Rear Main Cap Oil Drain Tube

[A-Man]

Earlier, I submitted a post about an oil leak from the rear main on my 1930 Ford Model A Coupe. This is an oil leak that occurs when the engine is running, and also when the engine is off. After researching and looking at posts on FORDBARN, I have begun the task of looking into the cause of the leak.

Aware that the problem could be the result of a plugged oil drain tube, oil drain tube falling out of the rear main, and/or plugged oil channels in the rear main, I have removed the oil pan. I have also removed the drain pipe which was in place. The drain pipe was NOT clogged. However, the drain pipe looks like it is a homemade pipe, made from copper tubing.

I am including a attachment showing said oil drain tube, along with a picture of a new oil drain tube. Two(2) distinct differences are noted: 1) the length of the OLD tube is around 4-1/2" long, whereas the NEW tube is around 4" long [if I understand, 4" is the correct length] and 2] the number/length of threads is longer, which would allow the tubing to be screwed in farther, and potentially blocking off oil from running through the oil channels in the rear main cap.

My question - could the extra length of the OLD oil tube cause any possible oil leak from the rear main? Obviously, the tube would be immersed further into the oil in the oil pan.

I am debating my next step. I would like to check the oil channels in the rear main for any possible blockage. As the engine is in the Coupe, and the mains are secured in place, can the oil channels be successfully blown out with compressed air? Or does the rear main cap need to be removed to blow out the oil channels?

Another step I am contemplating is the removal of the rear main cap to check for clearances. However, this is getting out of my comfort zone, to undertake this task.

[James Rogers]

First, use the correct tube. Too long probably won't hurt, to a point. 1/2" is probably ok but, I would use the correct one. The threads DO make a difference and can block the oil return. You probably need to remove the rear cap for 2 reasons. One, with it on the bench, you can tap out the plug in the front of the tube and run a drill bit through the tube to make sure it is clear. Second, you probably need to clearance the bearing. Most leaks at the rear bearing is more often than not a clearance issue. It will also give you a chance to inspect the bearing condition for cracks, improper pouring, or voids. Checking the clearance is not a complicated job and not to be feared. Use the aluminum foil method and you will never fear this again.

[Marshall V. Daut]

As a follow up to James' advice, don't stop at adjusting the rear main. The center main is just as important, if not more so. A loose center main causes the crankshaft to "whip" with the center main acting as a fulcrum. This whipping allows oil to escape through the rear main bearing. Adjusting the rear main without also adjusting the center main will gain very little. It's a hassle to remove the manifolds and valve cover to do this, that is true; but you've already got the oil pan off and you're going to get oily anyway doing the rear main. Do the job properly and you might be able to stop (temporarily) or at least drastically reduce oil leakage in this area.
The front main bearing usually doesn't need much adjusting, if any. Check it anyway. Either remove or swing the generator out of the way and go for that one, too, since you're there anyway. Make a day of it for peace of mind!
By the way, it's usually the center main's Babbitt that fails first because of the whipping action I have described. The Babbitt gets pounded and eventually cracks, causing the dreaded heavy pounding sound we've all heard deep within the engine. If guys kept the center bearing's adjustment within acceptable tolerances, many of the dramatic center main failures would not occur. That poor center main takes more abuse than the rear main, even with the heavy flywheel weighing down on it. The rear main bearing offers a greater surface area to handle the extra weight, which is why when it fails, it isn't usually as catastrophic as a rear main failure, assuming the Babbitt job was done properly.
Marshall

[Will N]

You really do need to check the rear main clearance, and also the fore/aft thrust movement. Too much clearance and to much end play will result in more oil pumping past the rear main than the slinger and return tube can handle.

[Bob Bidonde]

Do you notice anything different about this Model "B" engine? Look carefully at the rear main bearing cap. It has three oil drains in the bearing cap, but the stock drain tube is not in yet. I use 100% synthetic 10W30 motor oil for its superior squeeze-out resistance.

This completely rebuilt engine has about 500 miles on it. I have run it at 60 plus mph sustained for 15 miles without any noticeable leakage from the rear main bearing.

The negative of this rear main bearing modification is the notch that was cut into the flywheel housing to clear the second oil return manifold. I do not recommend this modification because the notch reduces the fatigue life of the housing.

[James Rogers]

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Originally Posted by Bob Bidonde

Do you notice anything different about this Model "B" engine? Look carefully at the rear main bearing cap. It has three oil drains in the bearing cap, but the stock drain tube is not in yet. I use 100% synthetic 10W30 motor oil for its superior squeeze-out resistance.

This completely rebuilt engine has about 500 miles on it. I have run it at 60 plus mph sustained for 15 miles without any noticeable leakage from the rear main bearing.

The negative of this rear main bearing modification is the notch that was cut into the flywheel housing to clear the second oil return manifold. I do not recommend this modification because the notch reduces the fatigue life of the housing.

If the rear babbitt was done correctly, it wouldn't need all that mess.

[A-Man]

Thanks, James, for your response. I most definitely will be using the NEW CORRECT pipe. And will be removing the rear cap, as you suggested. However, you got me stumped - what is "Use the aluminum foil method and you will never fear this again."?

Thanks, too, to Marshall and Will for their comments.

[James Rogers]

I check the clearance with a 2"X1" piece of heavy duty aluminum foil folded in half tom make a 1"X1" square. Place the foil in the cap and replace it and tighten it securely as close to the torque as possible. Try to turn the engine with the crank handle while laying under the car. If it turns easily, remove the cap and peel a shim off one side or the other and replace the cap and try it again. Keep trying this by removing shims from alternating sides till significant resistance is felt when turning the crank handle. At this point, remove the cap, remove the foil and replace the cap and torque. This method can be used on any of the rod or main bearings and is the one sure way of getting the rear correct with the weight of the flywheel on it and negates the use of a jack.

[A-Man]

Thanks, James. I guess it is true, you are never too old to learn, and you learn something new everyday!

[denniskliesen]

Would it be a mistake to drill and tap the rear main from 5/16" to 3/8" drain tube? I've read many posts on rear main leaks and what can be the cause. Don't remember reading anything about changing drain tube size.

[Chuck Sea/Tac]

Yes, I've done it, but it's a special tap I had to order. I believe it's 3/8" X 32.

[denniskliesen]

Chuck, did you get a standard or bottoming tap?

[George Miller]

I agree with James and Marshall

[Utopia Texas]

The bearing shims are laminated in a pack so peeling off just one thin layer can sometimes be a PIA. I always keep my reading glasses and single edged razor blade handy to start the peeling at one edge. Save any peeled off shims for a later date. I have used a micrometer on a pile of peeled off shims and they are not always the same thickness and have had to use the mix and match method to get a correct thickness.

[Kohnke Rebabbitting]

Shims for the last few years have a modern glue holding them together, and yes they are a pain in the South side of a man traveling North.

That job is made easy again if you take a snout nose plier, and hold the pack in a small flame, and the glue will burn away, leaving the shim easy to peal.

Always change over to the 3/8's larger pipe.

Don't skip any drill bits from 5/16 to 3/8's, or you will have problems.

[1crosscut]

James when you set clearances with the foil do you oil it or use it dry?

[Kohnke Rebabbitting]

The first thing you should do with the tin foil Dave, is scrap off all the hardened burnt crust, left by the roast beef on the gas grill.

[1crosscut]

Sounds good Herm. Just curious.
When is dinner?

[Dave in MN]

[QUOTE=Kohnke Rebabbitting;1511538]Shims for the last few years have a modern glue holding them together, and yes they are a pain in the South side of a man traveling North.

That job is made easy again if you take a snout nose plier, and hold the pack in a small flame, and the glue will burn away, leaving the shim easy to peal.

Always change over to the 3/8's larger pipe.

Don't skip any drill bits from 5/16 to 3/8's, or you will have problems.[/QUOTE]

It is not said but I think implied that when the oil drain tube is increased from 5/16" to 3/8", the oil passage through the cap should also be increased from 5/16" to 3/8".
To do so, remove the galley plug and with the rear main cap firmly held in a vice or bolted down to a plate, you pass a drill through the galley plug opening starting with a 5/16' drill to clean any obstructions and then increase one size (by 1/64") at a time to open up the passage to 3/8".
If you try to skip a size, the drill tip will bind in the galley plug opening and either break the bit or damage the cap. Be careful as to the depth you drill so as to not drill through the back side of the cap.
Herms advice regarding not trying to skip a size is spot on.
Good Day!

[RawhideKid]

[QUOTE=Dave in MN;1511894]

Originally Posted by Kohnke Rebabbitting

Shims for the last few years have a modern glue holding them together, and yes they are a pain in the South side of a man traveling North.

That job is made easy again if you take a snout nose plier, and hold the pack in a small flame, and the glue will burn away, leaving the shim easy to peal.

Always change over to the 3/8's larger pipe.

Don't skip any drill bits from 5/16 to 3/8's, or you will have problems.[/QUOTE]

It is not said but I think implied that when the oil drain tube is increased from 5/16" to 3/8", the oil passage through the cap should also be increased from 5/16" to 3/8".
To do so, remove the galley plug and with the rear main cap firmly held in a vice or bolted down to a plate, you pass a drill through the galley plug opening starting with a 5/16' drill to clean any obstructions and then increase one size (by 1/16") at a time to open up the passage to 3/8".
If you try to skip a size, the drill tip will bind in the galley plug opening and either break the bit or damage the cap. Be careful as to the depth you drill so as to not drill through the back side of the cap.
Herms advice regarding not trying to skip a size is spot on.
Good Day!

Um, I am a bit puzzled, but from 5/16 to 3/8 is only 1 1/16 drill size.
If you and Herm were referring to the drill size steps by 64ths there will be 5 drills to gain the 3/8 size.

1st. 5/16 to clear obstructions.
2nd. 21/64
3rd. 11/32
4th. 23/64
5th. 3/8

Now, there are more drill sizes between there IF you count the Lettered drills, but I don't think that is what you were referring to. Those would include O, P, Q, R, S, T, and U before you get to the 3/8. So, if you indeed only go a 1/16 step, it only takes 2 drills.

[Dave in MN]

OOPS! I meant by 1/64th...Sorry. I went back and corrected my original post. Thanks for bringing it to my attention!

[QUOTE=RawhideKid;1511904]

Originally Posted by Dave in MN

Um, I am a bit puzzled, but from 5/16 to 3/8 is only 1 1/16 drill size.
If you and Herm were referring to the drill size steps by 64ths there will be 5 drills to gain the 3/8 size.

1st. 5/16 to clear obstructions.
2nd. 21/64
3rd. 11/32
4th. 23/64
5th. 3/8

Now, there are more drill sizes between there IF you count the Lettered drills, but I don't think that is what you were referring to. Those would include O, P, Q, R, S, T, and U before you get to the 3/8. So, if you indeed only go a 1/16 step, it only takes 2 drills.