BeachinVette

What do you guy's think bad pcv valve or worn out heads?? The car does smoke a little when started.I did not have this problem till I put on a Holley Dominator intake.. I can`t see how that would have anything to do it. But...

Thanks
Bob

rjs82vette

Had the same problem on a 400 small block in my 76 Blazer.... the oil passages on the back half of the head were clogged by gunk.....so instead of the oil being drained into the oil pan it was setting in the heads....pooling up and getting sucked into the pvc valve.... Smoked like a trian........ just went in with a airhose and use compressed air to blow out the drain holes...... then I changed the oil...... Blow by would be cuase by the oil coming up with no where to go....

8T1-7T9 BIONIC VETTE

I have this problem too....I'll be watching this thread for a solution.... :seeya Cappy

Noel Carboni

"Major blowby" is a sign of exhaust gases getting into the crankcase. Not usually a good sign. Is it blowing your dipstick up out of the tube sometimes?

Things that could cause blowby are worn rings, a broken piston, a broken ring, a blown head gasket, various cracks in the heads or block, worn out exhaust valve guides/seals, ... you get the idea. None of these are good things.

Many people don't realize that good sealing of the bottom end of the engine relies on the PCV valve drawing a vacuum inside the engine. This causes the front and rear seals to draw tight against the crank, and the negative pressure tends to keep oil from running out of places like the valve cover gaskets and oil pan gaskets. When the blowby exceeds the ability of the PCV to evacuate the crankcase you'll start seeing leaks.

Did it happen all at once? Are you seeing the engine run hotter than it used to? If so, you probably have piston or ring problems. Been there, broke that. Check:
http://home.att.net/~ncarboni/BrokenPiston.html

-Noel


[Modified by Noel Carboni, 5:16 PM 2/26/2002]

flynhi

I read somewhere that this can also be caused by excessive crankcase pressure that accompanies a 383 buildup. Any comments on that?

The Dude

Hypereutectic pistons, perhaps?

I'd look at doing a compression test as the first order of business. That will rule out (or confirm) Major Badness right away.

Noel Carboni

I can't see why there should be "excessive crankcase pressure" with any particular engine displacement, save for the possibility that with a custom engine build the piston/ring clearances were set particularly large, allowing cylinder pressure to sneak around the pistons.

Note that nothing seals perfectly, and some engine builders even design in a certain [small] amount of blowby to "clear the oil" off the oil rings.

-Noel

gkull

Leak down testing is a good way to measure what Noel went over. Leak down testing is measured in %. Anywell built motor will have very minor leak down no matter what the cubic inches after ring breakin. As miles go up and the rings and bore ware this leak down % goes up. If you have ever had preignition or detonation you can actually break the upper piston lands and rings. Which results in major blow by.

If I had oil above a small amount of mist. I would have a leak down test done. Motors are not like the human body they don't heal on their own! :seeya

A very simple test is: Pull the PVC out of the valve cover and if you feel pressure coming out of the hole with the motor running it's not a good sign. I have never had a oil return plug up so I can't comment on that. I also don't know why it would start right after and intake change

Wrencher

You mentioned that it started when you changed manifolds. I'd make sure that the PCV is getting full manifold vacuum first, i.e. that it is hooked up to the right port. it has to really suck! Usually directly under the carb or in the main plenum of the intake. If you want to check for excessive blow-by, pull the PCV out of the valve cover (but leave it hooked up), remove the oil filler cap or air cleaner hose from the other side and run it (warn engine!). If it smokes like a train (sort of a whiteish mist), cylinder pressure (hence "blow-by") is getting past the rings. It will smoke a little even with a good engine, so I'm talking about a substantial amount of smoke, especially when you rev it up. I did a Bubba fix on a guy's truck once that involved running the hose that normally went the air filter out the back of the engine, creating a road draft tube. It kept the filter from oiling up. Good luck.

Hans

Hans


[Modified by Wrencher, 11:52 AM 2/26/2002]


[Modified by Wrencher, 11:53 AM 2/26/2002]