Is my rear main leaking or no ?

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   Oil can leak from the intake manifold, run down the backside of the block, and look like a crankshaft seal leak.
It's very difficult to successfully replace the crankshaft seal in-chassis. Oil tends to get where you don't want it and interferes with the sealing. Even a perfect job with the engine on a stand will still leak a drop or two when the engine is shut off. They always leak a little. That bell housing inspection plate is always a little wet. 

All engine gaskets and seals dislike crankcase pressure. Proper working PCV helps. The crankcase should not pressurize unless the oil filler cap that serves for the air inlet for the PCV is clogged. 

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FSJunkie Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4602	Post Options Post Reply Quote FSJunkie Report Post Thanks(0) Quote Reply Posted: Mar/26/2023 at 12:56am
	Oil can leak from the intake manifold, run down the backside of the block, and look like a crankshaft seal leak. It's very difficult to successfully replace the crankshaft seal in-chassis. Oil tends to get where you don't want it and interferes with the sealing. Even a perfect job with the engine on a stand will still leak a drop or two when the engine is shut off. They always leak a little. That bell housing inspection plate is always a little wet. All engine gaskets and seals dislike crankcase pressure. Proper working PCV helps. The crankcase should not pressurize unless the oil filler cap that serves for the air inlet for the PCV is clogged.
	'66 Marlin '72 Wagoneer '73 Ambassador '77 Hornet '82 Concord D/L '84 Eagle Limited

Candymancan Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Feb/21/2023 Location: Virginia Status: Offline Points: 90	Post Options Post Reply Quote Candymancan Report Post Thanks(0) Quote Reply Posted: Mar/26/2023 at 10:14am
	Nothibg is clogged already checked.. but the oil filler cap has no vacuum line to the air cleaner anymore it just sits open. Ny thread in 2017 i made asked why ny rear main leaked after i did that. Seems my edlebrock air cleaner didnt come with the nipple for the cleaner to hook ul the hose to it so i left it open. Im going to get one today and a vacuum line for it and see if that doesnt anything. But its weird.. doesnt the pcv work better at higher rpm ?? So i wonder if no vacuum line to the carb air cleaner, so it can pull air from the oil filler is the cause. Maybe the open air cap isnt enough ? I dunno man im just tired of this leak. Im not sure. Just throwing theories out here. Because i remembered this was the start of the leak when i swapped that stock system out. But i forgot if it was coincedence, or why i kept the edelbrock air cleaner in if it was or not. It isnt the intake or valve covers. I used a bore scope to look back there. All i see is a small coolant leak on the drivers side bolt which ive known about. I did discover two loose transmission bolts back there though.. So loose they worked themselvs out fairly far on top of the back of the engine and the washer wobbles which is weird... Its easier to test this open oil filler cap theory than dropping the stupid pan a 3rd time.. so i guess well see.. it makes no sense though as wouldnt the pcv be pulling air through it at high rpm ??, its a weird coincidence when it started in 2017 after i just happened to remove the factory air cleaner/oil filler vent tube. and all the vacuum lines to the engine minus the pcv. And Charcoal canister stuff. If the pcv pulls air through the oil tube.. why did factory put a vacuun line to the air cleaner ?? I think maybe ill get a new pcv valve.. eveb though mine is super clean and rattles and works. I can even hear it at idle in the cab rattling Edited by Candymancan - Mar/26/2023 at 10:31am

jcisworthy Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jul/23/2009 Location: North Carolina Status: Offline Points: 2768	Post Options Post Reply Quote jcisworthy Report Post Thanks(0) Quote Reply Posted: Mar/26/2023 at 11:33am
	If it leaks a PCV or hose from the oil filler to air filter will not fix it I run these engines on the dyno without either hooked up and no leaks unless something is wrong Not a bad thing to hook it up but do not expect it to fix the problem I have seen unused accessory bolt holes leak before. There are a couple threaded holes that come close to the outer head bolt and with one factory and one Indy head oil leaked from under the valve cover through the threads and down the engine Something to check anyway
	Specializing in dyno services, engine building, and cylinder head porting rbjracing.com Phone Number 518-915-3203

Buzzman72 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/15/2009 Location: Southern IN Status: Offline Points: 2562	Post Options Post Reply Quote Buzzman72 Report Post Thanks(0) Quote Reply Posted: Mar/26/2023 at 1:24pm
	A properly operating PCV valve only opens at a "medium" engine vacuum. At low vacuum, the weight of the plunger keeps the plunger on its seat. At high vacuum, the plunger [theoretically] seals against the TOP side of the valve housing. The cap at the oil filler tube [formerly known as the "breather cap"] allows atmospheric air into the crankcase, but also can vent excessive crankcase pressure to the air filter housing, when operating properly. If your piston rings [or broken ring lands] are allowing excessive blow-by, and an insufficient amount of the pressure is being released, the crankcase pressure CAN blow oil out the rear main seal. It can also blow out the RTV if it's used on the intake manifold end seals. Because piston rings have end gaps, no cylinder is going to seal perfectly. So there will always be a percentage of blow-by. It's simply the nature of the beast. If you're really wanting to do a thorough diagnosis, buy, borrow, or rent a cylinder leakdown gauge. Assuming you have access to a compressed air source, it can show you if a particular cylinder [or several] has/have a blow-by problem. [It will also show leaking valves, but those won't cause excessive crankcase pressure.] Doing diligent diagnosis can save you from simply throwing parts at a problem.
	Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.

Candymancan Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Feb/21/2023 Location: Virginia Status: Offline Points: 90	Post Options Post Reply Quote Candymancan Report Post Thanks(0) Quote Reply Posted: Mar/27/2023 at 2:16am
	Question. The amc crank where the seal rides. Mine has a polish on it sligjtly where the knurles are those //// lines could this be the reason ? The knurles are so long too but the seal only sits in the front.. So there must be more to this. Are there double lip seals or offset seals that would work ? You know a seal that rides on the fresh knurles and not the one with the groove polished into it ? Wouldnt the 4.0 or perhaps the chrysler 360 rear main which is douboe lipped fit ? They do look similar

Trader Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 5689	Post Options Post Reply Quote Trader Report Post Thanks(0) Quote Reply Posted: Mar/27/2023 at 10:58am
	A long shot but have seen what your describing once on a Jeep. What happened is someone put so much RTV in the rear main seal faces that it came off as a bead and pretty much blocked off the oil return on the back of #5 bearing cap. Enough oil would flow at idle to relieve the back of the bearing, but at higher RPM's the passage was so blocked off that oil just poured out the back of the rear main seal as it had no were else to go. Just a long shot as stated.

Candymancan Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Feb/21/2023 Location: Virginia Status: Offline Points: 90	Post Options Post Reply Quote Candymancan Report Post Thanks(0) Quote Reply Posted: Mar/27/2023 at 11:54am
	Oh i gwt it. I didnt put enough on for that. It didnt even squish out. Thats why i was worried it migjta been the pan ( hense why i smooshed it with a socket exntention and hammer haha.. No i made sure it wouldnt block that drain.. It didnt even squish out the side of the pan anywhere else either. The pan must (float) and not be 100% flush to the metal surfaces. The rear rubber lips pop out way too much too which means it must float in the back si the rtv couldnt actually squish unless you used a BOAT load. Which i didnt exactly do. I made it asd thick as the rubber would be. (To fit in the groove and stick out just enough) it still leaked like this though even with the cork and rubber. Litterally each time i do this.. it leaks exactly the same as prior its weird. Its why im wondering if the worn out knurles is the cause. My crank does have 150k on it. Theyre still there.. but on some spots they are not as all i see if a smoothed line from the original seal. In fact i dont think my original seal is original. Its yellow on the outside which i think is an older style fel pro ? Which means its done prior even before me maybe Are there double lips seals like the 4.0s have ? Or off set seals. Would a 4.0s seal fit on a 360 ? They look identical with the tans and everything. Minus one being double lip (the 4.2 and 4.0) and one being aingle for the 360. I have a 4.0 seal and it actually even fits in the bearing cap too when i put it in. To test Edited by Candymancan - Mar/27/2023 at 11:58am

BigRedCornhead Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Mar/13/2008 Location: Nebraska Status: Offline Points: 92	Post Options Post Reply Quote BigRedCornhead Report Post Thanks(0) Quote Reply Posted: Mar/30/2023 at 12:53pm
	my money is still on the cam plug, what has everyone used to stop that from occurring, im positive during my rebuild i put something on the threads still weeps a bit?