need opinions

[80widelarado]

Okay so awhile back I replaced my front crank seal on my 360, at the same time I did the timing chain also (it needed it bad). Well fast forward about two months and now my rear main seal is just dumping oil to the tune of about a quart a week. It also puffs smoke out the tail pipe when I fire it up. So my question is do I even bother with a new rear main seal or do I just wait and give it a full rebuild? What would you guys do? Back ground is it's a 1980 cherokee with the original 360 in it and around 240000 miles.

[Tatsadasayago]

Sounds like your engine is just plain tired. You gotta keep in mind that when the AMC V-8 was designed, 60k miles was considered End Of Life territory.
As far as your symptoms; it sounds like your rings aren't sealing well which is causing 'Blow By' which is combustion pressure leaking past the rings and pressurizing the crank case...which overwhelms the PCV and causes seals and gaskets to start leaking.
Smoking on startup sounds like your valve guides and seals are worn out allowing oil to leak into the combustion chamber after shutdown.

Sounds like you have a 'Wednesday Engine' if it's still running at 240k!

If you have the engine rebuilt by a competent builder and good machinist, you won't be sorry! A fresh 360 is a ton of fun when you're used to a worn out mill.

Jim

[FSJ Guy]

If it's not knocking due to worn bearings, I'd throw a rear main seal in it and see what happens. As mentioned above, oil on startup is likely due to worn valve guides and seals. IMHO, not the end of the world. A RMS is less than $10, but a major PITA to install unless your Y pipe DOES NOT have to be moved to get to it. Some do, some don't. If your Y pipe goes right underneath the rear of the oil pan, you'll probably have to remove it. That's the PITA part. The rest isn't too bad, just messy.

[haminawag]

Odd that a main seal would just spontaneously start gushing oil, worn main seals will leak like hell if you have a plugged PCV valve or crankcase breather. Also, are you sure the leak isn't coming from your oil pan gasket? Seems like a coincidence since you just had the oil pan off to do the front seal.

[80widelarado]

We actually didn't take the pan off to do the front seal. It doesn't knock or even tick at all just pours oil out of the rear main, with the occasional puff when I start it. Honestly I'm very proud to say that it's 34 years old and still on the factory motor that's never been rebuilt. I'm just worried that every time I replace a seal it's going to blow out another one.

[Gumby]

If you are that worried about bustin out seals, I would just run it until you can get it rebuilt properly then run it for the other 240K.

[80widelarado]

I've just been told by my automotive instructor at college that it will more than likely just blow another one. Hopefully I'll be able to pack it soon and actually work on it rather than using it as my daily plus 9 mpg sucks in a daily lol.

[Stuka]

Why would it blow a new seal out? The only reason it would is if the engine has a lot of blow by and the crank case ventilation is not working.


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[80widelarado]

Why would it blow a new seal out? The only reason it would is if the engine has a lot of blow by and the crank case ventilation is not working.


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Stuka I was told that if the rings are bad then the compression that is escaping out of the cylinders is looking for a place to go. That's why when I fixed one leak another one just got worse. So following that logic if I fix the next leak it will just find another weak spot to come out. I'm worried that next time it might be a head gasket that fails dead lining my wonderful Jeep.

[haminawag]

Why would it blow a new seal out? The only reason it would is if the engine has a lot of blow by and the crank case ventilation is not working.


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Stuka I was told that if the rings are bad then the compression that is escaping out of the cylinders is looking for a place to go. That's why when I fixed one leak another one just got worse. So following that logic if I fix the next leak it will just find another weak spot to come out. I'm worried that next time it might be a head gasket that fails dead lining my wonderful Jeep.

But Stuka is right, and it's why I mentioned the crankcase breather being plugged. If there is a lot of blowby the excess crankcase pressure will find the easiest way to escape to atmosphere, and the easiest way is through either a crankcase breather vent, or through the PCV valve or both. But if there is no way for the crankcase pressure to escape (Plugged PCV or crankcase breather) then a seal may gush oil, but not if the pressure can escape easily. If your engine is SO worn that the blowby gasses are pressurizing the crankcase even with a clean PCV valve and breather then it's time to retire that engine for sure, and I'd be amazed that it'd even run.

Make sure it has 5 qts. of oil in it, pull the breather cap off, fire it up, and have a look underneath (Safely) is it pouring oil? It shouldn't be, unless the rear seal is missing in action. Can you feel a lot of pressure escaping through the breather pipe?

[80widelarado]

It actually runs great I drive it 50 miles every day. But I will do what you advised and see what it does. If it's not pouring oil out would it be ok to replace the rear seal? I just want to keep it on the road through this winter as it's my only 4 wheel drive. After that I'll be able to park it and pull the motor to rebuild it.

[Blazer3664]

Make sure it has 5 qts. of oil in it, pull the breather cap off, fire it up, and have a look underneath (Safely) is it pouring oil? It shouldn't be, unless the rear seal is missing in action. Can you feel a lot of pressure escaping through the breather pipe?

This ^^^^

Stuka wrote:Why would it blow a new seal out? The only reason it would is if the engine has a lot of blow by and the crank case ventilation is not working.


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Stuka I was told that if the rings are bad then the compression that is escaping out of the cylinders is looking for a place to go. That's why when I fixed one leak another one just got worse. So following that logic if I fix the next leak it will just find another weak spot to come out. I'm worried that next time it might be a head gasket that fails dead lining my wonderful Jeep.

You do realize, you and Stuka are talking about the same thing?

I was told that if the rings are bad then the compression that is escaping out of the cylinders is looking for a place to go.

This is what everyone is referring to when they say blow by.

Taking the breather cap off the oil fill tube, as Haminawag mentioned, is one way to find out if thats a contributing factor with your oil leaks. If there is a lot of blow by, taking the breather cap off will give it a "path of almost no resistance". That should stop, or at least drastically slow your rear main seal if blow by is whats causing it.

All engines have some amount of blow by, nature of the beast. New, prime condition engines it will be so minimal as to be "almost" nothing, but with the right tools it is measurably there, however minute.
The more wear, the worse it will get.

This is why they have crank case breathers and PCV systems.

If these systems are plugged it will not allow the blow by to escape.
If the blow by is excessive it will be more than they can handle.

In either situation the crank case is then pressurized and will find a place to "leak" that pressure out.




Hope that helps explain things a little better.


Jim

[Blazer3664]

Two other small things..............

Dont leave the breather off as a "fix". Its a filter to keep junk OUT of you engine, just like your air filter.
It wont hurt anything by taking it off and testing as above, but dont drive it that way.


As far as rebuilding a 360, IMO, get another one (pretty common and not too $$) and do one of 2 things............
1) if your engine will be alright for a while, rebuild the other one as finances and time allow.
This will let you still drive until its ready. Two guys (that know what they are doing) can swap an engine, from running to running again, in a couple hours or less. Not even a bad weekend job for a couple shade tree guys.

or 2)if your engine is just plane worn out, get a decent runner. Swap it in and drive while you rebuild your 360, then do the last part of #1

Jim

[Tatsadasayago]

Sometimes life has you in a situation where you gotta be creative with vehicles. If your test show noticeable blow by out of the filler tube when you throttle the engine you have some choices.
1) You can drive very gently, keeping the RPMs down and feed the old girl a steady supply of oil. (Cheapest Solution)

2)You can clear/clean the filler vent filter/cap and PCV which are likely plugged or restricted. (Kinda Cheap)

3)You can do 1 and 2 and replace the rear main seal. (Cheap enough but changing the rear main is no picnic)

I was forced by divorce and low paying employment to keep driving my 78 Chief after the 401 grenaded so I traded a pistol for a 304 powered Hornet and swapped the engine into the Cherokee. It was T I R E D but it ran, which was very important at the time.
It had the same blow-by issues yours appears to and I did all 3 things to keep it alive.
When it came time to relocate to Sacramento for a new job I loaded up a case of 30 weight oil, put in new filler and PCV valve and drove the almost 500 miles from eastern Nevada checking the oil level every 100 miles or less.

Toward the end of that drive she was starting to burn blue on hills under power, when coasting down the other side and leaking enough to coat the rear window and gate with a layer of oil splatters. I recall I had 2 or 3 cans of oil left when I arrived.

If you keep on top of things your engine may last much longer than you might think despite the problems. Oh, and by all means do as Blazer suggested: Get busy on a replacement engine so yer not stuck without a winter rig.
Wishing you the best!

Jim

[80widelarado]

Luckily being an automotive student at the local college I have access to lifts, lots of tools and extra help. So come monday I'm going to talk to the instructor about replacing my rear main seal sometime very soon. Also I never drive the jeep hard because I know it's old and tired. Slow pulling off lights and 60 mph on the highway. Honestly I have no doubts if I keep oil in it and treat it nice that it will last she has never left me stranded yet. (knock on wood) Also thanks everyone for the advice on keeping her on the road.

[carnuck]

The hose for the PCV gets filled up with goop too.