Engine bearing questions

Pamodelaroadster

Pamodelaroadster

Member
Hello, I’m new to model engines. I took the oil pan off to check things out, I was getting a lot of oil leakage out the rear main. Here’s a picture of the rear main,to me it looks like these are bearing inserts not Babbitt bearings and they cut an oil drain groove, several. The rear main had one shim on one side that is .007” thick. When I take it out and put the cap back on the engine is still not locked up. The rear crank journal looks very good to the naked eye.The crank end play is .004”. I didn’t get to the other bearings yet. Thanks for any comments!
 

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A fairly normal "homebuilt" rebabbit job. The X scribe is not done correctly - although what is considered "best" technique depends on who is doing the rebabbit.

The fact that the cap was as "unbalanced" as you found it MAY be the root cause of your leak. This one certainly a candidate for "plastigauge" and then figuring out the minimum EQUAL amount of shims required for each side.

The two sides of the bearing HAVE to have the same thickness in shim because it is the shim that "seals" the bearing against movement of the oil along the mating surface. Some shims have paper backings which can act to give the seal some "give" and allow perhaps one thickness to be removed from one side for optimal bearing tightness - and yet not make a wedge shaped "leak path."

Normally I would say this one should be 're-done' as a way to make sure it does not leak. Still, there are steps you can take which can reduce the leak-path beginning with equalizing the shims.

This might even involve a piece of paper cut to the thickness/outline of the shim and possibly one on each side - but this would be a "farmer fix."

You also want to check the other "seal areas" around your rear main to be sure they're "tight" against oil passage to the "slinger ring" area of the rear main. Most who have the oil pan off intuitively have this thought in mind while replacing the oil pan. Permatex is your friend.

Also keep in mind that ALL the lubrication the engine moving parts get comes from two sources: the dipper tray AND the oil pump.

Your dipper tray is ALWAYS full to the brim with the engine in operation. Your oil pan doesn't need to be so much. As long as the oil pump itself it covered - and I'm talking the oil pump itself - not the screen - then you're good to go. Theory says you fill the oil pan full to cover the pump screen. In real life you need to cover about HALF the screen - as long as the oil pump inlet hole is covered.

So you don't need to keep the oil pan filled "to the line." Rather a bit less, possibly QUITE a bit less oil is required.

Of course with less oil in the "reservoir" (what the oil pan is) then you'll dirty and stress that oil greater and quicker - a more frequent but less quantity of oil in an oil change perhaps?

Joe K
 
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Did you remove the oil drain tube or is it missing? You verified that the other shim is not still up there stuck to the block? End play at .004 is good, you should plastigauge the bearing to see what you have for clearance. :)
 
Looks to me to be Babbitt, not an insert and whomever cut those grooves had no clue what they were doing. That is not to say it is beyond saving.
Are you a member of a local Model A club? Is there an engine reconditioner nearby? They might be a good source of information on this. If, after the shim has been removed, there is still more than 0.001-0.0015" clearance, I've seen the cap ground down a little till it is right. The process involves a flat surface (like a sheet of glass) and wet and dry sanding paper. I'll leave it to others to explain/show how that is done.
 
As long as it gets oil you’re ok, the extra grooves actually reduce hydrodynamic cushion, but not enough to worry about.. you can dress a cap down on a lapping block but be aware you are making the bearing oblong, going tight in the center and letting it burnish works..

Or just pop the dough and get the mains repoured , it’s up to you.
 
When you put the cap back on to check the clearance, did you torque it to 55 foot pounds? If it was still loose then you had about 0.035 clearance or more which is too much and can lead to oil leakage out the rear main. As others have said, check to see if there is another shim stuck to the block.

The bearing is Babbett.

As others have said, use wet and dry paper on glass to lap off a little of the cap to get the proper fit, measured with Plastigage. Use a figure 8 motion for the cap on the sand paper. You can fit the cap to the bearing with yellow Timesaver.

Use a very thing smear of gasket sealer on the cap to seal it and prevent oil leakage.

Check the other bearings for proper clearance.

All this is best done with the engine out of the car and mounted on an engine stand. You can rig a Come-a-long to get the engine out or use two strong buddies with a 4X4 and chain. If you don't have an engine stand you can set the engine upside down on blocks so that the valves and pistons will not hit the blocks.

When putting the bearing back together use some assembly lube, which is a very thick oil. That will help with the initial startup.
 
I'm curious the same as Fathead is. Was the drain tube installed and you removed it or was it not there at all? It is not shown in your picture.
If it is missing that will cause a rear main leak.
 
There was definitely only one shim on one side. The drain tube was there. It was about a 3 inch piece of 1/8” pipe nipple, how long should it be?
when I put the bearing cap on I torqued the nuts to approximately 50 pounds and the crank still rotated. I will definitely be checking the bearings with plastic gauge. In the next couple weeks I’m going to be removing the transmission to put in a Mitchell and a lighter fly wheel so I may wait for the plastic gauging until the fly wheel is off, I really don’t want to pull the engine also right now if I don’t have to..
Thanks for all this great information.
 
The oil drain tube end needs to be immersed in the oil in the bottom of the pan so that pressure in the pan does not restrict the rear main from draining.

See https://www.snydersantiqueauto.com/product.htm?pid=983977&cat=41685

I know you are trying not to remove the engine from the car but in the long run it is much easier if removed and will save you time and effort. You need to have the engine vertical to correctly mount the flywheel and clutch. You will have to measure the flywheel housing and flywheel runout. The "red book" is very handy for instructions on how to do all this.

See https://www.snydersantiqueauto.com/product.htm?pid=980031&cat=41621
 
Check to make sure that the shim is not laminated. Take a sharp knife and see if you can peel off a lamination by starting at an edge. If not, either get a few thinner shims or a few out of thinner shim stock- use the one you have as a template. Yes, pulling a .007 shim from one side will most likely lock up the crank.
 
Dan McEachern said:
Check to make sure that the shim is not laminated. Take a sharp knife and see if you can peel off a lamination by starting at an edge. If not, either get a few thinner shims or a few out of thinner shim stock- use the one you have as a template. Yes, pulling a .007 shim from one side will most likely lock up the crank.
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He said that with the shim out, the engine was not locked up. Therefore, he needs less clearance yet. Separating the shim (heat it first with a hot air gun) also won't help.
I'd use the wet and dry paper and glass plate to take a little at a time off the cap. It is so little these concerns about the bearing being out of round don't matter. The other option is to have the main bearings repoured and line bored again with a few shims in each.
 
Be advised that there are some errors in the book, I think there is a list of corrections on this site if you look. It is a great book otherwise. :)
 
The oil groove in the bearing is a attempt at draining the oil out of the bearing as a method of “preventing” or reducing rear main leak.
Using aluminum foil for checking clearance can eliminate plastigauge interpatation problem and too old and hard problems, 1 layer of foil and crankshaft is still moving, ok,2 layers and tight
 
My own observation and opinion is that a babbitt journal bearing where there is a rotatable clearance with no shims at all is on it's last legs of serviceability unless the clearance is .002" or more. It still has a thrust face left but the wear is starting to get excessive. I'd be checking that center main. That's the one that is likely worn beyond specs with such wear on the rear main.

Since the babbitt coating on the cap is still all there, it's a testament to its capability to last. Many times the babbitt is cracked or flaking off when it gets thin so I'd be wondering what the crank journal size is and how much it has been turned down, if any, in past engine overhauls. The smaller the journal is, the thicker the babbitt has to be to work with it. There are limitations on how far a crank can be turned down on the small journal engines.

A person can use odd and even stack ups on journal cap adjustments. To have a .007" shim only on one side is too much though. I'd try to work with .002" shim laminations or less if possible but super thin shims can get beat out if the bearing starts to get loose. A lot depends on what the shim is made from too.

Most of the folks that still do babbitt journal bearing replacement work have fixtures to cut the oil grooves properly. Too many grooves just leads to more rapid wear and lubricant leak down in service. The job should be done the way Ford did it for best lubrication and longevity of each bearing assembly.
 
Dan McEachern said:
Check to make sure that the shim is not laminated. Take a sharp knife and see if you can peel off a lamination by starting at an edge. If not, either get a few thinner shims or a few out of thinner shim stock- use the one you have as a template. Yes, pulling a .007 shim from one side will most likely lock up the crank.
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Whoa! Back up the bus a bit! In the first post he removed the .007" shim, reinstalled the cap and the crank still turned. So why mess with splitting the shim pack?
 
First thing I would recommend is checking the clearance with fresh Plasti-gauge. I happen to like .0015". So let us know what you have before pulling the motor.
 
Patrick L. said:
First thing I would recommend is checking the clearance with fresh Plasti-gauge. I happen to like .0015". So let us know what you have before pulling the motor.
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Isn’t Plastigauge thought to give unreliable readings when the motor is still in the car?
 
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