Where's it Leaking???

I'm finally back into my car after a long break. Engine guys, please HELP ME SOLVE THIS ISSUE!

440, 727 TF, TTi headers, Eddy RPM intake, cast iron heads. New rebuild that sat three years, installed and run in, rings seated. No leaks. Readjusted the rockers and put valve covers back on with new cork seals. It started leaking and got progressively worse. Oil has been gushing out the drain vent at the bottom of the trans (727TF) inspection cover. I checked around the oil pressure sender. Dry. Checked the back of the heads. Didn't notice any oil at the time. Because the motor had sat rebuilt 3 years before I fired it, some suspected the rear main seal. I replaced the cap and seal with a Mancini billet unit with Viton seal, added a hemi pan and pick up with a windage tray/seal and filled her up. Leaks just as bad. The last time I started it, the headers smoked and I found that the valve cover bolts were a little loose. Noticed a drip on the driver's side headers. Tightened them and not thinking they could be the cause, I pull the transmission to check the cam plug. The plug is dry as a bone. DAMMIT. The upper part of the bell housing is dry. The TQ converter doesn't look like it's slinging oil. It's not dripping at all the crank flange is dry as well. Zero drips. Looking at the bell housing-to-engine mating surfaces, both are absolutely oily from the starter height down and the starter too is very oily. SO. I get the light waaaaay back there and yep. There's oil dripping off the back of the heads. It was indeed leaking at the valve cover gaskets and onto the headers. This and the oil on the starter is becoming my red flag.

For those experienced in chasing this issue, tell me. Under engine pressure, can oil leak out the back of the valve covers and sneak down the back of the block and enter the bell housing via the starter hole? It seems far fetched, but I am out of guesses. I just never suspected that all that oil could drip down the block and get past the mating surface of the trans. It's a lot of oil. I mean, 5 minutes and there's a half quart and it's leaking like a sieve out the inspection cover. And it's on both sides. My big mistake was not running the engine after I tightened the valve covers. The engine runs like stink. No bog at all. Roasts the tires in a blink, so I eliminated a head gasket leak, but who knows? Please entertain me with your thoughts. I want to nail this BEFORE the trans goes back in. Valve cover leak, or???

Go to Harbor freight. Buy a $6 regulator. Plug the dipstick tube and breather. hole. Set the regulator to 5 psi and air up the engine. You may see the oil being forced out right away. If not spray it with soapy water and look for bubbles. It's fool proof to find leaks.
Doug



https://www.harborfreight.com/air-t...regulator-kit-with-dial-gauge-68223.html

Thanks Doug. Doing a "leak down test" was something I had given a thought to last night as I was looking for the culprit. I have a regulator on my compressor. Not sure how accurate it is, but I could crank it way down and give it a go. Where best should I air up the engine? Great tip!

You could use either valve cover. I never use cork gaskets, they eventually shrink then need retightened. To me their garbage.

I’ve not used rubber ones. Might give them a try. I’m going to get to that test!

UPDATE: I couldn’t get bubbles but could hear air coming from the seal area. I boosted the pressure to 10-15 lbs. air is blowing out the right side of the rear main seal. Not the left, just the right, which makes me wonder if it is the seal halves leaking where they meet.

Advice?

I used cometic’s on hemi I had, never leaked and reusable. Pricey, but worth it.

What kind of valve covers? If they stamped steel they may have dimples on the sealing surface from over tightening. If they're MP cast aluminum covers then maybe they're hitting the intake runners and not seating properly? I know this is a problem on small blocks where those covers don't sit flat when using aftermarket intakes. They lips that hit the intake runners need to be ground for clearance.

It's got to be the covers not sitting properly. Since it's happening on both sides and in the same locations. Makes sense considering the motor is probably leaning a couple degrees toward the rear as well.

Guys read my update. The valve covers are Holley aluminum. I’m gonna replace the valve cover seals too. I’ll look up the better seals. I don’t know if compressing 15 lbs of air is a good test but it’s DEFINITELY blowing out one side of the main seal.

Why not check ur blow by with a meter.

I've never used 15 psi. But I can tell you that a rear main that's good won't leak at 5 psi.
Doug

I've always had issues sealing up factory heads with a stiff valve cover. The factory head castings are typically not consistent around the sealing surface of the valve cover. With a stamped valve cover that flexes, the valve cover will bend and seal, even in the low spots where the head castings aren't perfectly flat. Stiff machined valve covers don't flex, so no matter how tight the bolts are there's going to be a variance of pressure applied to the VC gasket and oil usually pushes its way out in those spots. When I went to a modern aftermarket aluminum head, the sealing surfaces are spot on, and they sealed up much better with a variety of valve cover types.

the last two "bleeders" i've messed with were the back corner of the passenger side valve cover. a friend of mine has a 383 4spd car and oil was covering the tranny and exhaust. we actually took the gear box out a couple of times to re-seal it. in a final act of desperation i checked the valve cover bolts and the back corner bolt on the passenger side was loose. tightened it up and bingo no leak. i had a nuisance leak on the 440 in my '65 coronet. nothing serious but suspected it was coming from the back of the oil pan. i was planning to yank the engine and fix it but in the last final act of desperation i tightened up the passenger side valve cover; leak gone. sometimes the leak is never where you suspect it.

if it were me, I would put some oil dye in it and hit it with a black light. I have done this before and the leaks lights up like a Christmas tree, LOL

https://www.amazon.com/Interdynamic...eak+uv+dye&qid=1653655360&sr=8-2


Joe

I could feel air coming out at 5 lbs just faintly. Was trying to get the soap up in there and it was difficult. Boosted the pressure and it clearly blew air from the passenger side of the crank flange. Definitely eliminates the cam seal and threaded plugs from possible issues, so I think I’ll button the trans back up, replace the VC gaskets and run it once more just to be sure they aren’t the easy fix.

I love this forum. Never lets me down. That’s a great idea Joe. Thank you.

Lee tot and Bigdaddy, thank you. I’m going to replace the gaskets before I touch the main seal and see if you guys are geniuses. LOL. After yanking the trans, I would be totally okay if you’re correct.

i think a lot of times people blame the rear seal when it's something else. i don't know how many rear seals i've done thru the years but have never lost one (hope i didn't jinx myself here,.. ).

For sure. I did a complete rebuild of a 440-6 for a guy forty years ago. He put the engine in the car himself and called a couple days later to tell me the rear seal was leaking. He brought it to me. It was pouring oil off the back of the engine. I dropped the pan, looked at the area around the seal and realized it wasn't leaking. He had a mechanical oil pressure gauge in the car and he had failed to tighten the nut on the tube. Hard lesson learned.

Me and a buddy chased oil leaks on his car for months. Turned out it had a Vac-U-Pan, and for whatever reason, it was pressurizing the crankcase. I can't explain that. Took that stuff off and everything was fine.