No compression in cylinders #2 & #$4
 

Hi,

Had my engine rebuilt by a local builder a few years back after it threw a rod bearing. Engine is a 455 block, new rotating assembly from Butler. Changed the cam to a smaller XR288HR 288/294, 236/242,.520/.540, 110 for a more streetable setup. Heads are 87cc Edlebrocks from the late 90's.

I say a few years back, but looking at the receipts, it was 2013. After the engine was rebuilt, it sat on a stand for a few years while I restored the car. Finally got it back in the car. Engine has less than 300 miles on it, has never run right. Low idle vacuum, poor power, started popping through the exhaust on acceleration. I had an EZ EFI on it, and at first chalked up to my lack of knowledge on tuning.

Finally decided it wasn't the EFI and did a compression test. No compression on cylinders 2 and 4. Check the adjustment on the valves, still nothing. When installing the throttle body several years back, I had dropped a nut down the throttle and it had fallen through an open intake valve into a cylinder. I had to pull the head to get it. I was thinking maybe I had reinstalled the head incorrectly (I didn't respray the block with the copper spray) and that caused a head gasket leak now, which would explain the lack of compression and #2 and #4. Pulled the head. Maybe I don't know what I'm looking for, but the head gasket looks fine.

Pictures of attached. Clearly no combustion in cylinders 2 and 4. There's a pit in the top of cylinder 4 between 4 & 6. Doesn't appear to go through the deck.

I'm tired of learning at the school of hard knocks, would appreciate some wisdom. What else could cause the lack of compression on 2 & 4? Can you see a leak in the head gasket? Is that pit in the top of the cylinder a show stopper?

Thanks for your advice!

Can't really see a reason for the lack of compression for the 2 cyl.
The pic of the head looks like the exhaust valve is not seated all the way, but probably illusion from photo.
Too bad you didn't do a leak down on them.

I'd remove springs and vales and check for bent/burned valve(s).
With exhaust noise when running probably exhaust side of the problem?


:confused:

I regret not doing a leak down test as well. I was so certain it was the head gasket I didn't think I needed to bother.

That pit in the deck is letting combustion gases undermine the fire ring of the head gasket, and proof of that can be seen in the head gasket.
Your going to have to jank and disassemble the short block and get that hole pinned and then the deck will need to get milled.

I can’t tell from your photo, but as long as that pit does not extend down to close to the end of where the ring travel stops it should be repairable.

Your head looks fine , but I would get them both milled .002” by a shop that can provide the needed near mirror like finish that will promote long gasket life.

When you put the heads back on do not use any sealer on the head side of the gasket as the head needs to slide around since it expands much faster then the block does..
The mirror like finish on the heads is what keeps the heads from chewing up the gasket over time.

Also 2 and 4 look like they have never been firing since you put the motor back in the car!

looks like the valves to me too. U can poor water in the intake ports and exhaust ports to see if it leaks past the valves. If its not seating it will leak right out.

That looks like a hole more then a pit. Maybe its just the picture..

That is my feeling as well. Could that have anything to do with why there is no compression?

Stan

That pit is between #4 and #6. I would think those 2 would have no compression instead of #2 and #4?


When he dropped a nut in engine, were the heads taken apart and examined?


:confused:

Bolt the head back down with the old head gasket and apply compressed air to the spark plug holes. Who knows what you'll find. Maybe those 2 pistons are missing rings. Stranger things have happened. If you're not leaking air into either port or into the crankcase, something's probably suspect with the valvetrain.

Just to be clear I have never replaced a blown head gasket on a Pontiac. But I have replaced blown head gaskets that could be clearly seen where they had blown when you looked at the gasket. On these engines while the cranking compression was low, it was far from being zero. #2 piston does not show a great amount a burn cycles while #4 shows almost no burn cycles at all.

Stan

I must apologize, I looked thru his post too fast and missed the ingestion part,

Thanks for all the thoughts guys.

If it wasn't clear, the nut fell down the throttle body while the engine was off, so there was no damage. I just pulled the head and the nut was sitting on top of a piston.

This week, when I first pulled the rockers off to remove the head, I noticed that two of pivots on the rockers were upside down... the flat part was down on the stud, and the round part was up. I guess I installed them wrong after reinstalling the head. I feel really embarrassed to admit this. :(

Both the incorrectly installed rockers were on the exhaust valves of cylinders 2 and 4. At the time, I felt that might have made the rocker sit lower, so the valve wouldn't seat. I reinstalled the rockers properly, adjusted the valves, and did another compression test... still no compression. Is it possible that the incorrectly installed rockers wouldn't allow the exhaust valves to seat properly, and it burned them?

Charlie, I tried pouring water in all the exhaust ports. 2, 6 and 8 the water filled up the port. No water leaked past the valves. In 4, the water just runs out of the exhaust into the intake runner. All all 4 intake runners, the water just fills up, no leaks.

At this point, would it better to pull the valves or bolt the head back on with the old gasket and do a leakdown test? I don't own a valve compressor or leakdown tester, but will buy if needed.

Thanks for your help.

At This Point
 

Before pulling valves.

Check valve stem height

Prop the head up where you can push down on the valves with the palm of your hand. Feeling for weak valve spring pressure. Then feel for lose valve guides.

Worked on a engine years ago that had good compression if you checked it pulling one plug at a time. With all 8 plugs out, it didn't have any compression. Valve springs were shot. With all plugs out the lifters would pump-up and hold the valves off the seat. You would get a poof on the first spin, but if you released it with engine spinning, no more would come back.

And say again where that water went when you checked #4 exhaust.

Clay

In 4, the water just runs out of the exhaust into the intake runner.

this is a serious concern?? Sounds at best you burnt the exhaust valve with the mis-adjustment due to the pivot ball. Holding the exhaust valve open the entire time...not letting it build compression either, Now in cylinder 2 maybe not as bad but still not good. At worst you wiped the cam.

Level the head on a work bench and fill #2 and #4 combustion chambers with a soap/water mix and blow compressed air into the intake and exhaust ports. Seal the air gun up best you can with a shop towel. It will find the smallest leak at any of the seats.

To have ZERO compression my guess is that you have a big leak at a couple of the valves, bent, sticking, stuck?

That little pit/hole would still seal things up enough to show something on the compression tester gauge............

What were your compression test numbers? Were they zero, or just slightly down?

Did you reuse the gasket or install a new one? Did you spray the gasket? You said you didn't spray the block, but that's not something you normally do anyway. I see bits of copper spray on the block, and some on the valley-side of the head gasket. Is this from your last install, or left over that wasn't cleaned off while retrieving the nut?

The older Edelbrock heads weren't the best quality. I have a set that needed quite a bit of exhaust valve seat lapping right out of the box, not to mention all the aluminum porosity.

Could the clean cylinders be evidence of ingesting coolant instead of mis/non firing? That was my first thought.

Some of the aftermarket aluminum heads have pretty tight valve to guide clearances. Always a possibility that it stuck an exhaust valve in the guide.

Even though both heads would be affected, did you use the correct head bolts? Early and later edelbrock castings used different bolt kits.

Are you saying that some how the water from the exhaust winds up in the intakes port runners? That should not happen .. Pull the valve and look for a crack under it . Or maybe im miss understanding ? Can you explain this further?

I think his heads probably have the exhaust crossover holes drilled in them.
 

And the water is running out thru that exhaust crossover hole, which would put it into the crossover in the intake, but NOT into an intake port.

The heads LOOK like 87cc versions, but can't really tell from the pics.
And there is not a picture of the intake mounting surface.

I agree that if water poured into an exhaust port is actually making it into an intake PORT there is a serious problem.

Only the 87cc heads have the crossover port, the 72cc versions do not.

Looking at Cylinder #4 chamber it seems that the only exhaust soot is coming out of the exhaust valve. I would think that extreme low compression in a cylinder would produce a massive amount of soot because of the poor burn characteristics unless both #2 and #4 cylinders never fired because of bad plug wires or something else preventing spark and therefore combustion.