The Ford Barn

Flathead Fever · 06-28-2023, 11:35 AM

I was a licensed smog check/fleet mechanic here in CA for 30 wasted years of my life. If the engine is worn you "do not" want to install a pcv valve just leave the road draft tube alone and drive it. On an engine with excess blowby the pcv will with suck in the blowby along with oil and coats the intake valves. It will continue to get build up on the valves creating hard carbon until there is so much of it the air can barely flow into the cylinders.

If the engine is sealed the PCV valve should suck a piece of paper down against the fill tube at idle unless the engine has too much blowby, too many air leaks in the crankcase, the valve is defective, or the hose has collapsed. You must use a hose rated for gas or it will quickly become spongy from the oil and gas fumes and collapse under the vacuum. You could have an intake leak but it would idle poorly. You can run propane around the intake and carb base to check for leaks, The idle will change when the propane passes over the vacuum leak. Pull the hose out the valley pan and make sure it is sucking. PCV valves are calibrated for the size of the engine, you could have a valve that is a little too small. I've never installed one on an engine that never had one, but I imagine you would choose one from a similar size engine like a 1968-1970 Ford 302, that should be close enough. They generally last 30,000-50,000 miles before the spring loses its calibration. They should be replaced at that interval, but nobody ever does it until they fail and the engine won't idle.

You want the incoming air to the breather to be filtered otherwise your pcv valve is sucking dirt into the engine and doing more harm than good. Normally a factory pcv would be located on one valve cover and the breather on the opposite side so fresh air is pulled down into the crankcase back out the opposite valve cover flushing out all of the blowby gases to prevent the oil from getting contaminated which creates an acid. The breather would have a hose going to the inside of the air filter housing where the air has already passed through the filter. There are times when the pcv cannot handle all of the blowby., then it goes out the breather and into the air cleaner housing where the engine burns it. This prevents it from escaping into the atmosphere and creating smog.

If you suspect air leaks in the crankcase, I've never tried it but You could put a hair dryer on the fill tube and check around the engine for air coming out. We had a smoke machine at work that used heated mineral oil for testing evap systems on vehicles with charcoal canisters. If you have ever had a car fail the evap test and it wasn't the usual bad gas gap that is how you find the leak. You fill the entire gas tank and evap system with smoke and see where it comes out, it stinks the hole shop up. There is a good chance on an old engine it is tired and then I wouldn't worry about it and just drive it. PCV valve on a worn engine is going to suck up the excess blowby along with oil and it will coat the valves which will turn to a hard carbon until there is so much of it on the valves the air can barely flow past it.

You can do a compression check on the engine and then repeat it with a couple squirts of oil in each cylinder. If the compression comes up the rings are worn.

I have early cars with no pcv valves, and I don't drive them that much. I just change the oil when it gets slightly dirty. If you are building a new engine and want to install a pcv valve you can otherwise I wouldn't worry about it on an old engine.

06-28-2023, 11:35 AM	#8
Flathead Fever Senior Member Join Date: May 2010 Location: Yucaipa, CA Posts: 1,100	Re: Evaluate my PCV system I was a licensed smog check/fleet mechanic here in CA for 30 wasted years of my life. If the engine is worn you "do not" want to install a pcv valve just leave the road draft tube alone and drive it. On an engine with excess blowby the pcv will with suck in the blowby along with oil and coats the intake valves. It will continue to get build up on the valves creating hard carbon until there is so much of it the air can barely flow into the cylinders. If the engine is sealed the PCV valve should suck a piece of paper down against the fill tube at idle unless the engine has too much blowby, too many air leaks in the crankcase, the valve is defective, or the hose has collapsed. You must use a hose rated for gas or it will quickly become spongy from the oil and gas fumes and collapse under the vacuum. You could have an intake leak but it would idle poorly. You can run propane around the intake and carb base to check for leaks, The idle will change when the propane passes over the vacuum leak. Pull the hose out the valley pan and make sure it is sucking. PCV valves are calibrated for the size of the engine, you could have a valve that is a little too small. I've never installed one on an engine that never had one, but I imagine you would choose one from a similar size engine like a 1968-1970 Ford 302, that should be close enough. They generally last 30,000-50,000 miles before the spring loses its calibration. They should be replaced at that interval, but nobody ever does it until they fail and the engine won't idle. You want the incoming air to the breather to be filtered otherwise your pcv valve is sucking dirt into the engine and doing more harm than good. Normally a factory pcv would be located on one valve cover and the breather on the opposite side so fresh air is pulled down into the crankcase back out the opposite valve cover flushing out all of the blowby gases to prevent the oil from getting contaminated which creates an acid. The breather would have a hose going to the inside of the air filter housing where the air has already passed through the filter. There are times when the pcv cannot handle all of the blowby., then it goes out the breather and into the air cleaner housing where the engine burns it. This prevents it from escaping into the atmosphere and creating smog. If you suspect air leaks in the crankcase, I've never tried it but You could put a hair dryer on the fill tube and check around the engine for air coming out. We had a smoke machine at work that used heated mineral oil for testing evap systems on vehicles with charcoal canisters. If you have ever had a car fail the evap test and it wasn't the usual bad gas gap that is how you find the leak. You fill the entire gas tank and evap system with smoke and see where it comes out, it stinks the hole shop up. There is a good chance on an old engine it is tired and then I wouldn't worry about it and just drive it. PCV valve on a worn engine is going to suck up the excess blowby along with oil and it will coat the valves which will turn to a hard carbon until there is so much of it on the valves the air can barely flow past it. You can do a compression check on the engine and then repeat it with a couple squirts of oil in each cylinder. If the compression comes up the rings are worn. I have early cars with no pcv valves, and I don't drive them that much. I just change the oil when it gets slightly dirty. If you are building a new engine and want to install a pcv valve you can otherwise I wouldn't worry about it on an old engine.