Cylinder 5 oil leak

[vp277]

Hi Corvair gurus. I bought my first Corvair few months ago, it's a 65 with 140 engine, have been sorting it out. I fixed a bunch of engine and transmission/differential oil leaks, but one remains and it puzzles me. I have oil dripping of the cooling fins of cylinder #5 where it joins the head, I circled that spot in red. The top of the engine is dry. All other bottom oil leaks have been fixed. The compression is uniform among all 6 cylinders. Where could that oil be leaking from?

[66vairguy]

One problem with air cooled engine oil leaks is the fan blows a lot of air over the head and cylinders so oil gets "pushed around". Finding the source can be difficult on a dirty engine.

I'll guess it's a push rod "O" ring seal.

Judging by the mangled push rod tube in the picture, somebody has already changed them by crudely using a pair of pliers/channel locks to remove them! Folks make tools to get the push rod tubes loose with out damaging them. If the ends the seals go on are bent, then they WILL leak.

You have to pull the valve rockers off and remove the push rods. There is also a seal under the push rod stud/head nut that goes on the head stud to hold the head on. It can also leak.

The old "O" rings were neoprene and leaked after a couple of years. Now Viton seals are used that last much longer.

[vp277]

I took those pictures in the dark with a flush, the engine looks dirtier than it is. It's s crusty, but I degreased it, I can't see any leaks out of pushrod tube seals. I had that engine sit for a couple of weeks and oil kept sipping from that one area of the fins. Could it be a tiny crack in the head?

[flat6_musik]

That's a bit of a busy area. You've got the crankcase ventilation pipe coming out above that area (with its own O-ring) and I believe that the dipstick isn't far away either. That's why it's essential that your PCV system is functional and (doing all it can to) maintaining a slight vacuum in the crankcase to help with oil leaks. Engines with worn rings and extra blowby problems can overwhelm the stock PCV setup.

[vp277]

Good call on PCV related leaks, my guess was that the leak originates where the PCV tube enters the block. I did have an issue with excessive crankcase pressure, that was fixed. The oil dipstick tube is dry, PCV tube is dry on the outside. There's no oil leaks on top of the engine, just on the bottom of the cooling fins of cylinder #5. Is there any way for engine oil to sip between the head and the cylinder?

[66vairguy]

Good call on PCV related leaks, my guess was that the leak originates where the PCV tube enters the block. I did have an issue with excessive crankcase pressure, that was fixed. The oil dipstick tube is dry, PCV tube is dry on the outside. There's no oil leaks on top of the engine, just on the bottom of the cooling fins of cylinder #5. Is there any way for engine oil to sip between the head and the cylinder?

This is a long shot ----- You mentioned "could the head be cracked", and is there a way for oil to leak between the head and cylinder. In an indirect way YES. The lower head studs (just above the pushrod tubes) go through the head into the oil sprayed rocker box of the head. The rocker stud/socket screws onto the head stud, but UNDER it is an "O" ring to prevent oil leaking. Oil might be leaking past the "O" ring down the head stud hole in the head and would drip down at the area were the cylinder meats the head. I suspect oil leaking into the head stud hole would accumulate a bit so it keeps weeping even after the engine is turned off.

As I said --- a long shot. You'd have to clean the area with a spray solvent, carefully, to observe. Some use a spray powder (deodorant or foot power) on a suspect area to see were the oil is traveling from. I've never done it, but it may work if you don't mind cleaning up the powder mess.

[66vairguy]

That's a bit of a busy area. You've got the crankcase ventilation pipe coming out above that area (with its own O-ring) and I believe that the dipstick isn't far away either. That's why it's essential that your PCV system is functional and (doing all it can to) maintaining a slight vacuum in the crankcase to help with oil leaks. Engines with worn rings and extra blowby problems can overwhelm the stock PCV setup.

There should NEVER be a slight vacuum in the crankcase via the PCV system. If there is, then the PCV system is NOT working correctly.
See viewtopic.php?t=18023

[vp277]

Thanks, i'll investigate the possibility of the rocker stud oring leaking.

[flat6_musik]

That's a bit of a busy area. You've got the crankcase ventilation pipe coming out above that area (with its own O-ring) and I believe that the dipstick isn't far away either. That's why it's essential that your PCV system is functional and (doing all it can to) maintaining a slight vacuum in the crankcase to help with oil leaks. Engines with worn rings and extra blowby problems can overwhelm the stock PCV setup.

There should NEVER be a slight vacuum in the crankcase via the PCV system. If there is, then the PCV system is NOT working correctly.

I didn't see where it says that.

[vp277]

The leak is fixed! it was due to improperly torqued rocker studs. Thanks to all for your help.

[66vairguy]

The leak is fixed! it was due to improperly torqued rocker studs. Thanks to all for your help.

Glad it's fixed. Sounds like it was oil getting past the rocker stud "O" ring. Now they are replaced with the Viton type.

BTW --- over the years the head torque value has changed in the shop manuals. The folks that have done a lot of Corvair engine work decided 30 fl lbs. (clean threads) was the ideal value to work well and prevent head studs being pulled out of the block. It's what I've used and have had no issues with pull studs or leaking head gaskets.