• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

273- Rear main seal leak fix?

Mark Barnes

Well-Known Member
Local time
11:01 AM
Joined
Mar 21, 2020
Messages
593
Reaction score
816
Location
MI Thumb
Started the 273 for the first time today. Came in a Belvedere ll that I bought sight unseen. Motor RAN, but pretty crappy. Kinda boggy, felt like it was running on 7 cylinders, maybe 6.
Anyway, it ran for about 2 minutes and dumped about a pint of oil in the driveway. My questions are as follows-
are 273's prone to rear main leaks?
The seller said he fired the motor for the first time, ran it for about 20 min at +1500 rpm, turned it off and changed the oil. Second time he tried to fire it he couldn't get it to idle and it dumped oil out the rear of the engine. I haven't gotten into it yet. I assume it's the rear main.
Is there reason it would be blowing oil out at a pretty good pace?
Can you replace the rear main seal like we used to, pulling the main cap and pushing the old one out/ cramming in a new one behind it? Did I read it may help to offset the seals from the 180 deg. position?
Any help would be appreciated...

20200330_162811.jpg
 
Last edited:
Can you confirm that it's not coming from the oil pressure sending unit and trailing down at the back?
 
^^^^ This.
A pint or quart that fast doesn’t sound like RMS. That’s a lot of oil with no real pressure.
 
Could be a oil pressure sender. Rear main's can pump some oil. The originals were a rope seal and can leak like a sieve after 50 years.
 
Could be a oil pressure sender. Rear main's can pump some oil. The originals were a rope seal and can leak like a sieve after 50 years.
Motor just got put back together. Older gentleman had the work done in CA before I bought the car. Crank grind and bearings, hone, re-ring, new cam and bearings, valve job, new carb, etc. Fired it up, supposedly ran it, leaked oil, and he threw in the towel....maybe. I can verify that it does run poorly, and compression test is next. I was kinda hoping it would be something simple I could fix. I'll check the sending unit. The only way it could be dumping that much oil is if there ISN'T one installed.
 
Motor just got put back together. Older gentleman had the work done in CA before I bought the car. Crank grind and bearings, hone, re-ring, new cam and bearings, valve job, new carb, etc. Fired it up, supposedly ran it, leaked oil, and he threw in the towel....maybe. I can verify that it does run poorly, and compression test is next. I was kinda hoping it would be something simple I could fix. I'll check the sending unit. The only way it could be dumping that much oil is if there ISN'T one installed.
My brother's 273 in his 66 Coronet ran like crap when he first got it shipped to his house. Had a dead cylinder. While checking it over I saw that the dead cylinder was due to the po trying to adjust the rocker arms and had that particular exhaust valve adjusted that it wasn't able to seat. After readjusting all valves (among other things) it runs perfect 12 years later.
 
Could be a oil pressure sender. Rear main's can pump some oil. The originals were a rope seal and can leak like a sieve after 50 years.
With all the rebuild work that was done to it the rms had to be replaced. At least I would hope so.
 
My brother's 273 in his 66 Coronet ran like crap when he first got it shipped to his house. Had a dead cylinder. While checking it over I saw that the dead cylinder was due to the po trying to adjust the rocker arms and had that particular exhaust valve adjusted that it wasn't able to seat. After readjusting all valves (among other things) it runs perfect 12 years later.
That was my first thought, valves out of adjustment. Valve covers come off as soon as I can get to it.
 
1. I was wondering why a lot of threads ask about oil coming from the oil sending unit? It's a pretty "dumb" part. Do they fail that much?
2. Is there a oil filter adapter on the 273 that uses a gasket, like some other SB's?
 
1. I was wondering why a lot of threads ask about oil coming from the oil sending unit? It's a pretty "dumb" part. Do they fail that much?
2. Is there a oil filter adapter on the 273 that uses a gasket, like some other SB's?
The pressure sender in screwed into the rear China wall by the distributor on the passenger side. Yes they can leak oil down the back of the block around the rear main seal area. As much oil is leaking out, it should be pretty easy to find out where it's coming from. The filter adapter in on the passenger side and can leak as well. It's not in the rear main area though. There are screw in oil galley plugs on the back of the block but rarely leak. Back of the intake can leak and run down the back of the block too.
 
Remove your flywheel/torque converter cover to see if the oil is coming from the back of the block. With that big of a leak on a new engine, makes me wonder if the cam plug isn’t missing.
 
1. I was wondering why a lot of threads ask about oil coming from the oil sending unit? It's a pretty "dumb" part. Do they fail that much?
2. Is there a oil filter adapter on the 273 that uses a gasket, like some other SB's?
There is a gasket behind the adapter plate. I replaced the original one on my brothers 273 and the old one came off in about 12 brittle pieces. Used indian head shellac on the new one and not a drop since.
 
Remove your flywheel/torque converter cover to see if the oil is coming from the back of the block. With that big of a leak on a new engine, makes me wonder if the cam plug isn’t missing.
Could you expand on your answer? This sounds like it could be something I could look into, given the amount of oil it's dumping. It made me think that a plug or gasket might be missing somewhere.
 
Could you expand on your answer? This sounds like it could be something I could look into, given the amount of oil it's dumping. It made me think that a plug or gasket might be missing somewhere.
At the dealer we would degrease the area and start the engine to see where the oil is coming from. Look for the source.
 
Oil pressure sender could have been smashed installing engine, and cracked it. One or both rear main seals could be installed backwards, intake manifold not sealed correctly could also leak, as well as a valve cover. The oil filter plate would leak onto the filter and then the ground, so should not look like a rear main seal leak. Be careful, I have seen someone install the wrong oil filter plate gasket and it did not allow the plate to fully seal, and leaked like a sieve. The proper gasket should just be a ring about 4" in dia. If the gasket includes a smaller ring at the center, do not use this one. I think it is used with an angle adapter, and not the plate.
 
Could you expand on your answer? This sounds like it could be something I could look into, given the amount of oil it's dumping. It made me think that a plug or gasket might be missing somewhere.
Cam plug? Where does that little varmint exist?
 
Auto Transport Service
Back
Top