[Sprocket]

Attached are images of the spark plugs and the compression test results. What is the problem?

[johnta1]

I'd say #3 is leaking pretty bad.
Could be a few things.


Did you try squirting a little oil in spark plug hole then do the compression test again?


Hear any weird sound/popping/huffing or something?


Adjust any valves lately?

[dmac]

Originally Posted by Sprocket

Attached are images of the spark plugs and the compression test results. What is the problem?

Are the plugs oily or dry or smell like gas? That low comp #3 is worrisome. New motor, old? Recent lifter adjustment? Cylinder can only lose that much compression through either a valve being open at the wrong time or very leaky or the rings letting a lot of pressure through.. Do you get any smoke and what color, or any backfire?

Next easiest thing to check in my opinion is valve/lifter adjustment and checking to see if all valves sit at the same height and none are loose on engine rotation- especially #3. There should be a similar amount of rocker stud thread showing at each rocker nut, or if using adjustable rocker nuts, the lock set screw should sit about the same at each stud. The compression is close enough to the same on all but #3 so look closely for an over tightened rocker. In an old motor I had with high miles and weak springs, I would float and bend valves from piston contact even at relatively low rpm. Valves wouldn't fully close and rocker arm would be loose.

A pressure test on that cylinder would be the next check if you don't just want to pull the head. Doing the checks above require no special tool and is pretty easy. The oil in the cylinder is a way to check the rings and is easy too.

[tom s]

Do a leak down and listen where the sound is coming from.Could be the intake side,exhaust side or from the pan.Tom

[PunchT37]

Running pump gas?
Those pressures remind me of my engine. Two times I had busted ring lands because of detonation. Mine had 225 psi. Both pistons made exactly 90 psi when broken. Just a thought.

[Sprocket]

More info. The engine consumed approximately 4 quarts of oil in 750 miles.

[72LuxuryLeMansLa.]

Originally Posted by PunchT37

Running pump gas?
Those pressures remind me of my engine. Two times I had busted ring lands because of detonation. Mine had 225 psi. Both pistons made exactly 90 psi when broken. Just a thought.

Wait! Did you run a High Compression Pontiac 455ci with pump gas in Louisiana heat? Did it do damage to the bottom? Do tell. Did you rev it past 5499 rpm?

[steve25]

Excess oil usage unfortunately goes hand in hand with broken rings and or piston ring lands!

Either way it would seem to be time to yank the Hood and pull the motor.

If a ring is busted then the longer you run it the more likely your headed for a over Bore job at least in that cylinder!

[PunchT37]

Originally Posted by 72LuxuryLeMansLa.

Wait! Did you run a High Compression Pontiac 455ci with pump gas in Louisiana heat? Did it do damage to the bottom? Do tell. Did you rev it past 5499 rpm?

Yep. In those days, the octane in my stomach was higher than the car`s tank. The last piston broke racing a `71 W30. Blue with black hood with a 4 speed. Nice car. I did beat him though.

[track73]

Broken compression rings IMHO. If piston lands were broke it would probably be zero. I have a 56 Buick that had 30 PSI on 3 cylinders that had broken rings. My 10:1 Pontiac 400 had zero compression with broken piston ring lands.

[steve25]

Could just be the top or second ring busted.

Anyway time to pump up the cylinder with air at BDC and listen for one of the 3 ways it can be getting out.

[Formulas]

Broken pistons and rings usually smoke alot out of exhaust very hard to ignore, a bad valve job can use oil fast and lower compression by ill seating valves and hides the burning oil better visually

[chiphead]

3,7,4,6 plugs show loss of oil control. 3 compression shows loss of compression sealing.

Leakdown test, then pull driver's head to inspect. Make preparations to pull engine.

[STEELCITYFIREBIRD]

So when does it smoke out exhaust if at all?

Always , decel, accel, idle, never?

True split dual system?tailpipe Smoke Corresponding to low compression cylinder.

PCV system not sucking oil due to unbaffled crankcase source?

Make sure you didn't lose a cam lobe on the low comp cylinder.

A little (recent and long term) history of the engine could be helpful.

Info on combo, you have (old) E heads IRRC ,oil building up under valve covers?

After logically deducing compressed air with rockers backed off will be be telling. Could be a guide, ring, valve seal, or pcv system source.

Oil in the chamber is a self fueling fire for detonation/preignition.

[Sprocket]

This is not my Grand Prix's Edlebrock-headed engine (thank god). This engine is in my brother's GTO. A little background:

Bought the car last year. All we know about the engine build is what was represented to us and that wasn't much other than it is a 455. The car was running and driving. The engine had ’70 model d-port heads that started with a 1. Do not know the second digit because it was ground off. The cam was an unknown single pattern 216/216 .454”/.454” cam (I measured it). As one can imagine, the engine was suffering from constant detonation running on 9X octane fuel, and I believe that it had been de-tuned in an attempt to minimize the problem. The detonation issue did not fully reveal itself to us until we tried to tune the engine the way we wanted. So, less than a month into owning the car, we swapped on a set of known 4X 98cc heads and a different cam. The results were fantastic. No more detonation, smoother running, and much better power output although top-end power seems lacking. The more urgent problem is that we know now that the car consumes oil like nobody’s business which led us to perform the compression test. The inside of the tail pipes are sooty, but if smoke is coming out the pipes it is not noticeable from the driver’s seat.

The exhaust is dual with x-pipe. PCV valve works fine and the line runs from valve to intake manifold fitting. The only time we see smoke is occasionally a very small amount at startup, which would indicate a stem seal leak, but it really is not much nor very frequent. The 4X heads now in use came off of a running engine that did not consume oil outside of the norm. The engine does blow oil out the passenger breather and valve cover.

It is possible that one or more of the valve stem seals are leaking, but I have never heard of oil consumption of this magnitude occurring from those. I suspected that a ring or rings in one or more of the cylinders are damaged from the detonation and causing the oil consumption, but I thought I would run this past the board to get more ideas or validate my own. We may try some of the suggestions give above, or probably just go ahead and pull the heads and then the engine out.

Oh, and to my man in Eunice: no Louisiana heat – only Texas heat!!!

[dmac]

Originally Posted by Sprocket

This is not my Grand Prix's Edlebrock-headed engine (thank god). This engine is in my brother's GTO. A little background:

Bought the car last year. All we know about the engine build is what was represented to us and that wasn't much other than it is a 455. The car was running and driving. The engine had ’70 model d-port heads that started with a 1. Do not know the second digit because it was ground off. The cam was an unknown single pattern 216/216 .454”/.454” cam (I measured it). As one can imagine, the engine was suffering from constant detonation running on 9X octane fuel, and I believe that it had been de-tuned in an attempt to minimize the problem. The detonation issue did not fully reveal itself to us until we tried to tune the engine the way we wanted. So, less than a month into owning the car, we swapped on a set of known 4X 98cc heads and a different cam. The results were fantastic. No more detonation, smoother running, and much better power output although top-end power seems lacking. The more urgent problem is that we know now that the car consumes oil like nobody’s business which led us to perform the compression test. The inside of the tail pipes are sooty, but if smoke is coming out the pipes it is not noticeable from the driver’s seat.

The exhaust is dual with x-pipe. PCV valve works fine and the line runs from valve to intake manifold fitting. The only time we see smoke is occasionally a very small amount at startup, which would indicate a stem seal leak, but it really is not much nor very frequent. The 4X heads now in use came off of a running engine that did not consume oil outside of the norm. The engine does blow oil out the passenger breather and valve cover.

It is possible that one or more of the valve stem seals are leaking, but I have never heard of oil consumption of this magnitude occurring from those. I suspected that a ring or rings in one or more of the cylinders are damaged from the detonation and causing the oil consumption, but I thought I would run this past the board to get more ideas or validate my own. We may try some of the suggestions give above, or probably just go ahead and pull the heads and then the engine out.

Oh, and to my man in Eunice: no Louisiana heat – only Texas heat!!!

The compression loss didn't come from valve seals. It is either valves not being closed or compression 'leaking' through the rings. And if the plugs are oily, you may be just blowing oil out the exhaust without burning it except for in the exhaust system so you may not get as much smoke as you would if the cylinder was firing with a clean plug. High mileage could cause ring wear, but that would usually show up across more cylinders.

I would still check for valve issues before assuming its the rings, If you had a compression test from before you swapped heads, you would know. The recent head/cam swap would have required a valve/lifter lash adjustment. That means a chance you might just need to readjust that one valve.And if you have a valve not seating for whatever reason causing the compression loss, you could still have bad valve seals making for the oil loss..

The lack of power before the head/cam swap could be from a bad cam choice. The compression loss could be as simple as a valve needing adjustment. I always check and hope it's the cheapest to fix problem, especially if the alternative means pulling the motor. The blowing oil from the breather is a sign of poor ring sealing at least, but I would check and hope its a valve issue.

[Sprocket]

Thanks Dmac and everyone. We appreciate the help.

[72LuxuryLeMansLa.]

Originally Posted by Sprocket

This is not my Grand Prix's Edlebrock-headed engine (thank god). This engine is in my brother's GTO. A little background:

Bought the car last year. All we know about the engine build is what was represented to us and that wasn't much other than it is a 455. The car was running and driving. The engine had ’70 model d-port heads that started with a 1. Do not know the second digit because it was ground off. The cam was an unknown single pattern 216/216 .454”/.454” cam (I measured it). As one can imagine, the engine was suffering from constant detonation running on 9X octane fuel, and I believe that it had been de-tuned in an attempt to minimize the problem. The detonation issue did not fully reveal itself to us until we tried to tune the engine the way we wanted. So, less than a month into owning the car, we swapped on a set of known 4X 98cc heads and a different cam. The results were fantastic. No more detonation, smoother running, and much better power output although top-end power seems lacking. The more urgent problem is that we know now that the car consumes oil like nobody’s business which led us to perform the compression test. The inside of the tail pipes are sooty, but if smoke is coming out the pipes it is not noticeable from the driver’s seat.

The exhaust is dual with x-pipe. PCV valve works fine and the line runs from valve to intake manifold fitting. The only time we see smoke is occasionally a very small amount at startup, which would indicate a stem seal leak, but it really is not much nor very frequent. The 4X heads now in use came off of a running engine that did not consume oil outside of the norm. The engine does blow oil out the passenger breather and valve cover.

It is possible that one or more of the valve stem seals are leaking, but I have never heard of oil consumption of this magnitude occurring from those. I suspected that a ring or rings in one or more of the cylinders are damaged from the detonation and causing the oil consumption, but I thought I would run this past the board to get more ideas or validate my own. We may try some of the suggestions give above, or probably just go ahead and pull the heads and then the engine out.

Oh, and to my man in Eunice: no Louisiana heat – only Texas heat!!!

Hell you're good to go then! It ain't hot in Texas! With today's gas, or what passes for gasoline anyway, I'm surprised that thing didn't come apart!

[chiphead]

A 216 single pattern cam in a high compression 455? Yeah, those pistons have been banged harder than (insert metaphor here). Leakdown test for sure. Hopefully it's not already 60 over. What cam did you have decent results with?


I'm from south Louisiana. It's not the heat, it's the stupidity. Present company excepted, of course. Never been to Eunice, but I've been to Fred's lounge in Mamou

[tom s]

Even if 60 over with that few miles a custom piston with just another 5 over should be NBD.Tom