VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 crank case ventalation 1929 chev

I seem to have a vacuum / pressure problem with my 194
after 20 minute of idling (temp at 130f) Things get goofie
Engine will die down then speed up and or stall, fuel at times will drip out of carb.

I have rebuilt the carb, same response. Which got me thinking
where is the crank case ventilation? At times, tightening the valve cover down will also cause a stall.

Condition, I am rebuilding this vehicle, not sure on how these
29 engine performed. For example up from idle the engine shakes like it is off balance, is this normal? I had a crack in the clutch housing had it welded and balanced along with
the flywheel. (they are now a matched balance pair) The clutch and flywheel where 1.5 ounces out of balance. This improvement shows up at idle but the engine still shakes up from idle. Which brings me to think I have something else wrong? My last question is motor mounts, I used thick rubber and tied the engine down with a bolt and nut through the frame. The engine noise seems to be louder than I remember it, especially inside the cabin. Originally, only the front mount was present, What is used?

Finally what work can be done from the underneath with the oil pan off without taking the engine out again.
Note the 1930 manual shows a pipe connection from the oil filler tube to the carb, an item I am thinking of adding. Our 29 has no hole in the oil filler tube and the oil cap fits air tight? Which all makes me think i have a air build up vacum problem sourced to the crankcase. Any ideas,pleas e

If fuel drips out of the carburetor the float bowl is has too much fuel in it. Crud in the needle/seat, improper float level, fuel in the float are most common problems.

The early '29 has an oil separator on the back of the block and tube from it to the air cleaner. The later '29 block has the tube to the oil filler tube. Early has closed valve cover and no seals around the spark plugs. Later vents were put into the valve cover and seals around plugs.

The connection from the crankcase to the carburetor will have little to no effect on the running of the engine. Only with excessive oil mist from the crankcase can it change the way the engine runs.

There should be nothing between the metal on the engine mounts and frame. It bolts solid. Adding flexible material between engine and frame exacerbates the vibration.

1929 engines did not have motor mounts. The engine was bolted directly to the frame without any rubber.

The early 1929 engines had an oil separator on the driver's side rear of the engine with a tube that went to the air cleaner. With this system the flat valve cover was not vented. The venting was done around the spark plug holes in the push rod cover. The late 1929 engines no longer had the oil separator and the tube now went from the air cleaner to the oil filler tube on the side of the engine. The push rod cover was sealed with cork gaskets around the spark plug holes and the venting was done through three vents in the top of the flat valve cover.

If you are using a Viton tipped needle in your carburetor that could be the reason why the carb. is flooding.

Hi stan2,
I'm a 31 owner, so I may not relate to the 29 all that well. Anyway, that being said, the only problem your engine has is BAD GAS. That fixes everything. Goodby. If only that were true. When you demand power, BAD GAS is not fresh enough to perform. I do wonder though, how many cylinders does it take to maintain the engine just at idle? Are all cylinders firing? Pull one plug wire at a time to locate any dead cylinders. I thought that all 194 cid Chevy sixes had the combination oil filler/oil-air seperator ventilator tube. I also thought that the valve cover had air vent slits located at the top. Could these be plugged? Don't overlook a restricted exhaust system, although rare. If you don't have a ventilator/oil filler but just a straight tube with a tight fitting cap, try removing the cap, clamp on some steel wool for a temporary breather for testing. As for working with the oil pan removed, a general inspection (both looking and touching everything) and cleaning is about all I can suggest. Does the engine perform good when cold? You didn't say. Suspect rubber fuel hoses failing when hot, weak points/condenser and old wiring also. Keep us posted and good luck.

I ran an experiment on my 1930 Chevy years ago. I had only two cylinders on line (on purpose) and the engine still ran. It ran badly but it still ran.



Early 1929 194 engines had the ventilator tube going to the oil separator canister on the rear of the engine.



Early 1929 engines did not have air vents on the top of the valve cover.



Rubber fuel hoses were not used on the 1929-32 194 engines.

The float is dry checked it twice, I rebuilt with the rubber tip needle and seat. The fuel leaks out when the engine has been run for a long time and only when the air vacuum things shows up.

I set the float at 11/16ths as the book said, I agree it sounds like the needle and seat, the old one did the same and yet in a mouth blow test it passed with flying colors.

mine is early then - I will remove all the corks, the corks came in the gasket set, they where not their when I tore the engine apart, this could be my problem

thanks for the motor mount history, I will pull out the rubber
hopefully this will make it quieter

Still wondering how smooth these engines are to run, mine shakes when idling the engine up. Not like a miss fire like something is out of balance.

The engine had a rebuild sticker on it, best guess, 1943
the engine would have next to 2000 miles on it post this rebuild.

No blow by at all, piston and sleeves show no wear marks
Crank seemed very firm when I had it apart, so much so, I did not remove or touch any thing on the crank or cam shaft.

Fuel system as of rebuild
new fuel line
new fuel pump
new carb kit
new fuel tank
Gas 2 weeks old

Chipper wrote
The early '29 has an oil separator on the back of the block and tube from it to the air cleaner

never seen this on mine, but the air cleaner has a connection
which was not used. Would it be easy to miss the oil separator
on the back of the block? What dose it look like?

new resistive spark plug wires,( we have radio communications on board) new points and condenser but still using old dist cap, will try another cap and see what happens. Yes it runs well
when cold have adjust the valves in both modes cold by adding 2 thousands and when hot to 6 intake 8 thousands exhaust.

Throw the Viton tipped needle away and get a metal needle.

If you have an early engine without the vents on the valve cover then definitely remove the cork seals around the spark plug holes on the push rod cover.

If your engine is balanced it should idle as smooth as glass.

If your engine had an oil separator (early engines only) then you will have a large hole on the rear of the block on the driver's side. The later 1929 engines that did not use the oil separate had the oil separator hole cast over when the block was poured. In either case, you should have a ventilator tube attached to the air cleaner.

removed the cork, Huge difference! now I have an engine to work with. I suspect I have two very flooded Cylinders 1 and 2 are not firing. With the cork out the carb no longer leaks gas out
the engine and the idle screw can now begin to come off fully turned in. I might have cross firing the balance problem now seems to have moved. Ran out of gas, last evening,

With all the versions of ventilation, it would seem GM must have noticed a problem to account for the different methods?

Junkyard wrote
In either case, you should have a ventilator tube attached to the air cleaner.

Where should I connect the air cleaner to?
I don't have a vented valve cover
I don't have the oil separator

I had the flywheel and clutch balanced as a pair, no work on the crankshaft or bearings.

I have to regroup my efforts now, replace the oil, tighten down on the oil leaks valve cover etc, clean out cyl one and two with air, replace the dist cap and investigate the resistive wiring, and solder up yet another small leak in the rad that has devolved. then finally get more gas.

I can run the motor on any 2 combinations of cyl 3,4 5 6 but
as I said 1 and 2 are pretty dead. (hope there is no damage there) and re tool, new timing light will not flash, compression gauge will not fit spark plug holes, and i have to re-tune my ears for miss firings. Those cork things really threw me off base getting me started.

The air cleaner is connected to the air horn of the carburetor.

Since you don't have an oil separator, the ventilation tube goes from the air cleaner nipple to the nipple on the side of the oil filler tube. If your oil filler tube does not have a nipple, it has probably been changed since oil filler tubes without the nipple were used on the early '29 engines with the oil separator canister only.

Well I have two dead cylinders 1 and 2, and air bubbles in the rad water. Actually surprised on this as the barrels looked so fine the head looked fine. Next step for me pull the engine out again and see whats up. Thanks all for the info, well running on 4 cylinders corks removed it now sounds like a engine. Can't weight to try it again on all 6. Cheers all

Sounds like you might have a bad head gasket. If that is the case then you don't have to pull the engine.....just remove the head.

Hum, that is what it sounds like, we just installed a new gasket
copper type and everything seemed to fit nicely. I think I will take your advice and remove the head tomorrow. Anything beyond that will be over my shops abilities.

Let us know what you find.

Took the head off, the head must have been warped, cyl and two
leaked, then the big one, the top of piston number 1 lost it's top, cracked right off. above the piston pin.
Cranking over by hand had the remaining part of the piston going up and down, - leaving the top of the piston at the top? removing the piston top with a (Vacuum Cleaner) revealed the top ring of 5 had broken. Get this, the sleeve is still fresh as new.
We removed the engine in record time, placed it on a trailer
and it's off to our local outboard re-bore shop. Should be interesting what they find in measuring and if they have ever
seen anything like this before...

Well a year later I am back, piston one cracked in half.
now have a rebuilt engine, 29 head 30 block, and it is finally
running again. 1930 pistons, new rings, only cost $4,500
plus $750 for the 1930 block. But it runs.

Glad you are back on the road again Stan2.

My experence with cast iron chevy Pistons was in my 1939 sedan (family car since 1940). It came to me with 74.000 miles on the odometer. I rebuilt the engine and put new pistons in it. I kept the old pistond in the shed. At work we had a magnetic partical inspection machine, so a few years later i had the oportunity to Mag partical inspect my old pistons, and i found that all six pistons had cracks in the oil ring grooves , and one had crack extending down into the skirt area. My advice to anyone rebuilding an engine is to have the pistons Magnetical partical inspected if reusing cast iron pistons, or penetrant inspect them if reusing aluminium pistons.
There is a lot of inertia at the top of each stoke acting on the piston.