1973 340 supposedly rebuilt years ago, then sat for years before too many miles put on it, (maybe 10-12k). I got it going, it had a bent pushrod, had to rebuild carb, replace all tune-up parts, etc. I drove it for about 4,xxx without any problems. It runs strong, oil pressure cold is 60+, drops to around 40 going down the road warm, only has 10-15 at idle but comes up quick with a little more rpm. Hadn't used oil or leaked at all for 3-4,xxx miles, then I opened the hood one day and WHOAH!, oil everywhere! I thought bad PCV or breather so I replaced them both, had a mechanic replace the intake gasket (looked like where it was leaking) and thought all was cool. Checked under the hood a few days later, and oil everywhere again! I thought the gasket wasn't holding but on closer examination the oil is coming out of the dipstick tube. You can hold it about 3,000 rpms without the stick in it and it will start blowing little drops of oil out. I thought I had blown something up but it still doesn't have any blowby smoke and runs as strong as ever.
Any advise for this old bodyman? (Sorry if I've overlooked the obvious but I am NOT a mechanic.)
TIA,
Dallas

head gasket

The engine runs good and doesn't misfire. I put in a new PCV valve and replaced the breather in the other valve cover, both are aftermarket, not OEM, though. The breather has a hose that goes to the air cleaner (aftermarket air cleaner). When I got it I checked the compression, it was decent at that time but I havent checked it since I've had the oil problem. I'll take it to a mechanic and have a leakdown test done.
Thanks for the help.
Dallas

Does it have the MP valve covers on it. I've had quite a few sets that didnt breathe well. Get on it hard and they'd push oil out the dipstick. Put stock ones on and fixed it.

first things first. DEGREASE THE ENGINE

then run it and look for the wet spot. then we can help. too many reasons without a starting place

generally "blowing Oil" is caused from too much crank case pressure.

Does it have a PCV valve and a breather? If either were plugged, that may cause it.........

Sounds like poor or failed crankcase ventilation, to me. Clean it off and make sure the breather is in tip top shape and not too restrictive. The pcv should be on one valve cover, with a breather diagonal to it on the other.

I have picked up cars with motors like this several times and fixed it with an improved ventialtion system.

Check compression, though. It bent the pushrod earlier in its life for a reason, unless you fixed that too.

Agreed, While the engine is running pull the PCV hose off the carb. Engine RPM should increase or possibly kill the engine. Put hose back on and start engine again. This time disconnect the hose at the PCV valve. Engine should do the same thing. I guess the PCV hose could also be collapsing. Double check the entire PCV system. If all is good you have ring problems. Maybe just take it out and
Rings could be gummed up and letting a lot of blowby by.

Ok, I'll try to be more clear on some of the details, starting from my last post, and 70dart360's question.
Original valve covers. I replaced the breather and PCV with parts store items, not OEM parts.
I degreased the engine several times thinking it was the intake gasket, before determining I could hold a piece of cardboard behind the dipstick tube with the stick out, hold the engine about 3000 rpms for a couple of minutes and get oil droplets on the cardboard, coming out of the dipstick tube.
PCV valve is in driver side valve cover, breather is in passenger side with a hose going to the bottom of the aftermarket air cleaner.
When I first got it, it had a miss. I did a compression check then, that's when I discovered the bent pushrod. I have no clue why it was bent. I can't remember the compression #s now but it was pretty even for all cylinders after I replaced the pushrod.
I'll have to check if the PCV hose is collapsing.
You can take the breather and PCV out and hold the engine at 3000 rpms and it doesn't appear to have any blowby.
I've cleaned the motor off and ripped it up and down the road a few times and it will still be clean. Drive it 5 miles at a steady speed and there will be oil all over the front of the motor and under the hood.
I'll have a mechanic do a leakdown test and go from there.
Maybe I need to install a taller tube and longer dipstick out of a later model. LOL, just kidding.
Thanks for everyone's replies. I'll try to post again when I find out the results of the leakdown test.
Dallas

heres something to check.

my old 340 used to coat the front dipstick area with oil after a high rpm run. anything about 6000 would do it easily. I would clean the motor, run around at relativily low rpms and id see nothing. make a blast up to 7000 and id see oil.

turns out I had broken 1 or 2 pistons right at the edges and was getting bad blowby. the blowby was coming out of the vent hole on the feule pump (theres a small vent hole on them near the top).

might want to check compression again and see if you have the same issue.

but another check to see if the pvc is working is to remove the breather and put a stiff piece of paper over the valve cover grommet. it should be sucked down onto the cover. if not, you have a restriction somewhere or really low vacuum.

The hose should go to the base of the carb not the air cleaner sounds like vacuum problem after listen to the other posts.let us know for sure the problem after you get it fixed Good luck

I had this exact same problem with a 318 I used to have. Nothing I did to the crancase venting/PCV system stopped the blow by, and the engine ran great. I ended up taking it apart and re-honing the cylinder walls. I guess I didn't do a good enough job when I initially put it together, as the problem was solved after doing this.

Ring Seal.... Have the leakdown done. If it's over 6-8%, you have ring sealing issues.