Something I was told about the rear main seal leaking?

[Notplayn]

I was told by a tech that the reason the rear main seals leak so bad in the GNs is because of the valve cover breathers that are installed. Can anyone second that or is it bs????

 

[Boost231]

bs

complete and TOTAL BS

 

[BlackMetal]

I've never heard that. I know it's popular to change out the factory breathers, but I've never heard of that in relation to the rear main leaking. The rear main leaks because it's a crappy rope seal.

 

[cruzn57]

Well..................

I think a little of both, and more.
rope seal is not the ultimate, but alot of neopreme seals leak too!
the breather story has some truth to it, but , in my opinion, when you make boost ( which we all do often) there is pressure getting past the rings, and into the crankcase, ( how else does your oil get so dirty?) which has to vent some where, the PCV works with vacumn, but not boost, so under pressure ( boost) the escaping gasses must exit somewhere, and, as this ain't no balloon, it will push out at the easiest exit, it could be the rear seal, could be pan gasket, etc, etc
thats my story, and you can form your own theory......

cruzn57

 

[Gary Wells]

I think a little of both, and more.
rope seal is not the ultimate, but alot of neopreme seals leak too!
the breather story has some truth to it, but , in my opinion, when you make boost ( which we all do often) there is pressure getting past the rings, and into the crankcase, ( how else does your oil get so dirty?) which has to vent some where, the PCV works with vacumn, but not boost, so under pressure ( boost) the escaping gasses must exit somewhere, and, as this ain't no balloon, it will push out at the easiest exit, it could be the rear seal, could be pan gasket, etc, etc thats my story, and you can form your own theory...... cruzn57

--------------------------------
As what cruzn57 says, except they all leak, some worse than others, depends on how often, to what extent, and how long that you go into/stay into boost. Even a new replacement rubber hi-tec one will leak in time, but will last longer than the factory rope seal one.

 

[2QUIK6]

Crank case pressure should vent thru the breather on the valve covers. If you still have the breather tube going to the turbo inlet, the pressure will easily go there, otherwise most people remove that and have 2 breathers, one on each valve cover..more than enough to releive any pressure in the case. The rear seal is in a groove and would be extremely difficult to get pushed out, the pan gasket woudl go way before the rear main.
If you have that much blow by that the breathers aren't doing there job, you got other serious problems to deal with than just a seal leak.

The original rope seal gets compressed over time and simply does not seal very well over time. Same is true for the neopreme seal, it just keeps its elasticity longer and lasts longer.

 

[VadersV6]

I would bet most of the leaky rear seal guys have leaky PCV valves that dont seal shut all the way under boost, and/or they never clean their breathers, and the elements are all packed with oil, keeping the engine from breathing. Completely eliminating the PCV system altogether is stupid IMO. PCV systems shouldnt be considered smog equipment. They should be considered necessary equipment.

 

[bison]

I would bet most of the leaky rear seal guys have leaky PCV valves that dont seal shut all the way under boost, and/or they never clean their breathers, and the elements are all packed with oil, keeping the engine from breathing. Completely eliminating the PCV system altogether is stupid IMO. PCV systems shouldnt be considered smog equipment. They should be considered necessary equipment.

Yes another reason to get rid of the PCV. Leaking in boost and sucking oil in. If there isnt adequate breathers on the top of the engine it will leak everywhere form the pressure build up inside. BS on the breathers causing leaks. Sometimes the 2 breathers arent enough if the engine has a lot of blowby and will still sweat a little if beat on.

 

[VadersV6]

Yes another reason to get rid of the PCV. Leaking in boost and sucking oil in. If there isnt adequate breathers on the top of the engine it will leak everywhere form the pressure build up inside. BS on the breathers causing leaks. Sometimes the 2 breathers arent enough if the engine has a lot of blowby and will still sweat a little if beat on.

Go to your local high school and take a semester of auto shop.
#1-Blowby isnt pressure. Its oil/gas vapor. If your crankcase has so much pressure in it that you need massive breathers to keep it down, your engine has MAJOR problems. The PCV system sucks this stuff up and recirculates it and reburns it. It also will put a small vacuum in the crankcase (if the breathers arent huge), which helps keep rings seated and the ring grooves clean. Reburning blowby is better than letting it loosely float around in your crankcase. This burnt oil vapor is acidic and is bad for...you guessed it...seals, and especially soft metals, like bearing metal. If you add a good catchcan to this system, now the backs of your intake valves will start cleaning themselves. (assuming you dont have an alky kit that does it for you) Some valves have so much carbon buildup on the backs of the intake valves that it reduces the relative valve lift like .100-.200". (Ive seen .300-.400" thick carbon deposits on the backs of some intake valves)... It does serious damage to port flow. Also, the catchcan/pcv system will retain the crankcase vacuum, and at the same time stop the vapor from recycling into the cylinders....oil vapor is like nitro for inducing detonation/pre-ignition.
Improved emissions was a by-product of PCV systems. They provide a useful purpose which helps the engine last longer and keeps everything cleaner. The idea is that you use a quality AC PCV valve which doesnt leak boost into the crankcase. Add a catchcan and your engine will thank you in the long run. Also keep the breathers clean. If you retain the PCV, and add a catchcan, you will also see the benefit of the breathers not eventually getting saturated with oil/gas vapor. They dont "sweat" from pressure. They sweat when the vapor is kept unchecked, it condensates and builds up on the breathers. Now the breathers cant "breathe", and the PCV cant suck up the vapors because now there is no air moving through the block.

 

[Pronto]

Pontiac rope seals are notorious for leaking and they see no boost. They are just a poor design.

 

[TurboMonte 2]

BS-BS! NO WAY a rear main seal (even in relatively poor condition) would represent the path of least resistance for blow-by/ whatever crankcase pressure. This stuff will head out thru the breather--and would be even better if there were multiple breathers,,,

 

[cruzn57]

you really think your rings seal that good?

all motors have blow by, ALL MOTORS!, when new, you may have as much as 3-5 % leakage past the rings, after you beat it a while, as much as 10% leakage! (more than that, and your needing help)
where do you think that goes? past the rings into the crank case. every revolution puts more into the pan, from each piston,( like 231 cubic inches of blow by each revolution) under boost , your PCV doesn't work!! duh, no vacumn! so the only vent you have is breathers, or, any other weak link, ( like a rear main seal, or gasket, or?)
can your breathers pass 231 cu in of blow by each rev? think about it, the bottom of each piston goes up and down just like the top does!( yea I know some pistons are going up when others are going down), the air on top the piston goes out the exhaust, where does the blow by go?
why do you think nascar and drag cars run a pan evac system? could it possibly be the breathers can't handle that much blow by?
I am trying to point out that there are other thoughts on this.

thanks
cruzn57

 

[Pronto]

all motors have blow by, ALL MOTORS!, when new, you may have as much as 3-5 % leakage past the rings, after you beat it a while, as much as 10% leakage! (more than that, and your needing help)
where do you think that goes? past the rings into the crank case. every revolution puts more into the pan, from each piston,( like 231 cubic inches of blow by each revolution) under boost , your PCV doesn't work!! duh, no vacumn! so the only vent you have is breathers, or, any other weak link, ( like a rear main seal, or gasket, or?)
can your breathers pass 231 cu in of blow by each rev? think about it, the bottom of each piston goes up and down just like the top does!( yea I know some pistons are going up when others are going down), the air on top the piston goes out the exhaust, where does the blow by go?
why do you think nascar and drag cars run a pan evac system? could it possibly be the breathers can't handle that much blow by?
I am trying to point out that there are other thoughts on this.

thanks
cruzn57

I don't think anyone is disputing the fact of blowby. I'm not sure the assesment of 231 cu in of blowby in block is viable though. The block below the pistons is an open area unlike a cylinder which is pretty much a sealed volume. The "compression" in the crankcase would be comparably lower from the volume of the block and oil pan. Race engines run looser than a street engine for less friction so naturally they will have more blowby and oil consumption and no PCV. If I'm not mistaken the system they use is a vc cap that has a hose going down to the headers to draw vacuum on the vc. I've only seen 1 one each side and they are virtually the same size as the single vc vent on our engines. So if 2 of them is good enough for a 500+ CI loose race engine why wouldn't 1.5 breathers be good enough for evacuating a 231 street engine (in decent shape)? Now if the engine was suffering from bad rings then the pressure under boost would be substantially higher. If the rings are bad then most likely the gaskets and rope seal is bad and likely to leak. So if you have a fresh engine (least blowby) theoreticly a rope seal shouldn't leak with proper venting but in actuality they leak.

 

[wagon]

Here's my take on it. The breathers don't cause the leaks, but they don't help in preventing them. Under vacuum, a properly functioning PCV system is going to apply a little vacuum to the crankcase which should prevent good seals from weaping. (It obviously won't stop a major leak, though) Now, when the car is under boost, it is going to have blow by, without a PCV system to apply vacuum to the crankcase. The factory system also applys vacuum to the crankcase by way of the breather in the valve cover that draws vacuum into the inlet of the turbo. So, the PCV system will help prevent seals from weaping under vacuum, and the factory breather system will prevent it under boost. That is how I see it. That is why on my stocker, I am going to keep it in place. I am thinking about putting one of those catch cans on the factory VC vent and see how that works at keeping oil out of the turbo.

 

[441120]

Rocket science

Don't forget that under boost the car is accelerating, and while the car is accelerating where is the oil in the pan going? That's right, up the back of the pan and block to the rear main seal!
So now the block is somewhat pressureized, PCV is inactive due to boost, all the oil is sloshed up against the back of the pan on to a spinning crankshaft with a two piece rear main seal, it's going to leak somewhat.
Any blow-by gasses in the crankcase that need to vent must travel from the pan to the valve covers, with everything moving and oil trying to return to the pan, pressure will build in the pan, it might be small but it's more than atmosphere. Add a little pressure to a two piece seal under oil and want it leak free? Must be a GM engineer

 

[TURBOTERRORV6]

Don't forget that under boost the car is accelerating, and while the car is accelerating where is the oil in the pan going? That's right, up the back of the pan and block to the rear main seal!
So now the block is somewhat pressureized, PCV is inactive due to boost, all the oil is sloshed up against the back of the pan on to a spinning crankshaft with a two piece rear main seal, it's going to leak somewhat.
Any blow-by gasses in the crankcase that need to vent must travel from the pan to the valve covers, with everything moving and oil trying to return to the pan, pressure will build in the pan, it might be small but it's more than atmosphere. Add a little pressure to a two piece seal under oil and want it leak free? Must be a GM engineer

so what is the solution to the weak 2 main seal? do venders sell a more stronger main seals 4 the rear? thanks

 

[441120]

Unless someone invents a one piece seal set up for a 20 year old engine... SOL
The best you can hope for is a neoprene seal with the parting line offset. Pack the main cap side grooves with the packing strips in the rope seal kit. Then use a good sealer at the contact surfaces,(not too much ) hope you're having a lucky day, put it together, let it cure. Put oil in it, road test it, then don't look because sooner or later you'll see a little spot, a drip, a speck. Don't worry that's not an oil leak, just sweat from all that horsepower

 

[bison]

Go to your local high school and take a semester of auto shop.
#1-Blowby isnt pressure. Its oil/gas vapor. If your crankcase has so much pressure in it that you need massive breathers to keep it down, your engine has MAJOR problems. The PCV system sucks this stuff up and recirculates it and reburns it. It also will put a small vacuum in the crankcase (if the breathers arent huge), which helps keep rings seated and the ring grooves clean. Reburning blowby is better than letting it loosely float around in your crankcase. This burnt oil vapor is acidic and is bad for...you guessed it...seals, and especially soft metals, like bearing metal. If you add a good catchcan to this system, now the backs of your intake valves will start cleaning themselves. (assuming you dont have an alky kit that does it for you) Some valves have so much carbon buildup on the backs of the intake valves that it reduces the relative valve lift like .100-.200". (Ive seen .300-.400" thick carbon deposits on the backs of some intake valves)... It does serious damage to port flow. Also, the catchcan/pcv system will retain the crankcase vacuum, and at the same time stop the vapor from recycling into the cylinders....oil vapor is like nitro for inducing detonation/pre-ignition.
Improved emissions was a by-product of PCV systems. They provide a useful purpose which helps the engine last longer and keeps everything cleaner. The idea is that you use a quality AC PCV valve which doesnt leak boost into the crankcase. Add a catchcan and your engine will thank you in the long run. Also keep the breathers clean. If you retain the PCV, and add a catchcan, you will also see the benefit of the breathers not eventually getting saturated with oil/gas vapor. They dont "sweat" from pressure. They sweat when the vapor is kept unchecked, it condensates and builds up on the breathers. Now the breathers cant "breathe", and the PCV cant suck up the vapors because now there is no air moving through the block.

If PCV is important than why dont all race cars run one? If your breathers are too small you will get a pressure build up of blowby in the crankcase. The PCV can not handle the volume of blowby that occurs at WOT. I doesnt even function at WOT. A vacuum pump would be a more effective scavenger at WOT. I dont want any hot oily vapors sucked into the intake risking detonation the next time i nail it on an engine i have $8000 invested in. Anyone who is serious about engine longevity will be changing their oil so frequently that it doesnt get a chance to become acidic or polluted with fuel. I change mine after one weekend or thrashing. Oil is so cheap theres no reason not to do it. For nearly stock boost levels the AC PCV with a positive check is all thats needed, but for a 25-30psi engine with heads and turbo its not the way to go. Yes i do run a lot of alky and that itself pollutes the oil. The last one i dissasembled with over 30k miles and 4 years of 25-30psi boost had no PCV and the entire intake and all combustion chambers were nearly spotless. 99% of the time i had only 93 octane in the car. I didnt observe any detonation not running a PCV.It must also be noted that oil consumption was almost nothing also. For a daily driven TR a PCV should be functioning, but for the hardcore buildup that gets driven hard once or twice a week it will cause more problems than its worth. The PCV will help in an emissions test by leaning the mixture a little through the vacumm leak it is.