Opinions

[panmarcum]

Had my spare head rebuilt with new cam and rockers,decked, valve seals, guides were well within parameters as per machine shop. Since i plan to keep my325is for a long time had my friend more experienced shop owner is changing the head in his shop (foreign car specialist) while I am on a ship in the gulf of Alaska. Found oil in all cylinders and he asked me how much oil I was burning which is about 1/2 a quart every 1500 miles. Car ran fine no smoking only had worn cam lobes on #6 with unadjustable eccentrics. 150,000 miles. Since the oil is in all cylinders equally do you all think it is brittle valve seals? Sorry for the long post.

[E30_fiend]

Could be valve seals or a head gasket. Possibly even cracked or worn valve guides.


Taylor

[jeffnhiscars]

Bad valve seals will allow oil out not in.

[jlevie]

Bad valve seals will allow oil out not in.

Huh?

Bad valve seals will cause oil to be sucked into the cylinders on the intake valves.

[E30_fiend]

Huh?

Bad valve seals will cause oil to be sucked into the cylinders on the intake valves.

This.

[panmarcum]

Thanks guys your ideas is what I kind of suspected. In with a reman head with new bmw head bolts and head gasket. All new radiator and heater hoses,flow matched and cleaned injectors, throttle body warmup plate gasket with 3 new screws, timing belt and tensioner, new thermostat

[jeffnhiscars]

Huh?

Bad valve seals will cause oil to be sucked into the cylinders on the intake valves.

This.

I was picturing bad blowby pushing it out. I stand corrected :oops:

......or aliens may have hacked my computer and posted that when I was out

[SkiFree]

If you have the chance (and haven't already), don't forget to check the rocker shafts as well.

[dnguyen1963]

I was picturing bad blowby pushing it out. I stand corrected :oops:

......or aliens may have hacked my computer and posted that when I was out

Air enters the engine when the cylinder head creates vacuum and bad intake valve seals will allow oil to enter as well. Aliens have definitely taken over your computer...give everything up now.

[jeffnhiscars]

Huh?

Bad valve seals will cause oil to be sucked into the cylinders on the intake valves.

I've given this some thought and here's my question...

...if oil can be sucked in past worn intake seals why can't blow by from badly worn rings be pushed out past the exhaust seals ? Seems to me to be the exact same laws of physics.

[jlevie]

Normally the crank case of the engine (and area under the valve cover) will be at less than atmospheric pressure on an M20 engine. Flow past worn seals on the exhaust valves will mostly be from the cylinders to the valve cover as most of the time the exhaust valve is open the pressure in the cylinder will be above atmospheric. But there is a brief period during valve overlap where that can change.

Seals are necessary for the exhaust valves a) to prevent pulling exhaust gases into the engine and b) prevent oil from running down the valve stems.

[jeffnhiscars]

Normally the crank case of the engine (and area under the valve cover) will be at less than atmospheric pressure on an M20 engine. Flow past worn seals on the exhaust valves will mostly be from the cylinders to the valve cover as most of the time the exhaust valve is open the pressure in the cylinder will be above atmospheric.

We are almost saying the same thing.

This would be why we used to pull the oil filler cap off the valve cover looking for blue smoke as another way to check for blow by. Since you seem to agree that flow past the exhaust seals is possible (you say as much), then wouldnt such an instance in an engine with worn rings push blow by oil (albeit in vapor form) out the exhaust seal as part of that "flow" ?

[jlevie]

Seems to me that if there was enough blow by to put the crank case pressure high enough for there to be flow past the exhaust seals, there'd be gobs of oil vapor entering the intake via the breather hose. What might leak past the exhaust seals would be insignificant compared to what was going into the intake.

[jeffnhiscars]

I dont think its crankcase pressure resulting from blow by that's behind my reasoning (or lack of reasoning) since pressure doesnt create blue smoke, combustion does..except in compression combustion engines but thats another story.

If a piston can suck oil past the seal of an open intake valve which is the clear path of least resistance then it can surely push it in the opposite direction past an open exhaust valve seal IF oil is present on the cylinder side. True there is ALWAYS oil under the valve cover to draw in if the seals are bad, but my point is based on significant blow by being a source of oil that can get pushed past the exhaust guide seals at the same time blue smoke is being pushed out the tail pipe. Hence blue smoke under the valve cover.

I read all that in a fortune cookie so it must be true

[jlevie]

If a piston can suck oil past the seal of an open intake valve which is the clear path of least resistance then it can surely push it in the opposite direction past an open exhaust valve seal IF oil is present on the cylinder side.

That is certainly a true statement. But if there is oil in the cylinder (or oil smoke) after that cylinder fires, there's a much bigger problem.