Engine is a 78 302 (306) , 11:1 compression. Only have breathers on the valve covers, no PCV. After 3 hours of run time, the rear main went out. Pulled everything apart, new rear main seal, 1/2 hour run time, rear main leaking again !!!! Losing my mind here. Any ideas ? Do I need the PCV, aren't the breathers enough ? Thanks for your input.
Please elaborate, I don't quite understand. I'm Talking about the rear (main cap) engine seal . Thanks for the response.
So its the old style lip seal in the bearing cap? Not much that can make them leak when new. So long as they are installed correctly. Crankshaft end play should be checked. Crankcase pressure can be an issue if your filters are old and plugged up or you have a lot of blow-by. I'm a firm believer in PCV valves.
Yep, 2 piece, can't understand it. Unless the end play is the issue. The first one I took out had minimal damage to the seal (only at the bottom), left some residue on the crank however. Wasn't installed dry. All the filters are new. Heck everything is new. Don't think blow by is an issue. If I pull the breathers out of the valve covers, smoke (steam ?) rolls out of both. If I pull the oil dipstick, smoke (steam ?) rolls out of there too. I'm at a loss !
OK, I know its a 78 block but for some strange reason did it have a rope seal in it stock? if so then you need to look at the cap where the seal sits and look if there is a small spike there to hold the rope seal from moving. Just a thought. Second are you sure the seal is installed correctly? should look like this. Other than that check to see if you have a galley plug leaking or the flywheel bolts are leaking. Good luck on this one, sometimes it can be hard to figure out just what is leaking.
Oil gallery plugs can be a nightmare. We have quite a few Hemis at work that leak at the rear gallery plugs. Tough to find. You can use dye if you have access to a black light. Thats what we do at work.
. how much oil pressure do you have? 80 psi and above can blow a seal. i had a high pressure pump one time and had same problem, went to stock pump never blew another seal.
Sounds like a crankcase pressure issue to me, are the breathers the open type like a k n filter or just the ones with the holes in the bottom. It may not even help to install pcv if you have a lot of crankase pressure. You really need to do a leakdown test not a compression test to see whats going on in the engine, if rings did not seat good you will have issues like you have. Do you have smoke or vapor coming out the breathers, does your oil dipstick push up after spirited driving ? I have been fighting similar issues to what you are going through but with leaky valve covers.
You might also make sure the leak isn't coming from the oil pan gasket, I had this problem with mine. I put a 9 quart pan when I swapped the 331 in and had leaks both front and back. I ended up dropping a quart from the pan to solve the leaks. The rear leak looked exactly like it was coming from the rear main. Just me, but I run a PCV system on all my motors. The tiny bit of blowby that gets sucked into the cylinders really doesn't make a hill of beans worth of difference in the performance
Thanks for all the replies guys. I'll be pulling the engine again this coming weekend. This thing has been a nightmare ! Started with multiple tranny issues, now the rear main issue. Guess I'll install a PCV, currently has vents on each valve cover (not open element type,just holes in the bottom). Not sure on the oil pressure I'll have to check that. Can't remember if it's a high volume pump or not. I'll re-do the seal and drop a quart or so out of the 7 quart pan. Oil pan gasket seems to be fine. First rear seal had a very small piece missing on the very bottom (not sure what that's about). It's not the old style "spike" type, the galley plugs seemed dry, and the flexplate bolts aren't leaking. Only things I can think of right off hand is the type of Permetex I used isn't the "curing" type it stays flexible, and the other is that the flexplate was impacted on instead of torque wrenched. Will know more when I pull it.
Def. get some kind of pcv setup.There has to be something there to help draw the vapor/gases and pressure out of the crank case.Without some kind of set-up,the pressure is going to go to the weakest link:the rear seal,intake front/rear runners,or the timing seal.I have seen some that have actually blown out the press in galley plugs!I've always used permatex blue or red rtv on the cap ends with no problems.As for using an impact on the flywheel bolts,thats how I've always done mine,without any problems.Cheap little electric impact from Autozone.
I just had an oil consumption issue, and found it to be the pcv system. I put fabricated valve covers on, and did not baffle the pcv valve, and it sucked copious amounts of oil through the carb. Did not even smoke. I made a baffle from some sheet metal and it solved the issue. You should really have a pcv system. Can really help with over pressure in the crankcase.
I agree with the PCV system being necessary but I doubt it is causing your leak. With two piece seals you need a little (very little) sealant on the ends and as with all seals you need to lubricate them before instalation. It takes long enough for oil to get to the seal that the rubber will burn away on the sealing lip. Vaseline or assembly lube will save the seal. Before installing a new seal look at the crankshaft surface. If it has a series of diagonal lines on it the I would use a rope seal (soaked in motor oil before installed).
