Rear Main Seal

[n1gzd_plymouth]

Because I have too many projects and because I suspected that the oil leak issue on my 1936 Plymouth (with A 52 Dodge 230) is a can of worms I hired a good mechanic solve it for me.

My suspicion was that I did not have a simple leaking rear main seal (leak was getting too large).

 

Upon inspection he discovered that the previous owner added a copper shim at each side of the end-cap. He removed these shims and confirmed that without them it fits too tight. I think that this end cap is from another car (parts bin build?). Anyway, it appears that the leak is caused by the shim creating a gap in the seal fitment.

 

He is going to check the fitment with some plastigage and get back to me (it could be adjusted depending on where it is too tight - one side or everywhere).

 

If it cannot be made to fit without machine shop then we are done I and I pull the engine.

Question: Has anyone ever discovered a hack to at least fix this temporarily (knowing that it needs to be fixed right later)?

 

I have another question. Lets say that i did not have this end cap/bearing fitment issue and I just had a leaking rear main seal.

 

It appears that it is just about impossible to change the top half of the seal with the engine in the car. If you remove the transmission and flywheel it would be easier but there is not a lot of clearance to get to the three bolts that hold in the upper seal. Even with these things out the crankshaft flange clearance and getting at the top bolt might still be hard.

 

Here is my question: Do most people just change the bottom half because it is where most of the oil will leak (due to gravity) and wait to change the top half next time the engine is out?

 

Thanks,

Rebecca

[n1gzd_plymouth]

[n1gzd_plymouth]

[keithb7]

I too am interested in learning more here. I too have a pretty good rear engine leak. I’ve yet to get in there. Please do post pics and update us as you figure this out and fix it. Thx. 

[kencombs]

Take a look at the back of the bearing shell to see if it is marked with an undersize.  it used to be quite common for guys to fit .001-.002 or even, rarely, an .005 undersized bearing to compensate for wear.  It's possible that the last person in there bought a set of undersized and discovered one journal wasn't worn enough, thus the shims.

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[n1gzd_plymouth]

It is standard. Time to pull the engine. Needs to be line bored to right size.

Rebecca

[Bbdakota]

I don't believe I've ever heard of shimming a main cap. Was this common practice back in the day? I would think not.....it doesn't work in theory. How does the line bore stay true.....puzzled! 

[Sharps40]

Shimming was SOP for babbit berings.   For insert, most all manuals at the time instructed against it.  In this case, I'd do two things.   Fit a proper size bearing with no shims if at all possible and pull the rear seal and put on a new one....woops, just read your post, seems you are rebuilding so its moot.

Edited August 27, 2019 by Sharps40

[bones44]

check out best Gaskets for rear seal

[n1gzd_plymouth]

1 hour ago, Sharps40 said:

Shimming was SOP for babbit berings.   For insert, most all manuals at the time instructed against it.  In this case, I'd do two things.   Fit a proper size bearing with no shims if at all possible and pull the rear seal and put on a new one....woops, just read your post, seems you are rebuilding so its moot.

I think that the issue is that the bearing is correct but the endcap was from other engine (needs line boring to this engine). Anyway, enough anomalies that we think that we wasted enough time. time to pull it. thanks for your comments.

[n1gzd_plymouth]

4 hours ago, kencombs said:

Take a look at the back of the bearing shell to see if it is marked with an undersize.  it used to be quite common for guys to fit .001-.002 or even, rarely, an .005 undersized bearing to compensate for wear.  It's possible that the last person in there bought a set of undersized and discovered one journal wasn't worn enough, thus the shims.

 

I see. It is marked std. but as noted, i my recent post we are giving up on any hacks and pulling the engine.

Rebecca