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#1 |
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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
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#2 |
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Tube is threaded but usually "spot welded" to prevent it backing out and ending up in the bottom of your oil pan.
Joe K
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#3 |
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Thanks, John
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#4 |
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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 . Last edited by hardtimes; 02-11-2015 at 03:58 PM. Reason: .......... |
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#5 |
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thanks, John
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#6 |
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#7 |
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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
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#8 |
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I forgot to say I took the ball bearing out and replaced the tube. Ed
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#9 |
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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
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#10 | |
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![]() Quote:
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 |
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#11 |
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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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#12 | |
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#13 |
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2 1/2" sounds a little short..........isn't it? I'll have to see if I have a spare original tube to measure.
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#14 |
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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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#15 | |
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You mean yours does not have a bend and the entire pipe is made of brass? |
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#17 |
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#18 |
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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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#19 |
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How does the drain tube work? Considering there must be flow, then why is the bottom end of the drain tube submerged in crankcase oil? I am thinking that the oil drain pipe is not necessary. Here's my theory.
For flow to occur in the drain pipe, the squeeze-out oil pressure developed in the rear main bearing must be sufficient to force oil through the drain pipe and to displace the crankcase oil in the submerged end of the pipe. Why submerge the bottom of the drain pipe? Crankcase atmospheric pressure from the motion of the pistons plus blow-by will act on the oil in the drain pipe whether or not the pipe is submerged. By submerging the end of the drain pipe, flow in the pipe is impeded. Oil flow out of the rear main bearing will find the pathways of least resistance, so will oil spill into the flywheel housing if and or when the drain pipe backs-up? I think yes it does. If the drain pipe is removed from the bearing cap, will oil drain into the crankcase? I say yes it will, perhaps more so, and less oil will leak into the flywheel housing.
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#20 |
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Bob,
Most of the time the crankcase is under positive pressure from any bit of blow-by that is present. If you subject the oil trying to flow from the rear main to any amount of back-pressure, you are going to slow its flow. The oil tube sealed to the rear cap and submerged in the oil in the pan stops this pressure from slowing the flow. The pipe also creates a bit of "draw" on the rear main cap as the pipe is vertical and the oil entering the top of the pipe falls/flows to the level of the oil in the pan. I have fixed more than a few rear main leaks by installing or replacing a missing, short or extremely loose drain tube. Good Day! |
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