Anyone know GM small blocks?

[Matt74]

I bought a '91 Pontiac Firebird 5.0 TPI a couple of years ago for my son Ewan.
It was a project due to the metal coolant pipe that runs around the engine to the oil filter housing and rad being corroded resulting in a loss of coolant.

I replaced the coolant pipe with an aluminium one, flushed the radiator and the block until the water ran clear. It was black like old oil to begin with which was a concern!

I was hoping that the engine hadn't been over heated and it did run fine for several minutes until it warmed up and then began to misfire.
With the cap off the rad the water (no antifreeze added yet) was becoming a grey colour with lots of bubbles which seemed to have exhaust gases in them and it certainly smelled of exhaust fumes.

I assumed that the engine must have over heated so I put it on the back burner for a couple of years due to other projects.

So I've finally got back to it and pulled the heads today expecting to see something obvious but the heads are flat and the gaskets do not appear to have failed.

Some of the water galleries on the drivers side are partially blocked though with one hole completely blocked and the crud does seem to be pretty dark in colour.

As the heads haven't warped I thought I might find some cracks in at least one of the heads but I don't see any.
I need to remove the valves next but the spring compressors I have are not up to the job so I will need to source one!

The exhaust valve on number one cylinder has a thick white deposit on it.
I'm not sure if it's due to oil or a weak injector. There was no white smoke from the exhaust so I don't think it's coolant!

Am I missing something obvious as I really was expecting to find a warped head or significant cracks.
I will magnaflux the heads once I get them cleaned up and remove the valves!

IMG_20240603_122935.jpg (95.83 KiB) Viewed 2716 times

IMG_20240603_122925.jpg (101.18 KiB) Viewed 2716 times

[Pete]

Cracked Water Jacket somewhere = check the Bores for pin holes...

[Matt74]

Cracked Water Jacket somewhere = check the Bores for pin holes...

Cheers Pete. I did cast my eye over them quickly but no more than that so will take a proper look shortly.

[Pete]

SBC's have water in the inlet manifold so also worth a check and gasket seals too....

[Matt74]

All looked ok as I removed it but will take another look in case I missed something.

[Matt74]

All looked ok as I removed it but will take another look in case I missed something.

Looks alright. There is exhaust going into the intake for the egr valve but I can't see that the exhaust would make it into the coolant via the intake.

I will give everything a thorough clean over the next couple of days and re-examine.

The heads are very sooted up which I think is due to the O2 sensor being removed when the headers were installed at some point.
I fitted a new Y pipe shortly after we bought the car and added a socket to that for a new sensor with pre-heat but I think ideally it needs to be closer to the head.
It did seem to help make it run better until warmed up when the miss firing starts.
I had assumed the misfire was due to the suspected head gasket failure but as they look ok and I'm yet to find any cracks the misfire must be a separate issue!

[Dave999]

bottom left No.1 and 2 in the first picture and left top of no.2 and no.3 in the second picture

staining that extends from the flat face into the combustion chamber across the sealing ring line?
staining linked to a orange rusty passage in the head in each case?

can't be sure...did that happen when you took the heads off? or is it indicating something else? does it rub off?


I chased a similar problem over 2 partial rebuilds head and gasket examination was never conclusive wasn't like i'd blow part of it out. even took the head to be checked for cracks

was the gasket or the head sealing surface
Think i ended up getting a minimal few thou off the head and a standard monotorque "rebuild kit" gasket.

Dave

[Matt74]

bottom left No.1 and 2 in the first picture and left top of no.2 and no.3 in the second picture

staining that extends from the flat face into the combustion chamber across the sealing ring line?
staining linked to a orange rusty passage in the head in each case?

can't be sure...did that happen when you took the heads off? or is it indicating something else? does it rub off?


I chased a similar problem over 2 partial rebuilds head and gasket examination was never conclusive wasn't like i'd blow part of it out. even took the head to be checked for cracks

was the gasket or the head sealing surface
Think i ended up getting a minimal few thou off the head and a standard monotorque "rebuild kit" gasket.

Dave

Hi Dave,

Well spotted. Those areas do look suspect in those photos.
I don't think those marks were caused by me.

Heads are back on but I haven't started it yet. I bought myself a 2.8 Capri that I plan on using as a daily so that took priority as I wanted to get it road worthy before winter.

Didn't happen thanks to coming down with Covid and now I'm in the middle of painting the Charger.

Will get back on the Capri and Firebird when the weather improves.

Will update on the Firebird when I get around it.

I think I remember reading about your suspected head gasket issues. I must admit I'm in no rush to start the engine on the Firebird in case I haven't fixed the issue but fingers crossed I have.