Another rear main leak

Jonas A

Jonas A

Junior Member
Hi!

Im new to Ford Model A and have had much help from you guys (and girls), whatever I have searched for I have most of the times ended up reading on this forum! Thanks!

Now Im in need of your advice since im struggling to sort out my (cars) rear main leak....

I have probably read most of the threads on rear main leak on this forum but im still not sure whats causing it.

Some of whats not causing it:
No leak between engine and flywheel housing.
No leak between rear main cap and block.
Crank case breather isnt restricted.
No excessive crank case pressure.
Rear main oil tube (3/8") isnt restricted and is correct length.
No cracks or chips in babbitt.
Crank end play is 0.002"

I have a steady "flow" of oil out the back of the rear main. It starts dripping
~1 minute after staring the engine.
Don´t know how to post a movie, but its about one drip/second when engine is warm.

My thoughts...

Rear main has .002 clearance, could this cause a leak this bad?

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Babbitt looks ok but only has one oil groove, not two in a cross like I have seen in pictures. Could this cause the leak of should one groove be enough?

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Thrust face isnt very wide (and I think it should be wider?), can this be the cause for leak?

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Oil slinger has been removed from crank and a "modern" seal has been fitted. It doesnt fit very tight to the crank and it showing signs of deterioration. With the rear main cap removed it can be turned on the crank.
Is it meant to turn with the crank?
Could this alone cause the leak?

picture.php



Any thoughts/help are appreciated!

Regards
Jonas
 
From my experience those "modern" seals are hit and miss, mainly miss. Getting one fitted so that it works is NOT easy. I bet that is why you have the leak.
Your bearing looks good but I agree the thrust face could be better. I don't think that is causing the leak though.
 
The seal should not rotate with the crankshaft. Some years ago, Goodyear sent EPDM rubber instead of Nitrile and some seals were molded using the wrong material.

EPDM swells when exposed to motor oil. so if the seal lips are not tight on the crankshaft rubbing surface, either the rubbing surface is smaller than 2.090 inches in diameter or the seal is the wrong material.

If the crankshaft is OK, send me your address and reply to model.a.engine@hotmail.com and I'll send a new seal.
 
So you think changing the seal will sort my leak and bearing clearance, oil grove in babbitt and thrust (hopefully the thrust in the upper half looks better) can be left as is?


I will change the aluminum insert (A-6335) at the same time. Anything else that I should change in this area when I have the engine out?

Thanks Terry but Ill be ordering some other parts at the same time (adjustable tappets etc..).
Are there still "bad" seals out there that should be avoided?
 
Seen it, been there …
Your end play is too much. Max. 0.0015, better 0.0010. Oil leaves from behind rather than being forced through the little pipe. Solder babbitt on the front face of the lower bearing cap.
Oil grooves should never have been there anyway.
Your thrust is not OK.
 
Terry Burtz said:
The seal should not rotate with the crankshaft. Some years ago, Goodyear sent EPDM rubber instead of Nitrile and some seals were molded using the wrong material.

EPDM swells when exposed to motor oil. so if the seal lips are not tight on the crankshaft rubbing surface, either the rubbing surface is smaller than 2.090 inches in diameter or the seal is the wrong material.

If the crankshaft is OK, send me your address and reply to model.a.engine@hotmail.com and I'll send a new seal.
Click to expand...
That was indeed very kind of you Terry!
Wayne
 
Jonas A said:
So you think changing the seal will sort my leak and bearing clearance, oil grove in babbitt and thrust (hopefully the thrust in the upper half looks better) can be left as is?


I will change the aluminum insert (A-6335) at the same time. Anything else that I should change in this area when I have the engine out?

Thanks Terry but Ill be ordering some other parts at the same time (adjustable tappets etc..).
Are there still "bad" seals out there that should be avoided?
Click to expand...



Jonas,

A new seal won't solve any bearing issues.

The rear main seal installation instructions are pasted below.

1)Thoroughly clean the grooves in the rear main bearing cap (A-6327) and block insert (A-6335) to remove all traces of dirt and oil, which may interfere with proper seal installation and sealant adhesion. Also, make sure the rear main cap drain pipe is clear.

2)Without the crankshaft in place, assemble the seal with its lip facing towards the front of the engine, shims, block insert, and rear main cap to the engine. Check to be sure the seal fits properly in its grooves, and is not distorted or offset relative to the rear main bearing. The seal is designed to fit snugly into the original block insert (A-6335). Most reproduction block inserts have a groove that is not compatible with this seal.

3)Machine the rear slinger area of the crankshaft as shown in the figure. The finished diameter shall be between 2.090 in. and 2.150 in., and concentric with the rear main journal within .001 in. to prevent whipping of the seal lip outward. Machine crankshaft to the largest diameter between limits consistent with the cleanup. Polish the seal contact area of the crankshaft to a bright smooth finish. Main bearing clearance must be between .0010 in. and .0015 in. to keep the crankshaft from whipping the seal lip outward.

4)Deburr the flywheel mounting flange. Apply some grease to the seal contact area. Carefully and without stretching it more than necessary, lubricate and slip the seal with the lip facing towards the front of the engine over the flywheel mounting flange. A plastic sandwich bag placed over the flywheel mounting flange will protect the seal lip from damage due to small burrs, and a small blunt screwdriver may be required to ease the seal over the flange.

5)On final assembly, apply either an RTV silicone adhesive or Permatex #2 sparingly to both grooves and all mating surfaces where shims, rear main cap, block insert, and block meet. Avoid getting adhesive on the seal lip. Also, apply a sealant to the rear main bolts.

6)Before installing the oil pan, and after the adhesive has cured, test the seal and rear main cap area for leakage by pressurizing the rear main cap drain pipe with motor oil to at least 10 psi and check for leaks. The seal will withstand 50 psi, however, the sealant may fail at this pressure.

7)On occasion due to a hidden manufacturing defect (one out of 1000 seals), the seal will break while being stretched. If this should happen, return the broken seal for a free replacement.



Please confirm that your crankshaft meets the requirements in the installation instructions.

If your crankshaft is OK, immerse your seal in hot motor oil and see if it expands. If it expands, it is made from EPDM which is not oil resistant and you need a new seal.

Per the instructions, the seal is designed to fit the groove in an original A-6335 insert. I would be hesitant on buying a new A-6335 insert because most of the aftermarket A-6335 inserts have a groove that will distort the seal.

Original A-6335 inserts can be sourced from rebuilders that have lots of engine cores that are not rebuildable and need to be scrapped.

Just yesterday, we finished molding a production run of 500 rear main seals using Nitrile from Goodyear that they have certified to be Nitrile, and tomorrow, I'm sending 100 rear main seals to Snyder's.

The material problem came to my attention about 6 months ago when someone sent a seal that leaked. I placed the seal in hot oil and immediately knew that it was not Nitrile. I notified the Model A parts dealers and advised them of this problem, and from your description, I think that your seal is molded from EPDM.
 
Last edited:
Terry Burtz said:
Jonas,

The rear main seal installation instructions are pasted below.

1)Thoroughly clean the grooves in the rear main bearing cap (A-6327) and block insert (A-6335) to remove all traces of dirt and oil, which may interfere with proper seal installation and sealant adhesion. Also, make sure the rear main cap drain pipe is clear.

2)Without the crankshaft in place, assemble the seal with its lip facing towards the front of the engine, shims, block insert, and rear main cap to the engine. Check to be sure the seal fits properly in its grooves, and is not d.
Click to expand...

Thanks Terry, excellent information!
You know your seals, sending you a email!

/Jonas
 
Got the thrust on the rear main sorted:

picture.php


Also I think the "modern" seal that was on the crank was fitted the wrong way around with the lip facing the rear of the engine!

picture.php
 
JoeCB said:
the lip facing out !!! that will ensure a good flow leak
Joe B
Click to expand...

Yes, not sure what was going through their heads when it was assembled... Maybe to much garage beer, Im just glad they didnt fit the whole crankshaft the wrong way :-)
 
Really the most interesting series of posts and brilliant pictures . I have two 1930 pickups both have way excessive end clearance about 25 thou. but they both have no rear main leak at all . No drips on my driveway in Suffolk County England and none on the street outside my " snowbird" trailer in sunny but chill mornings Chandler AZ . I am a firm believer in the " if it aint broke dont fix it " system !!!. I will pull a motor one day but not yet . I know excessive end float can cause a rear main leak but not every time .

John in sunny morning Chandler AZ ,
 
I thought end play could be up to .008. I had an engine with over .025 that didn't leak but was remove due to a knock on startup after the clutch was depressed.
 
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