Crankcase pressure

[tylerb]

Engine was rebuilt then sat for 2 years. The engine is now in the truck with about 2000 miles on it. I've noticed a mist of oil on the valve cover next to the breather. I currently have a breather on one side and a fill cap on the other. I was wondering how to tell if i have to much blow by or bad valve seals or if that's just normal. Was thinking about adding a tube from the oil fill cap to the air cleaner but want to make sure I dnt have a bigger problem. Took a compression test and had 150 psi +/- 5 psi on all 8 cylinders

[Steve83]

Originally Posted by tylerb

I currently have a breather on one side and a fill cap on the other.

Well, THERE's your problem. This diagram is for EFIs, but the caption describes the system as it applies to all engines:

Originally Posted by tylerb

I was wondering how to tell if i have to much blow by or bad valve seals...

A compression test:

Originally Posted by tylerb

...or if that's just normal.

No.

Originally Posted by tylerb

Was thinking about adding a tube from the oil fill cap to the air cleaner...

Don't halfass it - do it right.

Originally Posted by tylerb

...but want to make sure I dnt have a bigger problem.

If you keep driving without the PCV system, you WILL.

Originally Posted by tylerb

Took a compression test and had 150 psi +/- 5 psi on all 8 cylinders

That's not how a compression test is done or evaluated - read that caption above.

[tylerb]

So you are saying I just have to add a pcv and my problem will go away? Is there a way to tell how much crankcase pressure is to much? I can feel air coming out of valve cover when it's revved. how did I do the compression test wrong? I took out all plugs and held the throttle in while testing each cylinder. 3 cylinders went from 60-90-120-150 psi and 5 cylinders went from 90-120-150 psi. I was watching the gauge as the engine was cranked and recorded the jumps at each crank. Did this twice on all cylinders and came up with the same results

[Steve83]

You need a PCV system; not just a PCV valve. The engine originally had one, so just buy the direct-replacement parts and install them. Read the caption above for the compression test procedure.

[pete64]

The only thing "wrong" with the compression test is you did not induce some oil to see if the readings came up. That said, compression tests of this nature are highly dependent on cam timing and the state of the lifters. Your readings seem ok but you should do the ring check steve's link outlines to be sure.

That said what you are seeing is normal on a system with no PCV.

A basic carbureted system is a PCV valve installed in one valve cover and hooked up to manifold vacuum source. The other valve cover is connected to a filter in the air cleaner to filter the air that is drawn in by the PCV. You can just as easily use a filter at the valve cover but, as anyone who has done a tuneup on a stock carbureted car knows, you will still get oil out of the breather since during acceleration there is no vacuum to the PCV system.

You won't do any damage to the motor running it without a PCV as long as the valve covers are vented but you should use one if you can. Also before you hook this up make sure there is a baffle of some sort in the valve cover so you don't suck oil into the PCV.

[tylerb]

I just redid the compression test with oil and my readings came out 10 psi higher. Is that to much of an increase or am I ok

[pete64]

yes that is fine.

[tylerb]

Alright thanks for the help

[streethawk]

I put cap on the breather tube coming,from the oil fill cap...is that bad...i capped it cus it was sucking in dirt...

[pete64]

Originally Posted by streethawk

I put cap on the breather tube coming,from the oil fill cap...is that bad...i capped it cus it was sucking in dirt...

yes that is bad. You need some sort of filter there. Either get a filtered breather cap or a cap with a hose that runs up to the air cleaner.

[streethawk]

Ok 10 4 im gona get a brether filter from auto zone for 10 bucks...its only been like that for a day and havent drove much

[85turdburger]

I'm going to agree on steve with this one, A pcv system is very important on these old girls. I had the same problem with mine before I installed my pcv system. Even using filters on the breathers they were getting oil soaked without the pcv.