Rear main seal
- Thread starter 31 RPU
- Start date
James Rogers
Well-known member
Albert, only 2 things commonly cause leaking from the rear main if the babbitt is not broken. 1 is the thrust clearance is to great, Ford specified from .003 to .012. 2 the bearing clearance is to great, Ford specified it to be .0015 to .002. This is if the tube is clear and not blocked in any way and is intact.
BTW, I used to use the cork seal and the neoprene seal but, quit because of so many failures. I had about a 10% reliability rate and a 90% fail rate.
BTW, I used to use the cork seal and the neoprene seal but, quit because of so many failures. I had about a 10% reliability rate and a 90% fail rate.
Now I am getting really confused. This started out with 31 RPU asking a question about modern seals, then "olut" has an oil leak, next Terry NJ has a leaking oil issue, now MAG refers to some engine that apparently was fixed without a modern seal, and who is Albert?
How about folks start their own thread with their own questions? Much easier to keep track of and address that way.
How about folks start their own thread with their own questions? Much easier to keep track of and address that way.
olut
Member
Sorry, I thought, it is more polite and useful to stay with the topic and thread rather than starting a new one. I searched for similar topics and found only this one matching my problem/issue, is it smart to switch from generation one of shaft sealing to generation two with Köck/neoprene halts.
Thank you to all of you for your very informative replies, which I am going to forward to my mechanic and the engine rebuilder.
The interesting thing is the fact, that all oil along the rear crank shaft practically has to be slingered off, spraying the oil into the U-profile of the ring and has to ran off quickly. That further means, either there is too much oil comming into this area, which cannot be influenced unless something is broken, or the oil does not ran off fast enough, which could be a matter of blockage inside the tube.
As a mechanical engineer I see the fact, that whatever I will do, a proper seal effect is more likely a matter of good luck than good engineering. The solution with kork/neoprene at least increases the chance of a controlled reduction of oil leaving the engine at this place, if machining is performed correctly and as long pressurizing the engine can be avoided with a functioning oil cap.
In my case, the clearance of the crankshaft is within the tolerances, no cracks, no Babbitt issues, nothing which indicates a common explaination, means, getting rid of the slinger and go for Russian roulette with kork/neoprene will not make my problem worse but gives a chance of some improvement..
Thank you guys for your kind input
Albert
Thank you to all of you for your very informative replies, which I am going to forward to my mechanic and the engine rebuilder.
The interesting thing is the fact, that all oil along the rear crank shaft practically has to be slingered off, spraying the oil into the U-profile of the ring and has to ran off quickly. That further means, either there is too much oil comming into this area, which cannot be influenced unless something is broken, or the oil does not ran off fast enough, which could be a matter of blockage inside the tube.
As a mechanical engineer I see the fact, that whatever I will do, a proper seal effect is more likely a matter of good luck than good engineering. The solution with kork/neoprene at least increases the chance of a controlled reduction of oil leaving the engine at this place, if machining is performed correctly and as long pressurizing the engine can be avoided with a functioning oil cap.
In my case, the clearance of the crankshaft is within the tolerances, no cracks, no Babbitt issues, nothing which indicates a common explaination, means, getting rid of the slinger and go for Russian roulette with kork/neoprene will not make my problem worse but gives a chance of some improvement..
Thank you guys for your kind input
Albert
Kohnke Rebabbitting
Well-known member
Check to see that the crank is centered in the block. The crank should be equal distance from each main bolt.
If it is a larger distance on one side, that means that you have that much more gap from the crank slinger to the Aluminum slinger for oil to go through.
Check the shims to see if they are touching the crank, and the bolts do not keep them from doing that, and the slinger end of the shims touch the crank with no gap.
Olut: Well, the thread has morphed from RPU's question to your oil leak. That said, a properly restored rear main will not leak more than the usual few drops, period, as proven by 80 years of experience.
If yours leaks, something other than the original engineering is wrong. It is not a matter of luck, but an assembly problem. I really doubt there is as you say a mathematically higher chance of success with a modern seal. From an engineering point of view, the Model A does not "seal" the rear main, but collects the excess oil and directs it to the pan through the tube to the pan.
In my experience, the usual problem is the aluminum "seal" is not dead flat with the block. Use a file to check. Your eyeball and finger are not good enough. The "seal" usually protrudes above the block plane a little bit and should protrude a little bit. That allows you to file them down to a correct fit. If, as you suggest, you had a mechanic do the work, well, your trust is in him......up to you.
Sometimes, if not installed evenly, one end is below the plane of the block. Tap the other side to get it above the block plane, then file it down.
There are other reason for leakage. There are numerous threads on rear main leaks in the Search function. Do the checks that Kohnke recommends. Maybe the cam gasket leaks. Maybe the return galley is impaired. Maybe your mechanic is wrong about the oil return passage (they are wrong sometimes) check it yourself. Maybe you have too much blowby creating excess crankcase pressure. Maybe you just have too much oil in the crankcase. Maybe the pan gasket was improperly installed. Maybe the oil grooves are wrong. All these things and more have been identified as causes of leakage.
There is simply no reason to install a modern seal. Get the original right and it will work.
If yours leaks, something other than the original engineering is wrong. It is not a matter of luck, but an assembly problem. I really doubt there is as you say a mathematically higher chance of success with a modern seal. From an engineering point of view, the Model A does not "seal" the rear main, but collects the excess oil and directs it to the pan through the tube to the pan.
In my experience, the usual problem is the aluminum "seal" is not dead flat with the block. Use a file to check. Your eyeball and finger are not good enough. The "seal" usually protrudes above the block plane a little bit and should protrude a little bit. That allows you to file them down to a correct fit. If, as you suggest, you had a mechanic do the work, well, your trust is in him......up to you.
Sometimes, if not installed evenly, one end is below the plane of the block. Tap the other side to get it above the block plane, then file it down.
There are other reason for leakage. There are numerous threads on rear main leaks in the Search function. Do the checks that Kohnke recommends. Maybe the cam gasket leaks. Maybe the return galley is impaired. Maybe your mechanic is wrong about the oil return passage (they are wrong sometimes) check it yourself. Maybe you have too much blowby creating excess crankcase pressure. Maybe you just have too much oil in the crankcase. Maybe the pan gasket was improperly installed. Maybe the oil grooves are wrong. All these things and more have been identified as causes of leakage.
There is simply no reason to install a modern seal. Get the original right and it will work.
Last edited:
George Miller
Well-known member
along with what has been said. on some engines the bolt holes for the flywheel housing around the cam go into the engine.if lock washer are used they will leak oil around the bolts. it looks like the oil is coming from the rear main. I always use a sealer on those bolts.
Kurt in NJ
Well-known member
Another cause of leaks is the surface of the block and cap, sometimes they have been filed with a dirty file making grooves in the surface --I used hylomar on the block, cap and between any loose shims.
Herm mentioned checking that the crank is centered in the block ---that the gap between the slinger and the opposing surface is equal ---I took it a step further, I selected the total thickness of the shim pack to make the clearance equal all around the cap too ---Ford didn't use a thick shim pack, the cap is designed to not have a thick shim pack, if you use a thick shim pack with a cap that hasn't been filed or cut much you will have a much larger gap at the bottom of the cap to the slinger ---
I don't think Ford used more than .005 of shims, if you use a .035 shim pack you could have an xtra .030 in gap beyond the factory design tolerance ---when this opening isn't concentric with the crankshaft as the gap widens oil will be drawn in---as it closes that oil will be pushed out--add in a little loosness, a crankshaft cut slightly off center, some bad filing, poor shim placement, bad glue job, and a partially obstructed drain it's no wonder there are all sorts of "cures" being tried ---until the root causes are fixed the bandaids will have trouble.
Sometimes a rear main babbitt failure can wear away the surface in the cap too.
Proper restoration to original tolerances will eliminate the need for most modifications.
Herm mentioned checking that the crank is centered in the block ---that the gap between the slinger and the opposing surface is equal ---I took it a step further, I selected the total thickness of the shim pack to make the clearance equal all around the cap too ---Ford didn't use a thick shim pack, the cap is designed to not have a thick shim pack, if you use a thick shim pack with a cap that hasn't been filed or cut much you will have a much larger gap at the bottom of the cap to the slinger ---
I don't think Ford used more than .005 of shims, if you use a .035 shim pack you could have an xtra .030 in gap beyond the factory design tolerance ---when this opening isn't concentric with the crankshaft as the gap widens oil will be drawn in---as it closes that oil will be pushed out--add in a little loosness, a crankshaft cut slightly off center, some bad filing, poor shim placement, bad glue job, and a partially obstructed drain it's no wonder there are all sorts of "cures" being tried ---until the root causes are fixed the bandaids will have trouble.
Sometimes a rear main babbitt failure can wear away the surface in the cap too.
Proper restoration to original tolerances will eliminate the need for most modifications.
hardtimes
Well-known member
Hey PC/SR,
I support your position and learned from your input here,thanks
!These guys , IMO, did give some very helpful info and that is appreciated !
However, your 'message' to stay on original poster question ..is spot on and for a couple of good reasons, i.e.- helps the one asking with his/her problem; and encourages others that they can get what they are after and not become discouraged,eh !
That being said, IMO, AFTER you have answered the original poster request to the best of your ability, THEN is appropriate to 'add on'. Just some thots and do not assume any intent from my input.
Can't really tell by looking although as I said earlier it may be that the aluminum seal is protruding, but that may be the light or something. You really have to measure things. If it were me I would pull the crank and start from scratch for a new installation, measuring and checking everything. I would also like to see the oil grooves.
olut
Member
colin1928
Well-known member
Thats great I would be interested to hear how it is going after a couple of thousand miles that seams to be the test
hardtimes
Well-known member
Hey olut,
Congratulations and THANKS for posting current results for our benefit !
I'm confused about your response though. You say...'new kork/neoprenes inserted'...which is it..did you use cork OR neoprene seal
Or is there a new seal mixing the two materials ? I ask, as I'm now in same situation as you...machined off slinger (bought that way) ?
olut
Member
Hi,
My original crankshaft had a slinger, which has been machined and removed. The seal made of kork/neoprene has been purchased at MAC's with part number 28-26022-1.
When you do same, make sure that new gliding surface for kork/neoprene looks like a mirror and check if this is 100% in center to the crankshaft mains.....
As a surprise now the front seal leaks a little, new gasket on its way from US to Vienna, minor issue. To complete the odysee of fixing incomplete renovations years ago by previous owner(s), now the corroded gas tank undergoes a fix, galvanic rost removal followed by chemical shielding...
...and then "mission completed after investing about 20.000,- (Euros)
Best Greetings
Albert
My original crankshaft had a slinger, which has been machined and removed. The seal made of kork/neoprene has been purchased at MAC's with part number 28-26022-1.
When you do same, make sure that new gliding surface for kork/neoprene looks like a mirror and check if this is 100% in center to the crankshaft mains.....
As a surprise now the front seal leaks a little, new gasket on its way from US to Vienna, minor issue. To complete the odysee of fixing incomplete renovations years ago by previous owner(s), now the corroded gas tank undergoes a fix, galvanic rost removal followed by chemical shielding...
...and then "mission completed after investing about 20.000,- (Euros)
Best Greetings
Albert
Walt Dupont--Me.
Well-known member
I've built a few and removed the crank slinger, used the one piece rubber seal that has to be installed over the end of the crank ( make sure there is no sharp edges on the back of the crank) But I've sort of given that up. I always remove the plug where the drain pipe screws in the cap, usually the pipe is screwed so deep it plugs half the hole. I use a rat tail file, chain saw file and file those threads inside the hole for a smooth flow of return oil, Also I think a 3/8 drill fits up that hole to make sure it's clean. You can bye those dish plugs, I forget the size, from about any parts store, I get Dorman brand. Of course my engines are all rebabbited and all balanced. I've been using the weld on counter weights the last few yr's, makes smoother engine and easier on the mains. Walt
hardtimes
Well-known member
Hey Walt,
You've got to post some pictures here of your A/B builds,eh
!You do nice work and post V8 finished product...but not fours ?
Question:
Sounds like you used the Burtz rear seal ('over end of crank' ). WHY did you stop using that (too much work ,machining of slinger or leaks or WHAT?). Can you show any pictures of rear cap and the 'plug' operation that you use. Thanks !