VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 52/53 Chev Engine Has Blowby

Is it normal & what would be the cause for my 41 Chev with a 52/53 216 engine to have blowby? It's not excessive as I have not needed to add oil between oil changes (every 1,000 miles). But it does leave an oil film under the car from the crankcase vent pipe. Thank you.
John

Depending on the miles on the engine blowby was common for engines with between 50-75 thousand miles. Blowby is a result of worn rings and/or excessive clearance. Have you checked the vent pipe for proper operation? It could be plugged causing poor venting or excess pressure build up.

I'm no expert on blowby but I did notice today when prepping my crankcase ventilator pipe for a coat of new paint, I noticed a coating of heavy sludge on the inner wall. Blocking off one end, I tried blowing through it. Sure enough, it was hardly "breathing". So I cleaned out each of the 48 inner vent holes with a dental tool and soaked the whole thing in kerosene, then blew it dry. Now I can easily blow through it.
Like m006840 alluded, maybe oil suspended in the fumes had no where to go but down the pipe and onto the floor.

The vent pipe(Main "fat" part above the block is double wall. The inner wall contains oil return holes. They may have been or are plugged not allowing the oil to flow back to the crakcase.
Years ago they either replaced them or set them on fire so the sludge would burn out.
When properly functioning a bit of blow-by can be seen when engine is running with more coming out of the slots in the valve cover.

From your suggestions I think the amount of my blow-by is normal. But I will check my pipe to make sure it is not plugged. It's sometimes difficult to leave these small problems. A bit of oil on the floor is ok since it runs just fine.
Thanks very much.
John

All engines "breathe" due to internal parts movement, another cause that was mentioned earlier here is ring leakage which will occur from original start but as they rings bed in it does reduce and after an considerable mileage will start to increase with ring wear.
Tony

I have cleaned up vent pipes by soaking them overnight in gas.

Good luck, Mike

I've got it soaking in gas in an oil change pan overnight. Will blow it out in the morning.
John

My '40 216 has blowby through the vent holes in the valve cover, and it's not a crazy amount - only times it's really even noticeable is when you get out and run it <50mph for an hour or two, then stop and open the hood.

Completely normal. Especially if there is a lot og contimantion in the oil.

My engine has about the same amount of blowby as ClassicMechanic's so glad to hear that's normal. Thanks
John