Rear main leaking oil

[BrianH]

My rear main is leaking oil badly. Babbitt bearings are newly done. It will put a 12-to-18-inch circle of oil on the ground after about 20 minutes of running. I found that the bearing has about 4 thousands clearance. Would that in itself cause it to leak like it does? Yes, the drain tube is in place. Thank you all in advance for your thoughts. Brian

[Bob Bidonde]

An oil level at the full mark of the dip stick will result in extraordinary oil leakage. Typically, the oil finds its own level midway between the "F" and"L" marks. Also, the dipstick does not indicate oil in the dip tray of the oil pan, so when changing the oil, only put in 4 quarts.


0.004" clearance is a bit excessive for newly babbitted bearings, but not enough to cause extraordinary oil leakage. Also, the fore-aft play of the crankshaft is important and should not exceed 0.006" on a fresh engine.

Other causes I have found over the years of playing with engines:
> Wadding the re-builder uses to keep babbitt from running out during the pour is left in the bearing drain;
> Rear main drain tube screwed too far into the bearing such that it blocks oil flow;
> Wrong diameter drain tube. It should be 3/8";
> Lack of sealant around the bearing bolts;
> Wrong type of shims;
> Cracked babbitt;
> Improper oil pan gasket fit & cork seal fit at the rear main bearing;
> Loose oil pan bolts;
> Clogged crankcase breather.

Another source of oil leakage is the transmission. Excessive oil and unsealed front bearing will contribute to the puddle.

[Patrick L.]

Yep, oil level is important. Too much will cause a leak. Some engines have the wrong or mismarked dipstick.

.004" is a lot, especially on a new engine. I believe this can be a cause of leakage. I set the rear mains at no more than .0015".

[BrianH]

This is a new rebuilt engine. First time putting oil in it. I put one quart of oil down the distributor hole and four quarts in the oil fill tube.

[arnhemmer]

I would contact the rebuilder.

[nkaminar]

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Bob has all the reasons listed. The clearance in the rear main is excessive. Take the dip stick out when running to see if vapor pressure is building up in the engine. It will take some work to figure this out. Arnhemmer has the right response: take it back to the builder. Do you have the correct filler pipe and breather with no foreign material added, like steel wool?

[BrianH]

Oil filler pipe is clear. Cap is clear as well. Yes, Bob has a good reply. Thank you Bob

[PC/SR]

Agree .004 is too much clearance. I run between .0015 and ,002. You might be able to fix it be removing shims and measuring. Check end play while you are at it. .008 is max per ford specs. Should be around .004 on a new engine.

[Y-Blockhead]

In addition the what Bob Bidonde listed it could be leaking out the back of the camshaft if the flywheel housing gasket is leaking or installed incorrectly.

[Conaway2]

I agree with post #9…missing or. Gasket installed backwards will cause exactly what you describe. Don’t ask me how I know……

[old ugly]

make sure the crankcase is vented properly. and not building pressure. oil filler cap.

[old ugly]

ditto on #9

and

never shim that area with metal shims (which is done for bellhousing runout)
if it needs a shim to make the bell housing true i cut another gasket for there, shorter and back up the existing gasket, this acts like a shim.
a metal shim there will create a leak.

[gdmn852]

.004 does seem like too much clearance, in a new engine, I would contact the rebuilder before doing too much and see what they say.

[BrianH]

So, I got under the car tonight and removed the rear main cap. Sure enough I screwed that return tube all the way down. Which caused it to block the oil passage about 3/16th. My next issue is that cap does not have very good threads for that tube. Should I use Loc-tite? Or J-B Weld? Or???

Tomorrow night I'll plastic gage that bearing and adjust shims as needed. I should do them all, I guess.

Anyway, it looks like I caused my own problem. Thank you to all for your thoughts.

I also heard that you can't get the rear main cap off if you have a counterweighted crankshaft. I got mine off without too much trouble.

[Kurt in NJ]

Since you have the cap off take a picture of the bearing surface, do the oil wells go all the way to the ends?

[old ugly]

i was looking something else up and found this.
i didn't know why the cover on my multi disc bell housing didn't have louvers. oil leaks were an issue rite from the start.