Rear Main Leak - Anybody Milled the Seal Cap?

[PurpleBeeper]

I've had a really bad oil leak (1 qt./30 miles) on an engine that I revived (not run) in nearly 20 yrs. It looked like a rear main seal, so I changed it. The old seal looked pretty good though, but I changed it anyway. The engine still leaked oil like a sieve.

I pulled the trans/clutch & had my buddy prime the oil pump.... rear main seal leaking.

I read the FBBO sticky on rear main seals & bought one of those "gizmos" (fancy rear main seal cap) that is supposed to help + the top of the line gaskets. They're on the way. I plan to install it exactly as shown with calipers & 2 sets of feeler gages, etc.

I also noticed a note that said "for bad rear main leaks, sometimes milling .010" off the rear main seal cap helps by squeezing the rear main seal tighter". This got me thinking. I did have this block align honed MANY years ago & I'm not sure if they milled the rear main seal "cap" when they milled the main caps.

What do you guys think about doing this? Should I just see if this new cap works first, or go ahead an mill it .010" now? What have all of you experienced with rear main seal leaks that might help me? I did end up slightly oiling the clutch disk ($200) & I don't want to buy a 3rd one. I don't remember this engine leaking oil like this 20 yrs. ago when it was my daily driver.

THANKS FOR THE HELP

 

[62MAX]

Find a rope seal,you do not need to mill the cap.

 

[moparnation74]

Find a rope seal,you do not need to mill the cap.

X2...rope seal....knurled crank or not...

 

[fbs63]

X2...rope seal....knurled crank or not...

Milling the cap does 2 things. Most builders don't think about the second. It tightens the bottom half of the seal but it also pushes the top half of the seal away from the crank.

 

[lewtot184]

1qt in 30 miles? are you sure that the seal was installed properly? the angled lip on the seal goes to the inside of engine.

 

[RT K_line]

I would use a rope seal too if available, I haven't seen one in 30+ years. The seals on the side of the cap can also be tricky if they move or don't seat to the bottom.

 

[727]

I think Mancini has rope seals. FYI you can't install a rope seal without removing the crank first. The two piece lip seal can be installed with the crank still in place. If the engine still has the rope seal and you want to install a two piece seal without removing the crank, you're going to have to "work" to dig the old one out!

 

[khryslerkid]

FYI you can't install a rope seal without removing the crank first.

https://www.ebay.com/i/282433611363...3D711-117182-37290-0%26rvr_id%3D1389965590763

 

[727]

I stand corrected!

 

[Daves69]

Cut to fit stuff out there...........

 

[RT K_line]

View attachment 548743

https://www.ebay.com/i/282433611363?chn=ps&ul_ref=http%3A%2F%2Frover.ebay.com%2Frover%2F1%2F711-117182-37290-0%2F2%3Fmpre%3Dhttps%253A%252F%252Fwww.ebay.com%252Fi%252F282433611363%253Fchn%253Dps%26itemid%3D282433611363%26targetid%3D404696638244%26device%3Dm%26adtype%3Dpla%26googleloc%3D21164%26poi%3D%26campaignid%3D936422846%26adgroupid%3D55174491988%26rlsatarget%3Dpla-404696638244%26abcId%3D1129656%26merchantid%3D101647546%26gclid%3DEAIaIQobChMIxpqS3uuC2AIVar7tCh0BhA5TEAQYAyABEgKGHPD_BwE%26srcrot%3D711-117182-37290-0%26rvr_id%3D1389965590763

I had one of those back then. I used a screw in the oil hole to push the old one out as you turn the crank. easier with two people to do it with the rope seal.

 

[Cranky]

Yup....and anyone who has ever worked in a refinery (or anywhere pumps are used) that installed packing type sealing knows how to do it. Now a days, 99% of pumps use mechanical seals but in the 80's, 90% of them used packing or rope sealing. Mechanical seals are an EPA mandate too and imo, it was one of the few good ones.

 

[moper]

I'm curious why the rear main seal is suspect if the oil pump is turning/pumping. The rear main has nothing to do with pressurized oil. You sure it's not leaking from higher up on the block, like the oil galley plugs? Are you looking at the floor, or up into the bell housing when the oil pump is turning?

 

[tonysrt]

I had the oil pressure switch go and I thought it was the rear main. I was so relieved to find out it was oil pressure switch.

 

[moper]

In re-reading - if you have oil coming out the rear main seal when the oil system is pressurized, and you removed the flywheel and stared at the block and it's definitely not the plugs and such on the rear of the block, I can only think you have a crack somewhere. No oil galleys feed that area. the oil for the #5 main comes from the RH lifter galley to the main bearing housing. Very strange that it would have anything to do with oil pressure.

 

[727]

Have you checked the oil pressure sensor?

 

[dvw]

The only time I've ever had a BB main leak is when the holes in the retainer were located incorrectly and pushed the retainer sideways. The seal should locate the retainer, the retainer shouldn't force the seal itself left or right. Open the bolt holes in the retainer slightly. This will allow the retainer to "float" and find it's own natural position on the crank. I also don't use the side seals for the same reason. Sometimes the retainer fits tighter on one side to the block than the other. Fill the grooves with RTV. Use a putty knife to fill between the crank flange and retainer. Make sure the retainer isn't touching studs, bolts, nuts, holding the rear main cap. Make sure the 2 pan bolt bosses aren't cracked from using bolts that were too long. This will seal it.
Doug

 

[m79ded]

This is a topic that touches a nerve. I fought with a oil leak on a fresh rebuild for a month. Whatever I did it wouldn't stop leaking. I assembled countless amounts of big blocks but this was ridiculous. I went as far as welding up the crank to make it a few thou bigger, this was upon recommendation from fast fish. http://www.fastfishautoparts.com/
They were very helpful spent the time to figure it out great person to talk to. What ended up working for me was his 1 piece seal with a new Mancini retainer.

Give them a call hope you figure it out. Nothing more annoying than a oil leak.
PS. Did something change in the materials used for seals? some EPA thing? I have run into more leaks in the past few months than ever. Just wondering

 

[Daves69]

Just throwing this out there.
You might recheck the thrust fore/aft crank motion and rear main bearing clearance while in there.
Two other "outside the box" things you might rule out...
PCV and blow-by issue pressurizing the crankcase.
Slinger removed from the crank.
And then, even further out there, current knurl too sharp wearing the seal, or a reverse rotation crank with opposite knurl.

 

[Fran Blacker]

They made a number 5 main bearing to "help" remove oil pressure toward seal.

http://www.manciniracing.com/rbanlemabe.html