Engine block main bearing oil tube replacements.

Sunny the Model A

Sunny the Model A

Senior Member
Alright engine builders, got a good one for you. so I'm doing a complete rebuild on a 31 blockthat has been sitting for about 50 years in the mud. the block is in good shape other than one small bugaboo. the tubes that let oil drain into the main bearings, particularly the rear main are rusted through. i need to replace them to get the motor ready to go to the machine shop to be sleeved, decked and new valve seats installed. has anyone replaced the oiling tubes before? i know they are not exactly in every parts store. they look suspiciously like standard steel tubing but i want to be sure before i start pulling them out
 
I have never done this on a Model A, but on a Model B I have used a section of a push rod, and it worked just fine. I don't remember if I had to enlarge the holes in the lock or not. Hope this helps?
 
I have seen crushed lines, lines cut off, mostly by folks who thought that would be a way to cut down on oil leaking out the rear main? I would use brass thin wall tubing from the hobby store. K&S I believe is the brand. Just find the size that fits inside what is left of the steel tube. Works good, lasts a long time!
 
If you are not pressurizing the mains just about anything will work

I think it would be possible to ream the hole in the valve chamber side a little larger to facilitate pushing the tube into the bearing side
Then take a taper punch or ball bearing to flare the chamber side

I have removed them to pressurize in the past be tapping the bearing end and using a flare fitting with copper tube soldered in

J
 
the rear main oil tube is the biggest mystery, it looks like it was blown open like a pipe bomb. I'm staying 100% stock and just want to replace the tubes. i had the idea of taking a tap, threading the worn tubes and using a small slide hammer to pull them out.
 
Sunny the Model A said:
the rear main oil tube is the biggest mystery, it looks like it was blown open like a pipe bomb. I'm staying 100% stock and just want to replace the tubes. i had the idea of taking a tap, threading the worn tubes and using a small slide hammer to pull them out.
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The tubes are the same material that was originally used in Horn Rods and early center Hood Rods. I have replaced several.

Pipe Bomb .....Likely it was compressed air shot down the tube from the valve galley and the crankshaft clearances were 'plugging' the other end. The sudden blast of high pressure has gotta go somewhere.
 
Definitely plausible theory. i got another engine to pour babbitt in tomorrow but i'll clean up the area on the rear main and take a photo of the tube in question. Looks like i'll be buying some piping to replace it. i presume 3/8 od steel tubing?
 
I need to replace three in my "B" motor.I am not seeing how they would be inserted ? do they go through the main bearing journal before the insert bearing is placed ? What do Brattons call them ?
 
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Bruce of MN said:
Search store for "oil drain tube."
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I am not sure if we are all talking about the same thing.
I thought the OP was referring to the tube (s) in the B motor case , that feed the mains bearings from the oil gallery ,under light pressure .
Not the tube that returns oil to the pan at rear of crank.
 
Sunny the Model A said:
Alright engine builders, got a good one for you. so I'm doing a complete rebuild on a 31 blockthat has been sitting for about 50 years in the mud. the block is in good shape other than one small bugaboo. the tubes that let oil drain into the main bearings, particularly the rear main are rusted through. i need to replace them to get the motor ready to go to the machine shop to be sleeved, decked and new valve seats installed. has anyone replaced the oiling tubes before? i know they are not exactly in every parts store. they look suspiciously like standard steel tubing but i want to be sure before i start pulling them out
Click to expand...

Yes: They can be replaced. They were installed after the block was cast.
Steel tubing.
www.jandm-machine.com
 
Alrighty y'all, got a photo taken, sorry about the wait but i had an engine to babbitt and line bore first. but here is the oil tube on the rear main that feeds it. i have no idea how it happened but for the record the motor still had the crank in it and all the internals when i got it.
 

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Thats odd, almost looks like something got between the crank and the tube during it's rotation and cut or wore the tube away.
 
It's a mystery to be sure, the crank doesn't appear to have any scars from something striking it but i'll double check. one thing concerning is the fact the rods have different size nuts on them and half of them had no cotter keys. the threads are good but maybe something worked loose and detonated the line.
 
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