be plumbed in between the "little vent on the oil filler tube" and the manifold vacuum tap on the carburetor (same diameter as the vent tube on the oil fill, and located on the carb base, usually at the rear) using 5/16" ID rubber vacuum hose.

For 1964-67, the direction of flow is: The crankcase is ventilated by suction out of the tube on the oil fill tube using manifold vacuum which is regulated either by a PCV valve or a fixed orifice. It is pulled directly into the intake runners and burned with the intake charge. In order to supply fresh air to the crankcase, filtered air is pulled from the air cleaner into the vent tube at the back of the engine block.

For 1962-1963 the direction of flow was the opposite way, and the vapor separator was critical.

You will have to adjust both the fuel mixture and the speed screw after doing this. The engine must be running like shlt with such a huge vacuum leak (if you have full manifold vacuum pulling from the oil fill tube with no regulation of some kind).

Bradysdad

Thanks for the feedback all! The engine was set up with no PCV valves anywhere (valve cover, vent hose, etc...). There was a vacuum hose directly from the base of the carb connected to the oil fill tube vent and the large rear vent tube going directly into the air cleaner. No internal canister for the rear tube.

The car did run like **** with the huge vacuum leak. With the idle screw all the way out, it wouldn’t idle less than 1200-1300rpms. I also had a huge puddle of oil at the base of the rear tube once I removed it, and as I said before, there was a lot of misting oil coming out of that back tube, getting all over the manifold.

I am using the stock Holley 600 carb. Once I plugged the vacuum leak, it ran great except for the fouled plug and oil consumption. I am hoping the internal canister fixes that.

65tripleblack

Holley means you have either a 327/350 or 327/365 and should be using a 2818 list number. The tomato can alone won't fix it. Either use the .010" metered orifice elbow that was used for 1964-65 or better yet, use a 1966-67 PCV valve substitute.

PM me if you need specifics.

DZAUTO

If you have an early block (56-67), then you need the canister under the intake manifold------------------------IT IS NOT, repeat, NOT A FILTER!!!!!!!!!!!!! It is an oil/vapor separator!!!!! It permits vapors to be sucked out of the crankcase and liquid oil to remain in the lifter valley.
REGARDLESS of early or late block, there has to be an inlet for fresh air----------------------and an outlet for crankcase vapors. ALLLLLLLLLLLLLLLLLLL early blocks with the crankcase hole in the rear of the block had a tube of some kind coming from that hole to either a road draft tube (pre 62), OR, a tube going to the air cleaner/PCV valve.
Also, the early engines had a breather cap on the oil filler tube which was the inlet source for fresh air. Then about 63 (depending on engine, carb or FI), the oil filler tube had a NON-breather cap and a fitting on the side of the oil filler tube for a PCV valve (or metered orifice). BUT, regardless of engine, carb or FI, ALLLLLLLLLLLLLLLLLLL 56-67 engines had an inlet source for outside air and an outlet fitting (either at the hole in the rear of the block, OR, a fitting on the oil filler tube). ONE location for in, ONE location for out, plain and simple. NOT, repeat, NOT two locations for out! The inlet and outlet were determined by the engine, carb or FI.
SOME engines, carb or FI, used the rear hole for inlet air (STILL NEED THE CANISTER UNDER THE MANIFOLD). There was a large tube which went from the air cleaner (carb of FI air cleaner) furnishing filtered air from the air cleaner into the crankcase, then a PCV valve (or metered orifice) connected BETWEEN the oil filler tube and a fitting on the carb base for MANIFOLD vacuum.
The inlet/outlet of 63 FI engines is a little different from other engines. The hole in the back of the block has a small tube going up to a PCV valve on the right rear of the FI plenum and a fresh air tube between the air cleaner adapter and the oil fill tube. Then on 64-5 FI engines, there was a big tube from the hole in the rear of the block to the air cleaner adapter and a manifold suction tube (with metered orifice fitting) between the front of the plenum and the oil fill tube-------------------------but still, one inlet and one outlet.
Thus, even though 63-65 FI setups LOOK the same, the air cleaner adapter for 63 FI units is totally different than 64-5 units.

64luke

I’d have guessed a can of STP in the crankcase would do the trick.

65tripleblack

No problem. PM sent.

EDIT: since cannot attach photos in PM editor, I'll post it here. The PV679 takes 5/16 hose on one end and 3/8 on the other. Use 5/16 hose on both ends and stretch to fit.