Crankcase pressure; oil pool in valve cover

CDeutsch · 03-07-2005

Ever since I swapped a set of stock cams back into my 7 bolt 2.4 with stock 2G head I've been having problems keeping oil in the engine. First time out it blow out the cam end cap (where the cam angle sensor goes on other year cars). Then I replaced it with a new cap and blow it out again. Now the cap is holding (for a quick 10 minute cruize at 15 psi boost anyway) but oil is still pooling in the valve cover. It's probably coming threw the oil cap but the gasket is fairly new. I have both the PCV and the barb that goes to the intake both venting threw a fuel filter and then to a plastic bottle. I don't end up with a lot of oil in the fuel filter or bottle which is odd. Also I did a compression test and it's a little high. It's up 30psi since I initially did it a couple 100 miles after the rebuild to 230, 225, 225, 230. (Compression is 9:1)

I'm going to check the timing next, but even if it was off would it cause compression or crankcase pressure to go up? I'm running out of ideas. This car is about one incident shy of the auction block.

On a side note, I learned that you can't just throw any old cams in an engine without degreeing and expect a power increase. With the crowers I was running I was limited by knock to running about 15-18 psi. Now I've run way over 20 with the stock cams.

john · 03-10-2005

I would guess your compression is a larger factor in only being able to run 18psi but... I would guess the oil pool has to do with a crack in the valve cover. If you tighten it too much, it will crack very easliy. The spec is only about 3/ft#s. Check the oil cap gasket again and make sure it is rubber instead of plastic. That is all I can think of now.

**JET** · 03-10-2005

Hey Chris, is the bottle that you dump the breather hose into open on the top so it can vent? I am sure you know this since you have been around for a while, but it doesn't hurt to ask

Could it be possible that a valve seal fell off when you were changing cams? You didn't take the retainers off at all, did you? Who machined the head? Sounds like it maybe be a bad machine job if it was rebuilt recently.

CDeutsch · 03-10-2005

Thanks for the ideas guys. I'm leaning toward the timing being off. With the Crower cams I had in for over 6000 miles I didn't have this problem and the only thing I changed when it started happening was swapping the Crowers for some stock cams. I'm almost positive the cam marks are lined up (relative to each other) but I'm second guessing wether the crank could be off a tooth. I've had the valve cover off two times since the problem started and the most recent time I used all new gaskets. It's not really a slow leak, it's forcefully coming out (it blow out the end cam twice). Plus I don't know what else would cause the compression to be so high. I can't seem to find anybody with compression in that range. I'm going to check the timing this weekend and I'll let you guys know what I find.

Raptor · 03-10-2005

The crankcase pressure is probably directly a result of the much higher compression which probably is caused by the cam timing as you guessed. Cam timing doesn't effect static compression at all, but has a significant effect on dynamic compression. Degreening the cams will likely help all the issues you are having.

CDeutsch · 03-16-2005

Well my timing marks are dead on. Damn, I was hoping for something simple but like Raptor said it's the cam timing. After looking into it apparently the closing of the intake valves is one of the variables that affects dynamic compression. So the 30-40psi jump in compression came from when I went from non-degreed Crower Stage 2's, back to stock 2G cams because the stock cams close the intake valves a lot sooner.

Also I was crunching some numbers this weekend and I don't like the results. I should have been more careful when buying pistons (at least I'm learning a lot):
http://www.rosspistons.com/calculator.php

Here's the numbers I used.
Bore: 3.426
Stoke: 3.937
Head: 46
Gasket: .045
Deck Height: .015
Dish: -13
Num Cyl: 4

The one big number I don't know is the Deck Height. And the Head and Gasket numbers are rough estimates but should be close. With those numbers I get a static CR of 9.75.

I really want lower compression because I'd like to run pump gas and more boost. My options for lowering the compression (without swapping pistons) are:
1) Adjustable cam gears to tweak when the intake valves close.
2) Radical cams to keep the intake valves open longer.
3) Thicker head gasket.
4) Modify the head to create a bigger compustion chamber
5) Sell the damn thing to someone who wants to run mostly race gas.

Any advice? I would replace the pistons if I could do it without removing the crank. It's a 7 bolt and it seems to be holding so I don't want to F' with it. Anybody had luck doing that? I feel like that is just asking for trouble.

Raptor · 03-16-2005

The less obvious answer may be the best on this, opening up the combustion chamber might net you a bit more power overall as well, the factory does a horible job of making the chambers equal and correctly located, they are quite a bit off on every head I have checked. The valves are also pretty well shrowded. You could probably cure all these problems in one shot ast well as cleaning up potential hot spots etc. Not the easiest answer, but probably the best overall for improving things.

At-Least-It's-An-Evo · 03-16-2005

Your only good options are to increase the combustion chamber volume or get different pistons. You would have been fine with that dish cc on a 2.0l motor. A really thick headgasket wouldn't be good for squish, which would make the car more likely to knock than a car with the same overall compression ratio, but with the correct pistons. The Cometic and Mitsu metal headgaskets that most of us run are already a bit on the thick side. I don't know how metal you can remove from the combustion chambers without ruining the quench areas.

Raptor · 03-16-2005

There is quite a bit, expecially considering it is a 2.4 block, the combustion chaber is designed for a smaller bore so opening it up even to the 87MM (@.020") is going to help, they actually are already under 85MM as well so there is room even on a 2.0 to open them up some without touching the quench area.

**scheides** · 03-16-2005

how thick of a Headgasket can you put on there? If you put in one that is like .12" into that formula, you'll be down to 8.5:1 CR.

I know the VW guys put pretty thick headgaskets on their vr6 motors to drop the CR & turn up the boost, but I don't know how thick. I think they drop the CR from 10.1:1 to 9.0:1, roughly 1 full point (depending on the specific app). more info here

CDeutsch · 03-19-2005

Quote:

Originally Posted by scheides

how thick of a Headgasket can you put on there? If you put in one that is like .12" into that formula, you'll be down to 8.5:1 CR.

I know the VW guys put pretty thick headgaskets on their vr6 motors to drop the CR & turn up the boost, but I don't know how thick. I think they drop the CR from 10.1:1 to 9.0:1, roughly 1 full point (depending on the specific app). more info here

I don't think anyone makes a headgasket that thick for a 4G64. The largest I've found so far is like .079. And like NonTurboSpoolinGuest said large gaps between the heads and the pistons can be bad. The ideal quench height is like .040.