Rear Main oil Leak,with full pressure system

[29restorod]

I just bought a 29 Coupe,with a "Touring engine",and it leaks way too much oil from the rear main. The guy that built the engine,has passed away,as well as the last owner. I know it has a modified oil system,because it idles at 10# pressure,and has 30# at cruise speed. When I was young (a long time ago),My Model A broke the rear main oil return pipe,and leaked just like this one. That was caused by me trying to pull a hole shot. I have also heard that increasing the oil flow,to a Slinger type crank,overwhelms the drain back systems. Is it nessary to install a rear seal,when modifing the oil system,or do I have another missing drain pipe?

[Jim Brierley]

You will have to pull the pan to see if the tube is intact. If so, it would be best to install a seal. I've had good luck with the Burtz but the engine needs to come out to install them. There are others on the market that may work well too?

[29restorod]

This Burtz seal,does it require machine work on the crank or block?

[just plain bill]

Originally Posted by 29restorod

This Burtz seal,does it require machine work on the crank or block?

Yes it does. Why don't you pull the pan and see what you have?

[Jordan]

To me, I wouldn't think a model a engine would need 30# pressure. This is just a guess because I've never dealt with a pressurized oiling system, but if there would be too much pressure, maybe it would blow out the real seal? Just a guess.

[29restorod]

Sponsored Links (Register now to hide all advertisements)

We went to a cruise night,tonite,and I checked under the car several times. While the engine is running,it does not leak ( I let it idle for a long time). After shutting off the engine,it leaves a puddle about 6" in diameter. This engine does have Siemens High Power head,(compression ratio,unknown),and a B cam. This may be why the builder went to a pressure system.

[James Rogers]

Sounds like the tube is missing. My Cabbie lost the tube once and leaked just like this. When it was running it never leaked but shut it off and it left a 6" puddle every time. I would check the masin and see what it has. If it has a Burtz seal and it is leaking it may be damaged or the tube might be missing. If the seal is damaged and you want to replace it I sell a seal that has been really good for stopping leaks and will replace the Burtz seal exactly and is a 2 piece item so it is easier to install.

[Cajun]

AutoZone sells a dye that you can put in the oil. They will lend you a black light to look for the leak source.

I had a similar leak. When the engine was line bored for the mains inserts, they cut into the threads of the bolts that hold the crank in. This puts pressure on the threads. The read main bolts can leak on the nut side and bleed out in the area of the rear seal. The dye will show that.

[29restorod]

The last owner was just here,with his friend that stored the car last winter. They stored the car in a trailer,with a tile floor,and found no oil. He has no large oil spots at his house either. I am hoping it is just the oil tube fell out. As soon as I get a gasket set I will pull the pan.

[Jim Brierley]

when you have the pan off, check to see if the system has been converted to full pressure. If so, you need 30 psi in order to feed oil to the rods, thru a drilled crank.

[29restorod]

Today I finally got the oil pan off. The oil drain tube was still in place. I was bummed out,I thought I had an easy fix,for the leak. Tomorrow I will remove the the rear main cap,to see if there is a seal or just a slinger. If there is a seal,the engine must come out. If no seal,then I will check out the oil lines in the valve chamber.The connecting rods still had their dippers in place. I have never seen a pressure oiling system. I assume there is tubing connecting the mains,and some weep holes to supply everything else in the valve chamber. I will take pictures if I can't figure it out.

[29restorod]

Well it seems I don't have a full pressure system after all. Took off the rear main cap today, and the valve cover. There is no seal in the rear main,and no pressure lines inside the valve area. I am wondering how I can have such high oil pressure? Any ideas where I should go from here? Is the pump putting out too much oil? Would installing a filter in the cam cover reduce the oil pressure?

[Tom Wesenberg]

In your third picture, maybe it's the shims, but I don't see the oil slinger setting deep in the pocket like it should be.

[29restorod]

I just checked in a book I have here,and the pictures of the slinger,in the groove, match my pictures.

[callcoy]

I would think that in order to have upwords of 30#, the oil pump would have been modified. The intake would have been enlarged and the top of the pump where the two notches were milled would have to be filled in. This filled in mod greatly reduces the amount of oil to the pump drive and center cam bearing thereby increasing the operating pressure. But doing this also reduces the amount of oil to feed the mains and the dipper tray. I would doubt that the pump has been modified, on a "A" a whole lot of other things have to been modified and installed to use a full pressure pump. Hindsight would have been to double check the pressure with a second gauge, but then you didn't know then what you know now. The "A" engine with 30# of oil pressure, to me, is like one that gets 65 miles per gallon. I am most interested in your findings!
Steve - Santa Rosa

[29restorod]

I hate to put it back together without knowing what is causing the problem. A friend of mine that restores a lot of "A's said he has found new rebuilds that leaked,and he cured the problem by refitting the main cap(blueing,scraping,and shims). The pump looks brand new,and stock on the outside. I may open it up to take a look,and I was thinking of trying another known stock pump.

[just plain bill]

Originally Posted by 29restorod

I hate to put it back together without knowing what is causing the problem. A friend of mine that restores a lot of "A's said he has found new rebuilds that leaked,and he cured the problem by refitting the main cap(blueing,scraping,and shims). The pump looks brand new,and stock on the outside. I may open it up to take a look,and I was thinking of trying another known stock pump.

Check, if you can, the end play of the crankshaft. Too much endplay will allow the crank to act like a pump forcing oil out of the rear main.

[Jim Brierley]

In order for pressure to build up over a few pounds, there must be a restriction down stream somewhere. The A pump, or any gear type pump, will pump 100 or more psi IF RESTRICTED. In the stock A system there is no restriction, it just dumps it all into the valve chamber.

[Kohnke Rebabbitting]

Originally Posted by 29restorod

Well it seems I don't have a full pressure system after all. Took off the rear main cap today, and the valve cover. There is no seal in the rear main,and no pressure lines inside the valve area. I am wondering how I can have such high oil pressure? Any ideas where I should go from here? Is the pump putting out too much oil? Would installing a filter in the cam cover reduce the oil pressure?

.006 is max for end play, and that is wore out to me. We set up at .003 Min., and .004 max, normally .003, as I hand scrape the last .002. After you remove .006 thousands from a new babbitt job, your bearing hole being egg shaped, and is ready for new babbitt. The reason being the large clearance on the side, will release much more oil, and the rods throws the oil up under the pistons, and is more then the rings can handle, and it can be even a low milage motor. When you have oil pressure added to the mix, the problem gets much worse, so the main cause of oil burning, is over clearanced BERAINGS. There are rebuilders that miss boring clearances, on the to large side, and and then pull shims to close up the gap. The more egg shaped, the more oil is lost, and the rear gets more then it can handle. So, you need the right clearance, end play, sealer on the shims, as oil will run through them, main bolts have to also be sealed, when the babbitt is set up for align bore, the first place to start is, your align bore center has to be exactly between the bolt holes, if not, the shims will not be centered, and,or the Aluminum slinger, and do not use the old one over, as they can be wore quite wore. After the bore is centered, that setting should not be moved again, unless it does. Many times the pipe hole in the cap is pluged from babbitt, hole pluging material, and the oil pipe it's self. We always pull the soft plug, when rebuilding. Herm.

[ctlikon0712]

Could be that the oil fill cap gets installed on too tight and after shut down the crank case pressure that isn't getting vented pushes the case oil up the tube and out throught the rear main. Johnathan had this problem on www.365daysofa.com

[TinCup]

Yes any restriction from the oil cap will cause the pressure to build. Someone had put steel wool in mine to help with blow by and my coupe would do exactly as described.

[29restorod]

All Good information. I did not know that the shims needed to be sealed,or the rear main bolts. I know that my bolts are loose,when not torqued down,also the shims are clean. Remember,this engine leaks mostly at shut down. I pressure flowed solvent through the drain pipe,and it flows fine,even gravity feed,it pours out the bottom as fast as you pour in the top. I will check the oil fill cap(sure would be nice if it was that simple).

[Dave in MN]

From 29restorod…“While the engine is running, it does not leak ( I let it idle for a long time). After shutting off the engine, it leaves a puddle about 6" in diameter.”

I know I’m stating the obvious but it points to not only the source but the possible causes of your leak. The oil leak you describe is from oil draining down from the valve chamber into the rear bearing after shut-down. The crank is not riding the “oil pulse” when static so let’s assume it settles to rest on the cap oil film leaving additional clearance at the top. With the extra clearance at top, the oil drop tube from the valve chamber is given more room to flow the available oil over the crankshaft surface. Most of this oil moves along the top and sides of the crankshaft and runs up against the rear thrust of the crankshaft. From this point it forces its way in all directions as it has a fair head of pressure equal to the height of oil in the rear galley of the valve chamber. Any gaps around the rear oil seal near the parting line of the bearing will flow oil to the outer edge of the rear cap and will leak into the flywheel housing. From my experience with oil leaks after shut-down, the leaks are from a dry set rear seal, lack of sealant at the cap parting line and excessive clearance between the shim pack and crankshaft.
Without removing the engine from the car I would check all of the following:
1) Remove the oil drain tube from the rear main cap and through the threaded hole in the rear main cap, insert a small punch and tap the oil passage plug out. Clean the oil return passage in the cap with the correct size drill bit. Don't use a drill motor unless you are very careful. It will bind as it bottoms out. There should be an opening to the oil return passage from both cap grooves. Check that they are not obstructed with babbitt. Replace oil passage plug and drain tube. If any portion of the passage is restricted it may not have the required capacity needed for your engine at shut down.
2) From your picture the end play gap appears to be excessive. (Unless that’s a shadow or oil accumulation line.) As Herm said....006" or more may be a problem. Can you set up a dial micrometer and force the crankshaft back and forward to check your clearance? Feeler gauges do not work well in this location.
3) Use a small amount of sealant on both sides of the shims during assembly and make sure the shim packs are against the crankshaft as you pull it tight.
4) Check your bearing fit with Plastigage. Check it in the direction of the crank center line. Your fit should be about .001 to .0015" Clean it up and then lay a long piece of Plastigage at a 45 degree angle on the crank so it will wrap almost to the surface of the block, tighten and then check. This will tell you if the bearing fit is oval. If the clearance increases considerably as it approaches the parting line...it's oval. If oval, you will flow greater amounts of oil near the parting lines of the cap and without sealant, it may pass over the edges of the cap.
5) Look at the third picture you posted. You will see a gap between the block and the rear seal. This gap extends beyond the shim pack on the right side of the picture. If the rear seal is damaged or not set in sealant, oil will pass around it and leak at these gaps. You could try cleaning the gap with carb cleaner and sealing but if the seal is dry set, it would likely leak around the perimeter anyway.
If you remove the engine.
Check the condition of the rear oil seal in the block. If deformed or not set in sealant it may leak as you describe after shut-down. Replace with a good original or a new one. Fully bed it in sealant and make sure the gap between the block and the seal is filled at the parting line.
Good luck with reducing the leak! Let us know if you slow or stop it.
Good Day!
Dave in MN

[29restorod]

Checked my oil fill cap last night,no way can that seal the fill tube. It has 4 horizontal tabs,that keep it from seating on the tube,it is all open above those tabs. Will work on the rear main cap tomorrow,with plastigauge,shims,and sealer,and check end play.

[MikeK]

This won't address your rear main leak, but the 10psi idle and 30psi running should not happen. There is likely a restriction somewhere in the block bore between the oil pump and the dizzy drive gear, or the drive gear and the end of the oil tube at the chamber base. This was a common mod to force oil out the hole where your gauge is now attached. The oil would go to an external remote filter and then back to the valve chamber. While you have the pump out, pull the dizzy drive gear assembly and investigate for mods. Also check the cast-in-place tube along the bottom front of the valve chamber. It should be completely full-bore and open all the way into the big bore the pump shaft fits into with the dizzy drive.

[Benson]

Sponsored Links (Register now to hide all advertisements)

1. In picture #1 sure looks to me like the groove leading to the oil drain tube under the cap is full of babbit slag. This condition will cause oil to run out the rear main cap because it can not run down the drain tube and into the pan. Most likely the drain under the babbit is plugged up also. Need to remove welch plug and check that also.

2. As others have mentioned ... If someone plugged OR RESTRICTED the oil tube that leads forward to oil dam number 1 (front) then pressure will be high like you have here. People plug this pipe so they can tell everyone they have 30 lbs oil pressure. It only starves the rods and leads to rod failure because dipper pan runs dry or at least level is too low.

Model A oil system relies on VOLUME not pressure. Plugging the pipe sure will give you pressure but there is only limited oil getting to dipper tray.

[29restorod]

BENSON, Thanks for that information. I will look there tomorrow,for a restriction. I know that won't have any effect on the oil leak. If I find a restriction,then I won't install the oil filter kit I ordered yesterday.

[MikeK]

Originally Posted by 29restorod

BENSON, Thanks for that information. I will look there tomorrow,for a restriction. I know that won't have any effect on the oil leak. If I find a restriction,then I won't install the oil filter kit I ordered yesterday.

Why not remove the restriction and go with the filter? A clean engine is a happy engine.

[29restorod]

What I meant was,if I find a restriction,I will remove it,and not use the oil filter. My thinking was the oil filter would lower the oil pressure from a high out put pump,but thats not what I need if there is a restriction,after the pump.

[29restorod]

Today I checked Rear main clearence. It was .003",so I peeled off one shim. The next check came out .0015". I then used a thin coat of 3H sealer on the bottom of the shims. Then placed a very small bead of #1 sealant around the outer edge of the main cap. Crank shaft end play is .006",nothing I can do about that at this time. I then removed the oil pump drive gear,to look for a restriction,none found. I took the oil pump apart,and found no modifications,except the bottom cover gasket was not there,I installed one. It will be a few more days before I finish this project,as I need to work on the carb also.

[thepolecat]

Keep me posted on this as I am having the same issues and I am following you fix for fix on mine.

[Milton]

Originally Posted by 29restorod

I took the oil pump apart,and found no modifications,except the bottom cover gasket was not there,I installed one.

FYI The removal of the bottom gasket and lapping the cover and gear bottoms is part of the modifications to a stock pump to increase oil pressure. The volume is increased by modifying the inlet and outlet holes.

[29restorod]

Success at last. Today I got everything back together,and fired up the engine. After a five mile drive at 45 MPH,I parked on the cement drive with the engine running for a few minutes. No leak while running,then shut off engine,and checked after 30 minutes,one drop. After 2 hours a small circle about 2" in dia,on a metal drip pan. Nothing from the front seal. I can live with that amount of oil leakage. The oil pressure was about the same,maybe a little lower,about 10 pounds at 45. I installed the bypass oil filter,in the front timing cover,and installed a gasket on the pump gear cover. I am now using Rotella diesel oil,which is what I run in my flathead V8's. I don't know what oil the previous owner had in it. The only thing I did,that would have any effect on the leak,was to set rear main clearence,at .0015",and seal the seam between the cap and the block,with #1 permatex.

[1931 flamingo]

Nice feeling isn't it. I don't envy anyone with the rear main oil leak. I seem to be very fortunate that mine doesn't leak. At a show earlier this year parked next to a very nice 31 deluxe roadster that the newbie had purchased last year for about 25K, asked me in a low whisper with hand over mouth if mine leaked? Said nope, got down and looked under both cars, nothing under mine, he had about a 3 inch circle. I felt for him.
Paul in CT

[pilotdude]

Hi Guys

I also have a leak into the flywheel housing. I pulled off the main cap and there was minimal sealant. I did notice that there were no shims> what is the purpose of the shims on the main cap? the channel in the cap is clean although there was nothing connected to the thread on the cap??

I also see there is no oil pump cover gasket.Could this be part of the problem?

Regards

Kevin

[CarlG]

Originally Posted by 1931 flamingo

Nice feeling isn't it. I don't envy anyone with the rear main oil leak. I seem to be very fortunate that mine doesn't leak. At a show earlier this year parked next to a very nice 31 deluxe roadster that the newbie had purchased last year for about 25K, asked me in a low whisper with hand over mouth if mine leaked? Said nope, got down and looked under both cars, nothing under mine, he had about a 3 inch circle. I felt for him.
Paul in CT

Mine only seems to leak when away from home. I can place absorbant pads under mine in the garage and get narry a drop. But park it in my friend's driveway and there's a leak the size of the BP Gulf fiasco.

[James Rogers]

Originally Posted by 29restorod

Success at last. Today I got everything back together,and fired up the engine. After a five mile drive at 45 MPH,I parked on the cement drive with the engine running for a few minutes. No leak while running,then shut off engine,and checked after 30 minutes,one drop. After 2 hours a small circle about 2" in dia,on a metal drip pan. Nothing from the front seal. I can live with that amount of oil leakage. The oil pressure was about the same,maybe a little lower,about 10 pounds at 45. I installed the bypass oil filter,in the front timing cover,and installed a gasket on the pump gear cover. I am now using Rotella diesel oil,which is what I run in my flathead V8's. I don't know what oil the previous owner had in it. The only thing I did,that would have any effect on the leak,was to set rear main clearence,at .0015",and seal the seam between the cap and the block,with #1 permatex.

You probably could have removed a shim from both sides and had a tolerence closer to a true .0015. The flywheel will give a false reading when using plasti-gauge because of the weight. Still, sounds like you found the problem and at least solved it for the most part.

[pilotdude]

Originally Posted by James Rogers

You probably could have removed a shim from both sides and had a tolerence closer to a true .0015. The flywheel will give a false reading when using plasti-gauge because of the weight. Still, sounds like you found the problem and at least solved it for the most part.

Hi guys what is the clearance you are talking about. As I said before mine has no shims so what must I be measuring.

tks

[James Rogers]

Originally Posted by pilotdude

Hi guys what is the clearance you are talking about. As I said before mine has no shims so what must I be measuring.

tks

With no shims, you don't need to measure anything. You don't have anything to be able to adjust with so it is a useless exercise. Sounds like the mains are most likely ready for replacement. However, to answer your question, there should be a clearance of .0015 or one and a half thousands between the bearing surface and the crank journal. This clearance allows the crank to ride on a wedge of oil when the motor is running and slows the oil flow when stopped so the drain can keep up with the flow from residual oil in the valve chamber as it tries to return to the oil pan. If the clearance is too big or the thrust is loose, oil will overwhelm the tube when the motor is stopped and the well at the slinger will fill and overflow. The result is the dreaded oil leak.
Hope this helps you to understand what is happening to your motor.

James.

[pilotdude]

Originally Posted by James Rogers

With no shims, you don't need to measure anything. You don't have anything to be able to adjust with so it is a useless exercise. Sounds like the mains are most likely ready for replacement. However, to answer your question, there should be a clearance of .0015 or one and a half thousands between the bearing surface and the crank journal. This clearance allows the crank to ride on a wedge of oil when the motor is running and slows the oil flow when stopped so the drain can keep up with the flow from residual oil in the valve chamber as it tries to return to the oil pan. If the clearance is too big or the thrust is loose, oil will overwhelm the tube when the motor is stopped and the well at the slinger will fill and overflow. The result is the dreaded oil leak.
Hope this helps you to understand what is happening to your motor.

James.

Hi James

Thanks for your reply.

I should give some history. The motor was rebuilt about 10yrs ago and has only done around 100km since then.
I have attached some pictures(not all the best quality)
there is some damage on the main cap where the sump cork gasket fits but i am sure nothing was leaking from there.
As you can see there is no tube attached at the end of the drain slot. What does the tube do?

regards

[Tom Wesenberg]

Welding a tube in place may fix the leak. I wonder why you have no shims with so few miles on the rebuild?

[29restorod]

Where your drain tube should be,looks bad. Looks like a large chunk of iron has broken away. It may not be possible to get a tube to stay in place. The tube acts as a syphon,without it a lot of oil will flow over the slinger groove. I had that problem when I was a teenager,after I tried to spin the tires. The tube broke off,from the crank flexing. I never did that again. I started this thread thinking I had a full pressure system. As it turned out I did not have one.

[pilotdude]

Looks like Il have to order one and see if it can be welded in place.
I have purchased parts from Macs before, is there anywhere else anyone can suggest.

Kevin

[Tom Wesenberg]

Originally Posted by pilotdude

Looks like Il have to order one and see if it can be welded in place.
I have purchased parts from Macs before, is there anywhere else anyone can suggest.

Kevin

Bert's and Bratton's and most other supply houses would have a replacement tube. Be sure to order the right sized, as they came in two diameters. Using MIG you should be able to weld it on without overheating and melting the babbit. After welding or tacking the pipe in place, if you still don't quite have it air tight, then apply a bit of JB Weld to the clean dry surface.

[jdpalmer]

Hey I just put an engine in that was rebuilt 10 years ago and wasn't installed in a car. I have the same oil leak. do you have more info on the two piece seal. Jim [email protected]

[pilotdude]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by jdpalmer

Hey I just put an engine in that was rebuilt 10 years ago and wasn't installed in a car. I have the same oil leak. do you have more info on the two piece seal. Jim [email protected]

Hi I will let you know if I solve the problem. I personally think installing a modern seal may be the best option in the long run

[James Rogers]

Originally Posted by pilotdude

Hi I will let you know if I solve the problem. I personally think installing a modern seal may be the best option in the long run

To be able to use any of the current or ancient sealing systems the crank has to be removed and the slinger cut off on a lathe. Not a job for the home hobbiest.

I would get a tube and screw it in and just spot it to the cap with a mig welder and cover it with JB Weld to seal it and help keep it stable. I don't know why you don't have any shims with a virtually new motor and the grooves look bad and are incorrectly cut.

[Benson]

Pilotdude's question:
"I should give some history. The motor was rebuilt about 10yrs ago and has only done around 100km since then.
I have attached some pictures(not all the best quality)
there is some damage on the main cap where the sump cork gasket fits but i am sure nothing was leaking from there.
As you can see there is no tube attached at the end of the drain slot. What does the tube do?"



I will give this question a shot here. As has been discussed here, the oil from the rear of the rear main runs into the Aluminum or pot metal "seal", (as it is sometimes called), then through a hole drilled under the Babbitt to the threaded pipe hole in the front of the rear main cap.

At this point the hole that the pipe goes into is above the oil level in the pan and is exposed to the air pressure inside the crankcase. If you leave the pipe out of the picture,the oil is forced by the crankcase air pressure, back up the hole under the babbit, over the edge of the "seal" and into the flywheel housing and onto the floor.

Using the pipe moves the opening down 3 or 4 inches into the oil pan, below the oil level so the air pressure can not force the oil out of the engine.

Remember Tom W's suggestion to seal the area around the tube with JB Weld? You do not want any air leaks here.

Hope this solves the mystery!

Note: Anytime welding is done near an open engine it is a good idea to cover any Babbitt bearings, camshafts and etc with a wet shop rag. This will keep any sparks from landing where you DO NOT want them. After it cools a small piece of metal is left there to scratch the bearing and embed itself in the the bearing to create havoc when the shaft starts turning. You may ask how I know this ... but I might just say "HUH?"

[jdpalmer]

Again I just put a rebuilt engine in and had the same problem of oil leaking after stopping. I thought it was coming from the rear seal but it was a crack in the flywheel housing below the cam and evidently the gasket was not sealing around the cam. [email protected]

[Kohnke Rebabbitting]

Originally Posted by Tom Wesenberg

Welding a tube in place may fix the leak. I wonder why you have no shims with so few miles on the rebuild?

Also, has lead Babbitt. Herm.

[Kohnke Rebabbitting]

Originally Posted by jdpalmer

Hey I just put an engine in that was rebuilt 10 years ago and wasn't installed in a car. I have the same oil leak. do you have more info on the two piece seal. Jim [email protected]

Better look deeper than a seal. Herm.

[George Miller]

Originally Posted by 29restorod

Well it seems I don't have a full pressure system after all. Took off the rear main cap today, and the valve cover. There is no seal in the rear main,and no pressure lines inside the valve area. I am wondering how I can have such high oil pressure? Any ideas where I should go from here? Is the pump putting out too much oil? Would installing a filter in the cam cover reduce the oil pressure?

Looks like you have a bunch of babbitt in the cap where the slinger should be running.