Does Engine oil and exhaust leak=Rebuild (please read)

[73 240Z Man]

Today I attempted to find out where my oil leak is coming from.The leak is at the rear of the oil pan but coming from where the engine meets the transmission. Does that mean it is the rear main seal? If so, can I replace it without removing the engine?

As I was diagnosing the leak, I found exhaust coming from the hose which is connected to the PCV vent (top of the valve cover). I think this means exhaust is getting past the rings and into the case and eventually . Am I correct? Does this mean I need to rebuild the engine?

Please help.

[ajmcforester]

It might be the rear seal, and yes you can leave the engine in the car.

You need to test the engine to say exhaust at that vale means bad rings. A compression test will help determine that. When did you last adjust the valves?

[steve91tt]

All engines produce some blow by (exhaust at the PCV). That's why we need crank case ventilation. How much exhaust are you seeing and under what conditions? In the end, as ajmcforester said a compression or leak down test will tell you if your rings are bad.

[Carl Beck]

I found exhaust coming from the hose which is connected to the PCV vent (top of the valve cover).

The crank case vent pipe is located on the front of the engine block, on the left side. A hose connects that vent to the PCV valve that is screwed into the balance tube between the two SU's. If your PCV valve is not operating correctly ie plugged - pressure will build up in the crank-case. This usually shows up as oil burning in the cylinders - and blue smoke coming out the tail pipe.{ and/or oil fouled spark plugs}

The vent on top the valve cover - is just that - a vent. The hose from it runs to the air cleaner. With the engine at idle speeds - pressure that can build up in the crank case should not be high enough to cause "exhaust gas" to be pushed out there.

FWIW,

Carl B.

Edited January 21, 2011 by Carl Beck

[Pop's Z]

Here's another opinion about changing the rear seal. First you should determine if the leaked product is oil or transmission lube. The engine and transmission are much easier to work on when removed as a unit. I have replaced a transmission (4spd-5spd) with the engine in the car, and it is a PITA to get them lined up correctly while lying on your back with the tranny on your chest. It's much easier to do it with the engine/tranny out of the car IMHO. It would be easier to have a partner to help, but not impossible to do yourself...just ask kenz240z.

Cheers, Mike

[73 240Z Man]

I did a compression test about a year ago or so and all the cylinders pressures were between 119-125 (if I remember correctly). The exhaust is coming from the vent on the top of the valve cover and not the crank case. It has probably been 20+ years since the valves have been adjusted. Could that be the problem? If so, how do you do it. I have some fair mechanical skills, just need info and I am sure I can do it. The crank case vent has a smaller amount of exhaust blow by coming out of it so perhaps this means the problem is with the valves?

Thanks for all the input so far. Keep it coming!

Chris

[ajmcforester]

I did a compression test about a year ago or so and all the cylinders pressures were between 119-125 (if I remember correctly). The exhaust is coming from the vent on the top of the valve cover and not the crank case. It has probably been 20+ years since the valves have been adjusted. Could that be the problem? If so, how do you do it. I have some fair mechanical skills, just need info and I am sure I can do it. The crank case vent has a smaller amount of exhaust blow by coming out of it so perhaps this means the problem is with the valves?

Thanks for all the input so far. Keep it coming!

Chris

Yes you need to adjust the valves, they are to be checked every year according to the factory service manual. If the valves to far out you can cause damage and excessive ware. Do you have a factory manual it explain well how to do this it is not hard? Take a good look at the valves while your doing this you might spot something, a bad valve guide and seals can do this also. I should have asked earlier does you car burn any oil, any blue smoke, and how much oil loss have you had?

Your compression test numbers are low, did you pull all the spark plugs before cranking the motor, it makes a big difference? Does someone have the compression range to post for him I can't exactly the range that is considered exceptionable for 73, I do remember it was over 200PSI, and was different than that of a 70-71, and 72. The good thing is the numbers look consistent. How many miles?

You could consider a leak-down test to locate seepage. Do you have an air compressor, does your compression tester have a connector to hook to a air line to it (some are made to play double duty)? Do this with the valve cover off. What you do is bring the engine to top-dead-center, or close to it, just make sure the valves are fully closed use the spark plug hole with a gauge and bring the pressure up to 100psi for one hour and see how much are was loss 90psi in one hour is called a 90%. I'm not to worried about how much it leaks, but if you can see or hear any air movement from around the valve or in the bottom of the engine. Or hear anything coming out of the exhaust or intake. This will check for leaks past the rings, and if the valve is seating properly, and sometimes catch a bad valve guide will be caught.

[Gary in NJ]

Does that mean it is the rear main seal? If so, can I replace it without removing the engine?

It's more then likely the rear seal. Not a big job but it needs to be done correctly otherwise you'll be replacing it again in short order. Do a quick search and you'll find the procedure and also understand how simple it is.

As I was diagnosing the leak, I found exhaust coming from the hose which is connected to the PCV vent (top of the valve cover). I think this means exhaust is getting past the rings and into the case and eventually . Am I correct? Does this mean I need to rebuild the engine?

As others have mentioned that is a vent, not the PVC valve. I doubt that a maladjusted valve is at all related to to this (but they should be checked and adjusted every 12,000 miles).

Are you feeling exhaust or just air coming from the vent? A good way to check is after starting a cold engine. If it is exhaust it would be warm (hot) well before the engine warms up.

With that said, I don't see how it could be exhaust. In order for it to be exhaust you'd would have a lot of blow-by from a valve. Of course, that much blow by would have an effect on combustion which would show on your cylinder pressure check. In fact, that cylinder might not even support combustion.

Regarding the cylinder pressure check, if the engine runs well don't worry too much about the value. Gauges/instruments vary as do test conditions. The FSM suggests a pressure of 171 to 185 lb/sq-in with a tolerance of 20% between cylinders. A healthy engine is within 5%. What you are looking for is a similar value for all 6 cylinders - which you have. When performing the test the engine must be warm and the throttle must be wide open.

[cozye]

Just FYI, it could be the oil pan gasket as well. It's common for the back corner of the oil pan to leak, and it will run down the front of the transmission off that back corner.

[73 240Z Man]

Regarding the pressure test, it has been a while and I am not sure of the exact numbers... I do recall them being within 15% of each other though.

As for the vent, I am pretty sure it is exhaust as it is white smoke which smells like exhaust.

Regarding the leak down test, do you do this with the cylinders dry or should I squirt some Marvels oil in there before?

Does anyone know the valve leash that is recommended? It was my dad's car to begin with and he told me today he believes it had hydrolic rockers which were swapped out for solid ones for more power. Does that sound correct? If so, does this change the valve leash setting?

Thank you again to everyone who has responded..

Chris

[Gary in NJ]

Cold:

Intake 0.0080 in (0.20mm)

Exhaust 0.010 in (0.25mm)