Machine rear main seal info?

[precisionengine2]

Want to know what is required to machine the rear seal to eliminate oil leaks.

[Tom Wesenberg]

Fix the cause of the leak, which isn't the rear oil slinger. Usually it's a plugged drain pipe on the rear main cap, or too much clearance, etc. on the rear main. The correct fix is easier than removing the crank and machining away the oil slinger to install a different seal.

My rear main doesn't leak a drop and it's a well used engine that I installed as a temporary while I rebuild the original.

[Purdy Swoft]

I agree with Tom. The leak CAN be stopped without removing the rear oil slinger. Usually the drain tube on the rear main or the passage inside the rear main cap will be partially blocked. I have a september 29 strip down that I have owned for 50 years that still has the original babbit and after carefull cleaning and fitting doesn't leak a DROP. Once the rear main oil slinger is removed it can NEVER be replaced. I f the person that removes the slinger makes the slightest mistake, the crankshaft is ruined.

[George Miller]

Those one piece seals that are used when the slinger is machined off, also are prone to leak. I to say fix the real problem.

[Mike V. Florida]

Originally Posted by George Miller

Those one piece seals that are used when the slinger is machined off, also are prone to leak. I to say fix the real problem.

The engine I have now has the "improved" real seal and it leaks like crazy.

[precisionengine2]

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The passage on the rear main cap and the drain tube are unblocked.

[Preacher]

In my quest for the best when I started in this hobby, I read and listened to the great 'expert' and machined of the slinger.....trouble was that the 'expert' did not have a clue what was in his own book. Oh if I could only have waited and listened to the real experts. The experts that have the real life experiences (like on Fordbarn) and not just book learnin'

[Purdy Swoft]

precisionengine2 , Sometimes the drain tube is screwed in too far on the rear main cap and obstructs flow. The only real way to know is to remove the 7/16 welch plug in the front of the cap, if the drain tube protrudes into the passage AT ALL this will cause a bad leak. I always make sure that the mating surface of the main cap is perfectly level. I tape a sheet of sand paper to a flat piece of glass and work the cap back and forth over the flat surface until it is perfectly flat. I use plasti gauge and set the clearance at .002 . After torqueing down the cap I apply a small beat of rtv along the edge where the cap meets the block and smooth it in with my finger. Sometimes the aluminum seal part in the block, if not level with the block on both ends will cause a leak. if the original aluminum part is even with the block, I never remove them. Many times a poor fitting repro aluminum seal will be the problem. Good luck.

[Pete]

On a stock engine, fix it like it was from the factory and it won't leak.

If you have a full pressure engine you need a modern seal..There are several on the market that don't leak IF DONE RIGHT.

[AL in NY]

Precisionengine2: Please read posts under thread "oil leak solved"(yesterday 3:36pm). There's a very good procedure for setting the correct clearance on your main bearings. With the oil drain pipe clean, clearances set correctly and correct crankshaft end play, you should have NO oil leak. Good luck.........

[Larry Brumfield]

Originally Posted by Preacher

In my quest for the best when I started in this hobby, I read and listened to the great 'expert' and machined of the slinger.....trouble was that the 'expert' did not have a clue what was in his own book. Oh if I could only have waited and listened to the real experts. The experts that have the real life experiences (like on Fordbarn) and not just book learnin'

Preacher, who is the great expert?

If it's whom I think it is, he caused me a lot of trouble nearly 20 years ago going around his part of the country and beyond, blowin' his mouth. He told people to run their Brumfield Heads through ovens and then have them resurfaced.

What this "expert" didn't know or care to find out before he blew his mouth was that ALL Brumfield Heads, then and to this day, are heat treated and stress relieved!

The problems experienced by earlier Brumfield Heads had nothing to do with the iron itself.

As a result of some of his minions following his advice, several heads were permanenty ruined by being overheated in various ovens and cooled off in uncontrolled conditions when all they really needed was a simple resurface!

His name is LESS Andrews.


Larry B.

[Preacher]

Nope, not L.A., before him. it doesn't matter now, but I confronted him at a National meet in 2000 KC or 2001 Ohio. didn't want me around while hocking his merchandise....

[Sparky]

Originally Posted by precisionengine2

The passage on the rear main cap and the drain tube are unblocked.

My rear main was leaking quite a bit, but when I had the bearing cap off and put oil into the collector hole, it drained through the tube so I thought the passage was OK. It turned out that the passage in the casting was partially blocked with crud so the oil could not drain fast enough. I removed the plug and ran a drill bit through the passage and that fixed the problem.

[Purdy Swoft]

Sparky, I agree, some will test by blowing compressed air through the drain tube and if a good stream of air comes out the other end, they think that ALL is well, not so. If the threads of the drain tube protrude the least bit into the passageway it will restrict or slow down the flow and cause a bad leak at the rear main. The only way to be sure is to remove the 7/16 welch plug at the front of the cap. I will just add for those that don't have the experience , make sure that you have a replacement before you remove the plug. None of the model A parts vendors that I know of offer this part. Most of the new day counter men that work at the local NAPA or other parts houses have never heard of a welch plug. It took three weeks for me to locate one on the last engine. When I finally lucked out and found one, I bought all that they had, they only had a few and said they never had a call for them.

[Ron/IA]

Purdy - You lost me with the "welch plug". But, it doesn't take much for me to get lost.

I looked up "welch" in Dictionary.com and it came up as a last name or refered to it as someone who welches on a bet.

Can you explain further?

Thanks,

[Larry Brumfield]

Originally Posted by Purdy Swoft

Sparky, I agree, some will test by blowing compressed air through the drain tube and if a good stream of air comes out the other end, they think that ALL is well, not so. If the threads of the drain tube protrude the least bit into the passageway it will restrict or slow down the flow and cause a bad leak at the rear main. The only way to be sure is to remove the 7/16 welch plug at the front of the cap. I will just add for those that don't have the experience , make sure that you have a replacement before you remove the plug. None of the model A parts vendors that I know of offer this part. Most of the new day counter men that work at the local NAPA or other parts houses have never heard of a welch plug. It took three weeks for me to locate one on the last engine. When I finally lucked out and found one, I bought all that they had, they only had a few and said they never had a call for them.

Why remove the plug to check for a protrusion?

For me it's easier to remove the pipe.

Mark the side of the pipe at the base, remove the pipe and then measure the distance from the mark on the side to the end. Sight down the hole in the bearing cap and compare the distance measured on the pipe to the distance available in the hole before protrusion. Make any adjustment necessary, install the pipe and apply a small weld at the base so it can't move.


Larry B.

[Sparky]

Originally Posted by Ron/IA

Purdy - You lost me with the "welch plug". But, it doesn't take much for me to get lost.

I looked up "welch" in Dictionary.com and it came up as a last name or refered to it as someone who welches on a bet.

Can you explain further?

Thanks,

More commonly called a freeze plug or gallery plug. I've never heard of "welch plug" either.

[Sparky]

Originally Posted by Purdy Swoft

Sparky, I agree, some will test by blowing compressed air through the drain tube and if a good stream of air comes out the other end, they think that ALL is well, not so. If the threads of the drain tube protrude the least bit into the passageway it will restrict or slow down the flow and cause a bad leak at the rear main. The only way to be sure is to remove the 7/16 welch plug at the front of the cap. I will just add for those that don't have the experience , make sure that you have a replacement before you remove the plug. None of the model A parts vendors that I know of offer this part. Most of the new day counter men that work at the local NAPA or other parts houses have never heard of a welch plug. It took three weeks for me to locate one on the last engine. When I finally lucked out and found one, I bought all that they had, they only had a few and said they never had a call for them.

I found a common replacement size at NAPA. It was not the original dimension but it worked. When I get home I can check the size.

[Dave in MN]

These galley, welch or passage plugs are re-usable. Remove the drain pipe and drive the welch plug out by placing a small punch through the threaded oil pipe hole against the backside of the plug. One or two sharp raps on the punch with a light hammer is all it takes to remove the plug. Place a rag in front of the plug to trap it as it comes loose. If it flies across the room and is lost they are hard to come by. If the fit is loose when re-installing the same plug, place the plug on your anvil and give it a couple light hits with a large hammer and try it again, this process will straighten and enlarge the plug slightly. Works every time!
The reason I remove every one of these plugs is to pass a drill bit through the oil passage to remove the accumilated babbit, timing gear debris, and sludge. When inserting the drill bit, be carefull when the bit approaches the far end of the passage. The drill bit can wedge into the oil groves in the cap and cause a bit of damage. I use a small cordless driver/drill with a torque setting and hold the rear cap in a gloved hand. Carefull here as a strong drill can peel the cap out of your hand if the bit binds...trust me on this one! Replace the drain pipe..checking that you are not damming the flow with a deeply inserted pipe. I use a die grinder with a 1/4" carbide burr to cut out any of the obstructing pipe while it is in the cap through the welch plug opening. I place a small bit of weld between the pipe and the cap on two sides away from the area for the cork gasket.
Good Day!
Dave in MN

[Larry Brumfield]

Originally Posted by Dave in MN

Place a small bit of weld between the pipe and the cap. Start your weld on the cap and finish on the pipe if using a MIG. The pipe is pretty thin and may melt through if the weld is started on the pipe.
Good Day!
Dave in MN

I look at it differently. I weld from the pipe to the cap. The weld gets hotter the farther it goes. I never melt through the pipe.

Larry B.