[JBanna]

Hello again experts! I had an issue with my engine, with valve clatter and a serious drop in oil pressure at low rpms, but only under load. I decided to pull the heads after compression and leakdown testing showed a problem with both my # 4 and 6 cylinders, so I pulled that head and found a blown head gasket between their exhaust valves, which explained the compression problems, but what could have caused this? The attached photos show the blown gasket and the condition of the cylinders, all of which look undamaged...thoughts?

Thanks again to all!

Joe

[Half-Inch Stud]

Was there pinging? Headbolts lack TQ?, low oil pSI doesn't seem to correlate. Was there antifreeze breach into CYL?

I HAD THE Same breach between CYLs 2&4 on only 1 hipo 455+060 build. Antifreezecbreached into CYL. Warped a piston's top near breach.

[steve25]

Several things might have caused that.

1) how level is the block deck and head deck inbetween those two cylinders.
More then .002” off is not good.

2) that’s a very hot area between those two exh ports and if the motor runs hot it even has overheated in the passed that head bolt above the two center exh ports will expand more then normal from the heat and that in turn reduces the clamping load that’s needed.



When this number two condition takes place over and over then the gaskets fire ring gets burned through little by little.

3) that center head bolt might not have been torqued right due to crap in the threads,
3B) or that bolt might be too long and is bottoming out in the bolt hole which will give the needed torque reading, but not the needed clamping load.

When I torque up those two center bolts I go up 100 lbs from the stock 95 just to better deal with those bolts expanding from heat.

If this is a 1973 and up casting I would knock that head apart and get it crack checked before just checking it for level and bolting it back on.

[PunchT37]

Pay attention to 3 on what Steve says. Make sure there’s not a bunch of trash in the bottom of the bolt holes.