Curiosity Re Main Bearing Oil Drainage

[Bob Bidonde]

Consider the center & front main bearings in Model "A" & "B" motors. They drain by oil squeeze-out into the oil pan tray. Then why is it that the rear main bearing uses a drain tube? Why not just let the oil squeeze-out into the oil pan?
It's my opinion that the rear main bearing overflows because of poor drainage through the tube.

[old ugly]

the oil pan does not cover the whole bearing.

the oil has to be captured by the rear galleries of the block and bearing cap, once the oil is in the bearing galleries it has to have a route back into the oil pan. the oil flows down the drain hole and down the tube into the oil pan.

that drainage system works quite well as long as it is clear of obstruction, gunk,

[hazelhoff]

Right ! The rear main sticks out into the flywheel housing. We are having trouble enough to keep the oil out of there !

[old ugly]

Originally Posted by hazelhoff

Right ! The rear main sticks out into the flywheel housing. We are having trouble enough to keep the oil out of there !

haha
ford took care of that problem he drilled a hole in the bottom of the bell housing so the oil wouldn't accumulate in there.

[nkaminar]

A little bit of leaking oil lubricates the ball at the end of the wish bone (radius rods). The slinger at the rear of the crankshaft is supposed to sling any oil coming from the rear main into the little catch basin so that it can drain back into the engine pan. If the rear main is throwing too much oil at the slinger it can be overcome causing excessive leakage at the rear of the engine. Or if the little tube is clogged or too short the oil will leak out the rear of the engine.

[Bob Bidonde]

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I think some of the replies miss my point. The middle & front main bearings do not have an oil drain tube, so why is there a drain tube in the rear main bearing? In my opinion, the drain tube has inadequate capacity because its end is submerged in oil. This causes oil to overflow the rear main bearing cap.
If the rear main bearing did not leak, oil leakage from the front transmission bearing would keep the radius rod ball joint lubricated.

[nkaminar]

The front bearing is sealed with the rope seal. The rear could also be sealed in a similar fashion. But the Ford engineers decided to use the slinger, tube design instead. That works OK if everything is right, but can be overwhelmed when there is excessive clearance in the rear main or another problem.

You can get the crankshaft machined to use a modern lip seal at the rear. The Burtz block uses a modern seal there. The modern seal will work OK if the shaft is polished but will eventually wear out and you will have to take the engine apart to replace it. The slinger system has no wearing parts so it will last indefinitely as long as it does not get overwhelmed. All modern engines use a lip seal at the rear main.

The Ford engineers designed the tube to be long enough to extend down into the oil so that excessive pressure in the crankcase would not force the oil up the tube and overwhelm the slinger system.

[old ugly]

the drain tube is necessary on the rear main to redirect the oil back into the oil pan.
the bearings are oiled from gravity. oil comes down the oil gallery from the side chamber. the bearing is oiled across its total surface length which means the escaping oil comes out the front and rear of that bearing.
in the model A the only escape route for the oil at the rear of the bearing is the drain back system in the rear main cap, then down the tube into the pan
if there were no drain back on that bearing the oil would just overflow into the bell housing, lots of oil.

seal technology has change a lot. the model A is average technology for its time and the costs of the car you were buying. and a bit of oil drip was a normal thing.

i have in the past filled an oil pan with 5 qt of oil to see how high the oil level is when its on the engine at the correct angle.
i don't think the oil tube extends into the oil but i am not completely sure of that. especially when folks say they only run 4 quarts in their cars. even if the tube runs into the oil the returning oil will still run freely into the pan.
try it with water. put your funnel into a bucket of water submerge the end of the funnel and start pouring. you will find the water still flows freely into the bucket.

[Dave in MN]

From Bob (Post #1) "In my opinion, the drain tube has inadequate capacity because its end is submerged in oil. This causes oil to overflow the rear main bearing cap."

Bob, you have stated your theory before. (Quote above) I don't agree with your theory that submerging the lower portion of the tube in oil restricts flow to any great extent. I agree with the theory that the oil tube tip is into the pan oil to prevent positive crankcase pressure from interrupting the oil flow from the rear cap causing it to flow out the rear cap.
A blocked engine breather and leaky rings could push lots of oil out the back if the drain tube tip did not reside in the oil.

Stating the obvious: A rear main leak occurs when bearing clearances are excessive and the resulting oil passing through the bearing overwhelms the capacity of the drainage system.

It's my opinion, that if a rear main leak is present, look for restriction to the original drain system and if finding none, correct the issue at the cause and that cause is too much oil passing through the bearing because of excessive clearance. Decrease the clearances.

Installing a new correctly fitted 3/8" (A-6328-B) oil drain if you currently have one of the smaller 5/16" (A-6328-A) oil drains is a good step to improving oil flow. The rear main caps that originally had the 5/16" drain tubes had a smaller passage in the cap. Opening up the oil passage in the rear main cap to 3/8" while doing this conversion is prudent.

When I rebuild engines with insert bearings, if a cap has the small diameter 5/16" drain system, I convert it to the larger 3/8" system. I have learned that not doing so can result in a rear main leak.

Good Day!

[old ugly]

Originally Posted by Bob Bidonde

Consider the center & front main bearings in Model "A" & "B" motors. They drain by oil squeeze-out into the oil pan tray. Then why is it that the rear main bearing uses a drain tube? Why not just let the oil squeeze-out into the oil pan?
It's my opinion that the rear main bearing overflows because of poor drainage through the tube.

in your original post you asked why the main bearing uses a drain tube.
i thought you were looking to know why the rear main uses a drain tube so i answered that.

your opinion is probably correct as far as draining through the tube, and ford did try to address that by increasing the tube size. if every thing is clean and fitted properly it works.
Did he build the car to last 90 years, maybe, but it also needed to be maintained which means fitting and cleaning.

basically we are dealing with a low end, low priced car. made affordable to the public.
MY OPINION is the system that was engineered in 1927 works good for the time frame and the quality of car that was being built.

in our day and age YOU have the option to transform that engine, or the whole car, into whatever you want. if you want inserts, if you want modern seals , if you want a 5 bearing block, these options were not offered by Ford, he offered what people could afford with the engineering available at the time to supply that.
if you want it like a modern car go for it.

[PC/SR]

If you get excessive oil leak, check for excessive crankshaft end play. Too much movement acts like an oil pump to the rear.

[nkaminar]

The Service Bulletins say to keep the crankcase breather clear or the pressure in the crankcase will build up and push oil out the rear main. Maybe the opposite is true. A PCV valve hooked to the intake manifold may reduce the pressure inside the crankcase to the point of stopping a leaking rear main. What do you think?

[old ugly]

Originally Posted by nkaminar

The Service Bulletins say to keep the crankcase breather clear or the pressure in the crankcase will build up and push oil out the rear main. Maybe the opposite is true. A PCV valve hooked to the intake manifold may reduce the pressure inside the crankcase to the point of stopping a leaking rear main. What do you think?

pcc would stop blowby out the filler cap, maybe keep that area cleaner. if a guy had a spare side cover plate and fit the pcc valve in there with a hose to the intake manifold, maybe a good experiment.
you might need an air filter on the filler tube so dirt doesn't get carried into the engine.
has it been done?

[Bruce of MN]

A PCV would require sealing the filler cap to have any effect.

[rotorwrench]

I'm sure that Ford extended the oil tube down into the oil to keep crankcase pressures from pushing pressure up into the slinger annulus which would cause oil to be forced out the rear of the main cap. The pressure in the crankcase can get high enough in extreme wear conditions to keep a constant positive pressure down in that area. It doesn't take much pressure to stop the flow of oil. The other thing that wears besides rings are the main bearings themselves. The more they wear, the more the increased clearance allows more oil to make its way passed the worn bearings.

A Positive crankcase ventilation system has to have a good vacuum source from engine manifold air pressure and a way for air to circulate inside the engine. It would likely draw air back though the oil filler cap so it would require it to have a filter on the cap to insure clean air in there.

[PC/SR]

I ran a PCV valve once but did not like it. Now I use 1/4" NPT 90 degree brass fitting. I drill and tap the threads in the upper rear of the valve cover, Works fine. Adds another pressure release point. No oil drips or splash out. You can actually feel little puffs coming out as the cylinder blow-by happens.

[California Travieso]

Would an oil pump with a higher capacity help this problem by moving the oil out Of the oil pan more quickly? There are suppliers that offer them.

David Serrano

[katy]

Anyone try running an engine w/the drain tube removed?

[old ugly]

Originally Posted by katy

Anyone try running an engine w/the drain tube removed?

i have had engines apart that the tube was not there or it had been shortened but i don't know if the engine was a leaker or if it helped

[1crosscut]

Originally Posted by katy

Anyone try running an engine w/the drain tube removed?

A club member bought an A that left a trail of oil behind it. Pulled the pan and found the oil drain tube was missing. Replaced it and it leaked very little afterwards.