Oil drain tube

29spcoupe

29spcoupe

Well-known member
I have a pretty good leak at the back of my engine. I read something about the possibility of the drain tube on the rear main may be plugged. I see in Les Andrews' book that the drain tube is threaded. Can this drain tube be unscrewed without dropping the main bearing cap? John
 
Tube is threaded but usually "spot welded" to prevent it backing out and ending up in the bottom of your oil pan.

Joe K
 
29spcoupe said:
Thanks, John
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Yeah, you can unthread it easily. I put blue thread lock on mine. Some ,probably most , do not use anything. Even if a spot of 'weld' is present, you can remove it and then unscrew it.
BTW...stick something up thru tube after unscrewing it...to ensure that it is clean. Mine would let air pass thru, but was still about half crudded closed.

caveat: the tube/pipe threads are very fine and prone to being cross threaded. Use patience/caution to thread back into cap .
 
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The drain tube can be screwed into the rear main bearing cap too deeply which will impede the oil flow out of the bearing. This will surely cause excessive leakage of oil through the flywheel housing and onto the ground.
 
Several years ago I also had a bad leak at the back of the engine. I removed the oil pan and looked at that tube and found that the previous owner had squeezed the tube and dropped a ball bearing down the tube to restrict the oil flow. I removed the tube and no more leaks. Ed
 
That ball bearing'ed tube may have been a factory install on an engine headed for AA truck use.

The Service Bulletins describe the one-way drain tube variant for "trucks in service where the angle of incline is found regularly greater than 15 degrees" or some such descriptive.

Sort of the reverse of the cotter pin in the flywheel housing IMHO. I expect a LOT of these were removed/retro'ed after getting plugged up on the ball.

Joe K
 
I dropped the pan today and inspected the oil drain tube. The engine appears to have been rebuilt. The drain tube looks like a replacement type (pipe nipple about 2 1/2 inches long). It was in so tight that I had to remove it with vise grips. I am hoping that Bob Bionde is correct about it being in too much. I was able to blow air through the opening, and it appears to be clear. There is absolutely no sludge in the engine or valve galley. Once I get the pan and oil pump back on, I will let you know if the problem is corrected. Thanks to all. John
 
29spcoupe said:
I dropped the pan today and inspected the oil drain tube. The engine appears to have been rebuilt. The drain tube looks like a replacement type (pipe nipple about 2 1/2 inches long). It was in so tight that I had to remove it with vise grips. I am hoping that Bob Bionde is correct about it being in too much. I was able to blow air through the opening, and it appears to be clear. There is absolutely no sludge in the engine or valve galley. Once I get the pan and oil pump back on, I will let you know if the problem is corrected. Thanks to all. John
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I haven't measured one in years but make sure that yours is long enough so that the end of it stays submerged in the oil at all times, even if the oil should happen to get a little low. I have seen them before where the pipes would get broken off by people when doing overhauls, etc. and they would cut the pipe shorter and rethread the end and screw it back in the hole. Everything would be fine until the oil got lower and then the end of the pipe would get exposed to the crankcase pressure and it would travel up the tube and push oil out the back. And of course if a repo pipe or an original was too short the effect would be the same with the oil at full.
 
Mine is definitely a brass pipe nipple. I looked at Snyders' catalog and their tube has a bend in it, but I can't tell the length. I will check with them tomorrow. By looking in the catalog, and comparing the picture with my tube, mine seems to be shorter than the longer part of theirs before the bend. Guess I'll have to call them. John
 
Joe K said:
That ball bearing'ed tube may have been a factory install on an engine headed for AA truck use.

The Service Bulletins describe the one-way drain tube variant for "trucks in service where the angle of incline is found regularly greater than 15 degrees" or some such descriptive.

Sort of the reverse of the cotter pin in the flywheel housing IMHO. I expect a LOT of these were removed/retro'ed after getting plugged up on the ball.

Joe K
Click to expand...

My original Ford Chassis Parts book used at a dealership, dated 1950, lists the same pipe as the replacement for either a car or truck and says "ball check type" and there is no mention of the regular type pipe that we all know. The book says the following:

A-6328-A -- Pipe assy (crankshaft rear bearing oil) - ball check type - 5/16" O.D. 1 required Pass, Comm & Truck (4 cyl) 1928-30

A-6328-B -- Pipe assy (crankshaft rear bearing oil) - ball check type - 3/8" O.D. 1 required Pass, Comm & Truck (4 cyl) 1930-31
 
29spcoupe said:
Mine is definitely a brass pipe nipple. I looked at Snyders' catalog and their tube has a bend in it, but I can't tell the length. I will check with them tomorrow. By looking in the catalog, and comparing the picture with my tube, mine seems to be shorter than the longer part of theirs before the bend. Guess I'll have to call them. John
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You mean yours does not have a bend and the entire pipe is made of brass?
 
I ordered he drain tube today. I am assuming he bend is toward the front of the engine so that it sits in the dripper tray. Is this correct? John
 
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