back pressure?

[Durwood]

I'm leaking oil from my rear main seal. I lose about a quart a week (though not all from the rear main seal, ha!). I've got a chrome open style air filter on, and I recently read that those can cause high back pressure, forcing oil out the rear main seal.

Any truth to this? And I might as well ask... What's the easiest way to change the rear main seal?

Thanks!

[CoryM]

Durwood, there is some truth to that. When ever you run an engine there is some blowby, gases from the combustion chamber that make it past the piston rings into the crankcase.
There is a lot more blowby at WOT at 5000rpm than at idle.
Just a vent is not enough to release this pressure, so out pops the weakest part, the rear main. A PCV *positive crankcase ventilation* system uses engine vacuum to help get rid of some of that blowby, thus saving your seals. If you run this engine hard definatly hook up a pcv valve/hose.
As for changing the seal it unfortionatly is a pain, have to drop oil pan, oil pump, rear crank bearing, then sorta ram the new one in.
Main thing to keep in mind is DO NOT KNICK THE CRANK JOURNAL!!!! You will be rather unhappy then.
Good Luck,
CoryM

[Zkast]

Hmmm, thinking here..... lol I cant think of one reason why a chrome breather would cause backpressure of any kind.
Little theory and reasoning for our trucks:

The PCV valve is 100% responsible for "Removing" crankcase and combustion gases. If its doing its job and there is not a huge amount of blowby you will have a neutral to negative pressure in the crankcase. IF you have excessive blowby(combustion gases getting past the rings) in the engine and the pcv valve can't keep up, it will start to "vent" from the fresh air intake breather. After time this breather will clog up from all the oil being pushed into it and cause positive pressure in the crankcase... which in turn causes the seals/gaskets to start leaking.

There are other high performance methods of pulling combuston gases from the crankcase but I think we are worried more about a stock setup here.

As for the rear main? Wait till your next oil change is due, drain the oil, pull the pan, pull the oil pump w/shaft, remove the rear main bearing cap. Here comes the tricky part and its different for every vehicle... The upper portion of the seal can be as simple as using a small screwdriver and GENTLY push on the re-enforced part of the seal, may even have to tap on it to start it moving. Once it moves go to the other side of the crank (where the seal is starting to come out) and using a pair of pliers start gently pulling the seal out, You may need to rotate the crankshaft during this process if its old and hard enough. NOTE the location and orentation of the seal lip. Felpro (the seal I would use) will show a diagram of how to install your new seal.

Once you have the seal installed and your ready to assembly again.... CHECK IT AGAIN lol. make sure your seal is in the correct grove and the lip of the seal is facing the correct way. Install the main bearing cap, torque it, install the pump and torque it. I like to use 3m weatherstip adheasive (aka gorilla snot lol) to glue the pan gasket to the block then run a small thin bead of good RTV along the gaskets and end rails. Dont use a bunch, just a small thin layer will do. When you buy your seals and gaskets, ask the parts guy for FELPRO's pan guides. these screw into the block and help you guide you pan into the correct position and hold the pan there until you can get a few bolts started. Pan gaskets will last a very long time as long as they are NOT overtightend. Start tightening the bolts until they all contact the pan, then start going around the pan, tighten each bolt until you see the gaskets just barely start to push away from the area.

phew... I need a nap now LOL

Hope this helps ya

[70shortnphat]

When useing the term" back pressure"do you mean blow by?
Or posibley crank case pressure?
When i think back pressure i think of a clogged exhaust caussing excessive back pressure.
Just trying to get clear on your question.
thanks.

[mikep]

OK I'll ask. Durwood, Do you have a breather or pcv valve on your valve covers? If not, you need one. Along with a pcv valve you also need a breather that is vented to the air cleaner on the clean side. If you just have a pcv valve on one valve cleaner and a oil filler plug on the other one then you will have blow by at higher rpm looking for someplace to escape and since at Wide Open Throttle you have no vacuum to draw anything through the PCV valve it is going to go the next easist place and that is the oil seals. Many people do not install the crank vent line to the air cleaner when they install chrome air cleaners . On a new engine with low blow by you can get away with it. On an older one forget about it. You need the breather either a stand alone one with a filter that attaches to the valve cover or one that attaches to the air claener to get clean air to the crankcase.

As a side note if you are running a high compression engine that is on the verge of detonation ( pinging) then do not use a PCV system. The oil mist in the crankcase vent gasses will agravate the condition and cause pinging and possible engine damage . I use a vented breather and a road draft tube as I am on the line compression wise even with 92 octane.

[Durwood]

I don't know what the correct term is, but in what I read the guy called it backpressure. Anyway, I've got a PCV valve and the line going to the air cleaner riser on the other valve cover. I really was just curious, is all. I was thinking it would be a whole lot simpler to switch back to a stock air cleaner than to change out the rear main seals if that was the cause.

So, here's another question then - what if I can't get the upper seal out by tapping on it? I'm not too knowledgeable about the inside of an engine; is that the end of the camshaft underneath the bearing cap? Would I have to take the camshaft out, then, in order to pry the upper seal out?

Thanks for all of your replies. I'm learnin'!

[speeddemon]

the rear main seal is on the crankshaft. You should not have a problem with pushing the top part of the seal out using a small screw driver. If the seal has been leaking for a while you also want to check to see if there is a grove in the crank. Anyway it's a Chevrolet they leak oil!