RebelRacer

ok guys, i got a strange problem. My engine is an '87 305, originally TPI. now has a edelbrock 650. the problem is that when i goe down the road, pressure builds in the valve covers and shoots my breather out of the hole on the passenger side valve cover, what causes this and how can i fix it?

I think i've narrowed it down to the oil baffle in the valve cover but i'm not sure.

please, i need some oppinions on this.

Kyle

Apeiron

How is your PCV valve?

RebelRacer

my pcv valve is on the driver's side, and it is fine. just the passenger side one.

Apeiron

There's vacuum at the PCV valve? Both covers are open to the crankcase, so the PCV valve should be able to vent the pressure. You could be producing more blow-by gasses than the PCV could handle though, which could indicate some sort of ring sealing problem.

RebelRacer

yea, i think i've either got a bad seal at the rings, a busted ring, or a blown head gasket. havn't decided which one i have yet, but wither way it isn't good.

Apeiron

A leakdown test would help you narrow it down.

RebelRacer

whats a leakdown test?

Apeiron

Similar to a compression test, only you blow compressed air into the cylinder and see how where and quickly it bleeds out.

RebelRacer

ok, new solution.

My problem can't be the rings, because there is absolutly no smoke coming through the exhausts, and if it wer the rings, there would be blow-by filling my entire crankcase, not just one side.

and it can't really be a head gasket either, on account of the following:

It would either run low on water, smoke, or shoot some steam out of the head area.

That leads me to believe it is inside the head. Maybe a valve seal could cause that type of problem? not sure, but tell me what you think.

thanks for the help

AlkyIROC

If you don't do a compression test and a leakdown test, any other guess as to what the problem is, is just a guess. You need to troubleshoot the problem first with known troubleshooting procedures.

The breather allows filtered air into the crankcase which is then mixed with the oil/condensation vapor from inside the crankcase and sucked back into the engine to be burnt through the PCV valve. If the PCV is plugged then it can't remove the pressure from inside the crankcase. The PCV can only pull so much air. Blowing the breather off is an indication of too much crankcase pressure. The breather is probably not stuck into the valve cover as much as the PCV and will blow off first. Once the breather is off, the excess pressure can escape and the PCV won't get blown off. If you plug the breather hole, the PCV will eventually blow off.

You won't see smoke out the tailpipe from bad rings causing excess crankcase pressure. The pressure in the cylinders is pushing past the compression rings into the crankcase so oil isn't going to get back past the oil rings into the cylinder to be burnt. air flows from high side to low side pressures.

Personally I'd say you have some broken/cracked/damaged compression rings or a plugged PCV valve. Try changing the grommet for the baffle.