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Old 07-14-2020, 08:32 AM   #1
Bob Bidonde
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Default Rear Main Bearing Drain

The OEM drain tube design makes no sense to me. In my opinion, the OEM drain cannot handle the motor oil flow rate from the rear main bearing, so oil backs-up and goes to the ground.

The engine in my 190A has two oil drains. The OEM drain tube is in place although not in the picture. The 2nd oil drain empties into the pan above the oil level. Having driven this engine a few thousand miles, I notice hardly any motor oil leakage, far less than the leakage in my 45B which has the OEM drain only. So I will be removing the OEM oil drain tubes from my engines.
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Old 07-14-2020, 02:20 PM   #2
Kurt in NJ
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Default Re: Rear Main Bearing Drain

What do you consider "hardly any leakage "--- my car is stock, hardly leaks,to me hardly any leakage means it won't leave its mark on your friends new driveway even if pointed uphill some, that the car will wait till the dark of night to drip when nobody's watching
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Old 07-14-2020, 02:38 PM   #3
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Default Re: Rear Main Bearing Drain

If the oil drain tube are not under the oil level won't the crankcase pressure stop the flow of oil draining down? Read the service bulletins with AA trucks oil drain tubes!
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Old 07-14-2020, 07:16 PM   #4
SteveB31
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Default Re: Rear Main Bearing Drain

We build ours stock and they don’t leak. So many people trying to reinvent the wheel. If clarences are right , they won’t leak.
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Old 07-14-2020, 07:20 PM   #5
Bob Bidonde
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Default Re: Rear Main Bearing Drain

Big Hammer, in my experience no, the crankcase pressure has no impact. I am convinced that the occasional drip from my 190A is from the transmission. The drip from my 190A is about 75% less than the drip from my 45B which has the OEM drain tube.
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Old 07-14-2020, 07:32 PM   #6
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Red face Re: Rear Main Bearing Drain

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Originally Posted by SteveB31 View Post
We build ours stock and they donít leak. So many people trying to reinvent the wheel. If clarences are right , they wonít leak.

"...won't leak." Even when you're grinding away in low gear hauling that load of gravel uphill out of the pit?
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Old 07-14-2020, 08:11 PM   #7
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Default Re: Rear Main Bearing Drain

The leakage rate from the rear main bearing is caused by clearance..the drain tube size is relative to the drain back of a properly set bearing.Reduction of crankcase pressure in the valve gallery is real,slight pressure there will pressurize the feed oil to the rear main.My engine has a road draft tube off the top rear of the valve cover,I left it intact when i went through the engine after considering its usefulness some.
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Old 07-14-2020, 08:13 PM   #8
Jack Shaft
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Default Re: Rear Main Bearing Drain

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Originally Posted by 40 Deluxe View Post
"...won't leak." Even when you're grinding away in low gear hauling that load of gravel uphill out of the pit?

they had tipper decks for grain trucks back then,tilt the whole shebang..
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Old 07-14-2020, 08:13 PM   #9
Chuck Sea/Tac
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Default Re: Rear Main Bearing Drain

Mine engine is stock Babbitt and drain and gasket, seals. No leaks to 38,000, no leaks after I adjusted the bearings and put the pan back on2,000 miles ago.
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Old 07-14-2020, 08:14 PM   #10
Chuck Sea/Tac
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Default Re: Rear Main Bearing Drain

I have a couple of the truck drains. They have a check ball.
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Old 07-15-2020, 07:51 AM   #11
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Default Re: Rear Main Bearing Drain

I'll just add. I got my engine back from the rebuilder and shortly after it started leaking. I went longer on the last oil change (was doing every 100 miles for the first 500) and around 300 miles in it stopped leaking... pumped out about half a quart and found it's level. Just like the radiator.
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Old 07-15-2020, 08:15 AM   #12
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Default Re: Rear Main Bearing Drain

I don't know if this is relevant or not but when i bought my car not leaked a LOT from the rear. Not knowing anything about Model A's, I asked here for a possible cause and one of the responses was regarding the drawback tube. I pulled the pan and the tube was missing. In fact, the boss that it screws into was broken (I have since diced that someone must have had the wreck slip while tightening the rear main cap nuts and hit the tube breaking it out of the cap). Anyway, I removed the cap and welded a tube back in place and reset the bearing clearance while i was at it. Took out a couple shims IIRC. While the oil leak didn't "stop" it was GREATLY reduced. Was this from the addition of the tube??, or the bearing clearance adjustment?? or both??. I dunno.
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Old 07-15-2020, 08:36 AM   #13
Jack Shaft
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Default Re: Rear Main Bearing Drain

Ford engineers were pretty sharp,they designed the drain back tube to handle the flow of oil through the rear main bearing with a clearance up to about .0025 or so..exceed the clearance more oil can flow by,'overwhelming the tube diameter and subsequently leaking out the flywheel housing weep hole.

Journal bearings rely on the hydrodynamic principle to support the crankshaft on a cushion of oil.the principle is a constant,.001 per inch of crankshaft diameter,model a crankshaft journal is about 1 1/2 inch diameter? oil clearance .0015. gravity fed or pressurized the principle is constant..

Adding a larger drain capacity doesn't hurt as long as you check your bearings periodically.I prefer an oil spot on the garage floor informing me that my clearances are too wide,Im old,need reminders..
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Old 07-15-2020, 08:39 AM   #14
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Default Re: Rear Main Bearing Drain

Note that the OP's modification is on a B engine which, unlike the Model A, has pressure to the mains. The B engine also has several 1/2 inch holes in the floor of the valve chamber so there isn't a pool of oil to drain down into the rear main after shutdown. Bob's modification appears to leave the rear main cap with a total of three exit ports as compared to the single drain tube in the stock configuration. With the slight pressure in the B engine, this would allow for a greater flow of oil to help cool the bearing, another advantage of this modification.
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Old 07-15-2020, 09:01 AM   #15
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Default Re: Rear Main Bearing Drain

PM sent to zip code 20500.

Last edited by Benson; 07-15-2020 at 12:46 PM.
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Old 07-15-2020, 11:30 AM   #16
Dave in MN
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Default Re: Rear Main Bearing Drain

Quote:
Originally Posted by SteveB31 View Post
We build ours stock and they don’t leak. So many people trying to reinvent the wheel. If clarences are right , they won’t leak.

I agree. From my experience of building almost 200 engines, if clearances and assembly practices are right, they won't leak. Of those almost 200 engines, about 20 of them were "B" engines. I have not had to make these modifications.
That said: If the modification is working for you, that is all that matters. Glad you found a solution for your issue/leak.
Good Day!

Last edited by Dave in MN; 07-15-2020 at 01:23 PM.
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Old 07-16-2020, 11:15 AM   #17
Jim Brierley
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Default Re: Rear Main Bearing Drain

Bob, is that some sort of pre-manufactured tube? It doesn't look home made.
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