'71 BMW e10, straight 4. Number one and two cylinders have ZERO compression. 3 and 4 are strong. (Being a fucking BMW, it* STILL* runs!)
Took off the valve cover and it seems everything is pogoing as it should. No broken rockers or anything. Oil is clean, so no evidence of coolant mixing it up in there. Can’t verify if the coolant was being blown out the exhaust (shut the car down soon after it ran like shit, let it sit in hot temps and now system is pretty dry and barren, a rocky place where my seed will take no purchase, but I digress…)…
Engine spins and no indication of a rod blowing out the block or anything like that.
Head gasket or a should I tear it completely apart? Of course, once the head is off, it will answer a whole lot of questions that may crop up twixt now and then…
Whether you just top it or do the full overhaul is your call. If the cylinder deck is much eroded you’re gonna end up with a full teardown whether you want it or not.
At the other extreme if you’re real fortunate and A) the gasket only tunneled and B) you caught it early then maybe C) the head doesn’t absolutely need resurfacing and you can get by with just a new gasket.
Overall it depends on just how far redneck shadetree you want to do this versus how long you want to keep the beast alive in good form.
You forgot number 4, this happened on a Chevy Equinox I had. The head gasket blew between the cylinder and the corner between the head and the block. You could see the air/fuel mixture shooting out of the tiny hole in the gasket. When I pulled the head, there was a spider web crack in the gasket between the cylinder hole and the edge of the gasket. Slapped a new gasket on and it ran great.
And I’m pretty damn redneck shadetree. I’ll just pull the head, slap a gasket on it and keep driving it till I die. Nice thing about this car is, it just gets more valuable every day simply by existing. Unless I wreck it, I can’t really hurt it.
oh yeah, there’s other ways they can fail, I was just putting out the most common ones I’ve seen. I did have a truck (old diesel F-250) which had the head gaskets fail by leaking oil down the sides of the engine (early Dodge Neon owners know this one too.) But today’s multi-layer-steel (MLS) head gaskets rarely fail like that anymore barring a design flaw. the old style graphite/fiber/metal mesh gaskets were good for a while if your engine was iron block and head, but with aluminum heads they’d rarely see 50,000 miles. MLS gaskets seem to last forever.
yeah, there’s that. many moons ago I worked on a Chrysler or Dodge something-or-other with the 2.2, and the head gasket blew like this but the owner ignored symptoms until the car basically quit running. I don’t remember how large it was, but at the site of the failure there was a “channel” eroded between the two combustion chambers. Trashed the cylinder head.
I have a #5. A pressure oil passage went up the the valve train near the edge of the block and head. Oil first started to seep; then leak; and next squirt out between the head and block. This was on a British Leyland O-series engine.
There’s the cylinder(s), oil galleys, coolant galleys, and the outside world. A gasket failure can connect any two (or more) of those things. In terms of pressure, cylinders are both the highest max and the lowest vacuum from cycle to cycle. While each is always at a different pressure from its neighbor(s). Oil is next highest, coolant next, and the outside world is, by definition, ambient. So the gasses and fluids will flow from high to low pressure.