Compression check...

[Hozer 88GTConv]

Okay, I've had it.

Number 5 holds steady for over an hour with 175 psi dry.
All others are between 165 and 180. To me, that's good. Certainly not bad enough to explain my oil loss. So where then?

I am consuming one quart of oil every 200 miles and fouling number 5 totally within a few minutes of operation. I've changed valve seals twice, checked valve seats when I r/r'd the heads a month ago, and the intake manifold gaskets have been changed 5 times. It NEVER smokes.

The plug in number 5 is soaked on all the threads and the electrode tip. Even fouls a plug two heat ranges hotter.

This is pissing me off. Oil ring? Would it hold pressure that long with a bad oil ring?

I'm thinking of swapping intakes, b/c the valves have a lot of oil on 'em and the plug condition still makes me think it's coming from "up top"...

I am days away from pulling my engine if I can't figure this out (again). I've pulled the heads twice now in three months.

[PKRWUD]

What do you mean it "holds steady at 175 for over an hour"? Brand new engines leak down at least 5%. How are you determining this? Have you done a leak down test? That will tell you where the oil is coming from.

[Hozer 88GTConv]

PKRWUD,
Thanks for your reply. With an Actron gauge and a warm engine (i.e. running for over an hour and a brief 10 minute cool down) the left bank 5, 6, 7, 8 all read between 165 and 180 PSI.

I re-read number 5, and it held steady at 175 for nearly an hour. I had the valve covers and the upper intake manifold off in an attempt to locate escaping air. No joy.

This is driving me nuts.

[mustangII460]

. The best info on comp checking.

[Hozer 88GTConv]

Thanks for the link, outstanding site.
Cheers...

[Rev]

They won't let me delete this post? Who knows why? Only can I edit it? Dumb?

Rev

[Rev]

Originally posted by PKRWUD
What do you mean it "holds steady at 175 for over an hour"? Brand new engines leak down at least 5%. How are you determining this? Have you done a leak down test? That will tell you where the oil is coming from.

I, too, am wondering about the "leak down test" and how you did it?

Rfev

[Jeff Chambers]

'Course its gonna hold steady. A compression gauge has a one-way valve on it. Once the compression enters the gauge it's kept from exiting (basically a Schrader valve in there). The gauge hold till the cows come home, but the cylinder's a different monster. Do a leak-down. Anything more than a few % warm will be a good indicator of where that oil's going.

[TMASTER]

I heard that when the 5.0 motors from ford when they were new, were only 155psi on the cylinders. I did mine last year and they were all at 150psi. 153Kmiles on the block.

The oil loss could come from 5 different places:
1. Piston rings are shot
2. Sucking it from the valley from the lower intake gaskets not sealed.
3. valve seals are shot
4. Its leaking out of the motor, especially more when you drive.
5. Sucking oil from the PVC valve, or breather tube going to TB.

[TMASTER]

if its only cylinder #5, its got to be the valve seal or sucking it from #5 runner from the intake. pretty rare for jsut one cylinder ring to be bad out of the whole motor.

Check your roller rockers and make sure they are set right!!!, is the car running bad or smooth?

[Hozer 88GTConv]

I have changed seals twice now. The full-metal jacket type to be sure on number 5.
Total head rebuild done two months ago. Fel-pro Gasket is tight, new ARP studs with sealant, bronze guides and plates were perfect. Valve setup is money. Car runs very strong. Until, number 5 fouls then it is barely noticeable by an occassional miss. MSD and a plug two ranges make fouling harder.
As soon as this is done, i'm getting a Kenne Bell. I swear.
No leaks at all, all plugs look perfect except 5.

You are right on the one-way check valve. Dammit. That makes me want to buy beers for everyone who bothered to post and slam my head in a door jamb for being so retarded.

This has gotten the better of me.

I have rebuilt the heads, seals, lapped the valves etc. But number 5 is sucking oil and my gut is telling me the lower intake /head surface is bad.

I just don't want it to be rings, b/c the bottom end is less than 20k from a full rebuild from a very reputable race shop.

Shit, I 'm just going to get a new TFS intake and try it out.

Beers for everyone, on me....

[TMASTER]

Consentrate on number 5 cylinder only, Its got to be the piston ring, sucking the oil from intake gastket, or the valve seals.
Do the compression check on that cylinder, get a different compression tester, open the TB and turn the key and let it crank 3 times then check the pressure.
last resorts, pull the cylinder head off and you will find the problem. compression check, those numbers were way too high that you said. I hope its not the piston ring, if you havent changed the oil, you can check the oil pan for metal Good luck, let me know what happens.
PS: I used RTV gasket maker on my lower intake felpro gaskets together on both sides. Ive had a car that sucked oil from runners, i didnt want it to happen again lol, but i doubt thats your problem now.

[Hozer 88GTConv]

I am going to do it again today.

Following dry/wet procedures to the "t".

compression check, those numbers were way too high that you said.

I have TRW flat top pistons with small valve reliefs and TFS heads. That's why my numbers are what they are.

I'll post in an hour or so with the complete dry/wet numbers...thanks again.

[TMASTER]

You might as well check the 5 6 7 and 8 cylinders, check each cylinder 3 times, and write down the numbers for them, all the cylinders should be pretty equal, i havent checked a motor yet that they were really different from eachother, ( good luck i guess)
if number 5 is any less from the others tell me how much

[PKRWUD]

There is a fairly easy way to tell if you have a leak at the intake to head gasket.

1) Hook up a vacuum gauge to the intake manifold.
2) Fully close the throttle plate by backing out the idle screw all the way.
3) Plug up the PCV valve opening.
4) Disconnect and plug any vacuum hoses attached directly to the intake manifold.
5) Disconnect the wire to the positive side of the coil.
6) Crank the engine and observe the vacuum gauge. From 3" to 7" of vacuum (at a minimum of 250 cranking rpm) is normal. A defective intake manifold gasket, or warped surface, will give, in most cases, a zero reading.

[skiwesser]

I have the exact same problem on #2 (plug always wet with oil, fouls, ocasionly backfires on hard shifts) but good compression all around, although the rings are worn by wet/dry test.
I now belive it's sucking oil between intake & head as i home gasket matched both and proably went to far on intake.
I'd like to try the test PKRWUD suggested but I don't fully understand:
Hook vac. guage to intake where?

[PKRWUD]

Hook it to any vacuum port on the intake, and then plug up the rest of them.

[backn9sec]

Speaking of compression,

I check the compression after every race and mine has been running between 160 & 170 pretty much.

This last time all cylinders were showing the same numbers but #1.

It showed 195! (cold) I checked it a day later (cold) same thing.

I can't think of good reason why this has happened. Maybe someone here can explain this.

It's probably something simple.

sorry, didn't mean to hijack this thread

tom

[Hozer 88GTConv]

Here are all 4 from the left bank in order. 5,6,7, and 8.

I'm doing the comp check now with an actron gauge.
Cranking it 5 times, TB blocked WOT.

I'll post in 20 mins with the dry numbers, then the wet.

Note the number 5 plug is a 3926, not a 3924 like the others. That's the only way I can keep it from fouling sooner.

[skiwesser]

Thanks PKRWUD you're always willing to give advice and you know what your talking about, 88workcar & several others too, anyway I appriciate it.
Well I skipped the vac test and pulled the intake and I think it has been pulling oil from the intake gasket because #2 port is noticably cleaner than the others (on intake and head) I guess the oil is keeping dirt from sticking to the port walls, if the oil was coming by the ring it would'nt cause this way up in the intake would it? You can see it when I removed the upper,looked like #2 hole had been cleaned with solvent compared to others.