Model A oil leak
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nkaminar
Well-known member
There is no real seal at the rear bearing but only a labyrinth. If the pressure is building up in the crankcase it will force oil out the rear bearing. Check that there is no restriction in the cap or if the cap is closing off the breather tube.
The Model B engine had a larger breather tube that does a better job of keeping the oil in the engine and not spitting out at the cap. If you have a Model A breather tube that may be part of the problem. The Model A breather tube is the same diameter as the hole but the Model B breather tube is larger than the hole by a fair amount.
By the way, welcome to the Barn and the Model A hobby.
The Model B engine had a larger breather tube that does a better job of keeping the oil in the engine and not spitting out at the cap. If you have a Model A breather tube that may be part of the problem. The Model A breather tube is the same diameter as the hole but the Model B breather tube is larger than the hole by a fair amount.
By the way, welcome to the Barn and the Model A hobby.
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Marshall V. Daut
Well-known member
From where does it leak? If from the rear main bearing area, a plugged oil filler cap will create pressure inside the crankcase and force oil past the rear main bearing "seal" (it isn't really a seal, only a slinger) If the oil is coming from there, it will not stop dripping immediately after the oil cap is removed, as it reads in your message. Already-leaked oil will continue to run out of the flywheel housing hole at the bottom until the supply has all passed through. That will take a while.
Blow out the oil cap's innards with compressed air to clear it and make sure no one has put a scouring pad or gym sock down the filler pipe. That will definitely create internal pressure and cause all kinds of oil leaks.
Marshall
Blow out the oil cap's innards with compressed air to clear it and make sure no one has put a scouring pad or gym sock down the filler pipe. That will definitely create internal pressure and cause all kinds of oil leaks.
Marshall
Marshall V. Daut
Well-known member
Ha! nkaminar types and posts faster than I do!
M.
M.
Marshall V. Daut
Well-known member
If it still has the Model B filler neck, the cap will be almost twice as big as a Model A's cap.
Marshall
Marshall
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Kurt in NJ
Well-known member
There is a bulletin about the oil fill cap and leaks resulting from it being forced on too far bending the stop tangs and closing off the vent path.
And sometimes people stuff a metal pot scrubbing pad up inside the cap blocking off the ventilation aspect of he oil fill cap.
And sometimes people stuff a metal pot scrubbing pad up inside the cap blocking off the ventilation aspect of he oil fill cap.
Joe K
Well-known member
A rear main leak can be aggravated by maintaining too high an oil level in the pan.
The pan principle of the Model A differs from modern cars. In a Model A the sump exists as a sump - and the oil pump pumps oil "up" to the dipper tray above the oil pan (also the valve guide chamber above that which feeds main bearings.)
That's it. The pump fills the dipper tray and the dippers move oil to the crank bearings and gravity fills the mains.
If you have ANY oil in the sump and the pump inlet is covered (i.e. as little as a half a inch in the sump) your engine is oiled (lubricated) as well as it can be.
True - with less volume of oil, what oil there is will get dirtier "quicker" and instead of a 500 mile oil change (recommended Ford era number) you might have to maintain a 100 mile oil change - lest you plug the few passages where oil can go with sludgy oil.
Most people THINK the oil has to be up to the line on the dip-stick. MODERN thinking. But not so. You can run the oil an inch or so lower, possibly even more than that to make the tendency to drop oil out the rear main even less.
If your Model A is using a spin on filter modification (commonly done) you'll have to examine your particular engine which may be set up to be closer to a modern engine.
Joe K
The pan principle of the Model A differs from modern cars. In a Model A the sump exists as a sump - and the oil pump pumps oil "up" to the dipper tray above the oil pan (also the valve guide chamber above that which feeds main bearings.)
That's it. The pump fills the dipper tray and the dippers move oil to the crank bearings and gravity fills the mains.
If you have ANY oil in the sump and the pump inlet is covered (i.e. as little as a half a inch in the sump) your engine is oiled (lubricated) as well as it can be.
True - with less volume of oil, what oil there is will get dirtier "quicker" and instead of a 500 mile oil change (recommended Ford era number) you might have to maintain a 100 mile oil change - lest you plug the few passages where oil can go with sludgy oil.
Most people THINK the oil has to be up to the line on the dip-stick. MODERN thinking. But not so. You can run the oil an inch or so lower, possibly even more than that to make the tendency to drop oil out the rear main even less.
If your Model A is using a spin on filter modification (commonly done) you'll have to examine your particular engine which may be set up to be closer to a modern engine.
Joe K
Joe K
Well-known member
This true. The B has a "large" valve chamber cover which includes an extra "gallery" to channel to each drop to the mains.
Still - cover the pump inlet (1/2" oil in the sump) and you have all the oil (of questionable quality) you'll ever be able to get.
Joe K
Bob Bidonde
Well-known member
I run Model B engines in both of my Model A's. Here are some causes of excessive rear main bearing leakage:
Excessive bearing clearance;
Damaged babbitt;
Clogged / restricted breather tube;
Excessive oil in the engine.
Leakage may also be from the transmission main shaft bearing.
The Models A & B engines have an inherently poor oil return / drainage system form the rear main bearing, so some oil leakage is normal. The Model B has a pressurized oil feed system to the main bearings, but the hydrodynamic pressure developed in the bearings is thousands of PSI higher. So the pressurization due the oil pump is not a cause of oil leakage.
Excessive bearing clearance;
Damaged babbitt;
Clogged / restricted breather tube;
Excessive oil in the engine.
Leakage may also be from the transmission main shaft bearing.
The Models A & B engines have an inherently poor oil return / drainage system form the rear main bearing, so some oil leakage is normal. The Model B has a pressurized oil feed system to the main bearings, but the hydrodynamic pressure developed in the bearings is thousands of PSI higher. So the pressurization due the oil pump is not a cause of oil leakage.
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Post photo of breather tube and cap.
Also include photo of INSIDE of cap (many people jam all sorts of things inside the caps over the years which causes rear main leaks).
There are many different caps from other engines that fit but MAY restrict air flow.
There was a guy 10 years ago who had a clogged breather cap on a used engine that drained all of oil out in about 70 miles. Engine locked up.
He spent $5000 on a new rebuilt engine.
He removed the clogged cap from used engine and put it on new engine, Filled it with oil and drove off on a long trip.
Seventy miles later the new engine locked up .... the oil pan was completely empty on that one also!
Breather cap (which had a green colored "Chore Boy" pot cleaner jammed inside breather cap) was found to be nearly totally plugged up.
NOTE: If any car is driven short distances and never warmed up in cold weather, a white foam collects in oil pan. When the white foam dries it turns solid inside breather tube CAP and eventually will totally plug up the Chore Boy Pot Scrubber.
Like Marshall says in post 17 they could have also stuffed a ChoreBoy into the breather tube also.
Also include photo of INSIDE of cap (many people jam all sorts of things inside the caps over the years which causes rear main leaks).
There are many different caps from other engines that fit but MAY restrict air flow.
There was a guy 10 years ago who had a clogged breather cap on a used engine that drained all of oil out in about 70 miles. Engine locked up.
He spent $5000 on a new rebuilt engine.
He removed the clogged cap from used engine and put it on new engine, Filled it with oil and drove off on a long trip.
Seventy miles later the new engine locked up .... the oil pan was completely empty on that one also!
Breather cap (which had a green colored "Chore Boy" pot cleaner jammed inside breather cap) was found to be nearly totally plugged up.
NOTE: If any car is driven short distances and never warmed up in cold weather, a white foam collects in oil pan. When the white foam dries it turns solid inside breather tube CAP and eventually will totally plug up the Chore Boy Pot Scrubber.
Like Marshall says in post 17 they could have also stuffed a ChoreBoy into the breather tube also.
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ModelA29
Well-known member
Still not there........ If it leaks with the cap on but not when it's off the problem is the cap. Now ask the question why is it getting too much pressure in the crankcase? Excessive blow by?
Marshall V. Daut
Well-known member
There was a LOT of bad information printed in the "Restorer" during the 1970's when a second wave of owners took over from the original 1950's-1960's MAFCA people, who generally were well-versed in Model A's. This "advice" was coming from people who had been into Model A's for two minutes and then considered themselves "experts" qualified to dispense advice. Gullible people followed their suggestions for "improving" their Model A's. One local guy followed almost every one of those brainstorm recommendations religiously. His Model A became the most unsafe and unreliable Model A in this area because of that. It took me WEEKS to undo the damage and straighten his car out. There was a BIG pile of removed "upgrades" on the garage floor afterwards. He couldn't believe how much better his Model A was mechanically with all those stupid ideas removed.
One of these brilliant ideas was to put a kitchen scouring pad down the oil filler tube or inside the filler cap to reduce blow-by. Rather than finding out WHY there was so much blow-by and repairing that, they reached for the easy to do, simple and quick cure - which almost never works. The "Restorer" printed this Einstein advice almost every year, submitted by someone who thought he had discovered the cure for engine blow-by. Lord knows how many engines were ruined by this advice. 'Kind of like putting a Band-Aid over an open cancer sore. It may conceal the problem, but it doesn't cure it. Every once in a while I thumb through back issues from that period and get a kick out of the stupid suggestions from readers that unaccountably made it into print. That means, it became gospel in the Model A community and has been almost impossible to get rid of. I still see scouring pads and gym socks stuffed in oil filler pipes in cars that a local special interest car shop buys at auctions. To no one's surprise, these are usually rolling death traps mechanically - but have every chrome accessory sold by the vendors. Invariably.
As I suggested earlier, I suspect a scouring pad or something similar had been placed in the filler neck or cap by a previous owner, thus increasing crankcase back pressure. Where's that pressure going to force oil to exit? Yup - through the rear main bearing. That removing the cap stops the leak almost certainly points to the cap itself being the culprit. A cheap fix.
Marshall
One of these brilliant ideas was to put a kitchen scouring pad down the oil filler tube or inside the filler cap to reduce blow-by. Rather than finding out WHY there was so much blow-by and repairing that, they reached for the easy to do, simple and quick cure - which almost never works. The "Restorer" printed this Einstein advice almost every year, submitted by someone who thought he had discovered the cure for engine blow-by. Lord knows how many engines were ruined by this advice. 'Kind of like putting a Band-Aid over an open cancer sore. It may conceal the problem, but it doesn't cure it. Every once in a while I thumb through back issues from that period and get a kick out of the stupid suggestions from readers that unaccountably made it into print. That means, it became gospel in the Model A community and has been almost impossible to get rid of. I still see scouring pads and gym socks stuffed in oil filler pipes in cars that a local special interest car shop buys at auctions. To no one's surprise, these are usually rolling death traps mechanically - but have every chrome accessory sold by the vendors. Invariably.
As I suggested earlier, I suspect a scouring pad or something similar had been placed in the filler neck or cap by a previous owner, thus increasing crankcase back pressure. Where's that pressure going to force oil to exit? Yup - through the rear main bearing. That removing the cap stops the leak almost certainly points to the cap itself being the culprit. A cheap fix.
Marshall
Richard Knight
Senior Member
FYI, for the O.P. all engines have blowby. How much depends on the condition of the engine. How it is dealt with depends on the era of the engine. Breather pipes, road draft tubes, and PCV systems have evolved over the last 100 years. Any blockage or added restriction in the filler pipe or cap is guaranteed to cause additional oil leakage.