Overheated M42: the depressing saga

[bmwpower]

Long story short = cracked head

Almost the same friggin spot as mine.  WTF is with these heads dying?

[nomad]

Because this is a large hole that comes closest to the cylinder so it is extremely prone to cracking once heat goes unchecked.

So why is the head gasket shaped this way? With "blocked holes" (the elliptical holes and odd shaped one) for coolant? I'm almost tempted to ream these out a bit on the new headgasket to ley the coolant flow better. Hopefully those Germans knew what they were doing but they certainly got the large hole wrong.

What's the point of having large water holes if the head gasket covers them up? I'm confused since the head's elliptical holes would mate perfectly with the block's elliptical holes.

Anyone know?

[bmwpower]

One thing that comes to mind, and this is merely a guess, but those same types of holes are on my M30 as well.  I'm thinking it has something to do with the fact that if the hole was wide, there would NOT be sufficient back pressure to fill the entire water jacket void.  With a small hole, the coolant backs up and has a chance to fill the entire jacket, then start flowing.  Make sense?  You don't want hot spots.

[nomad]

Just seems retarded though. Why have such a large hole right next to the chamber if you only need a tiny 1/8" hole?

So I think my crack was there befroe I bought the car, I could be wrong though. See the shiny cylinder? The coolant got all the crud off the piston.

[nomad]

I think I know why the holes are that way.
The inlet for water is from the bottom of the rad to the thermostat and the water goes into the bottom of the block. The water pump pushes the water through the block towards the back. When it hits the back it goes up the water jacket, through the four elliptical holes into the head, where it flows back towards the front of the engine and dumps out the thermostat outlet pipe into the radiator. If the holes in the HG were all really large then the coolant could not "flow" from front to back, up top and then back to the front. It would just stagnate. The holes make sure there is pressure regulation and cross flow but they help keep things moving.

Like you said, backpressure to keep it flowing.
I still don't like how they put all these large holes next to the cylinder head yet only need small holes.

[nomad]

Hopefully there is a light at the end of the tunnel. A local machine shop will pressure test and resurface the head for $100 and if the crack needs repair it'll be another $100. Not too bad if you ask me.

The guy was really knowledgeable and put me at ease knowing he knows his junk. He said that in his experience, if it pressure tests well then it was the headgasket that failed and let water in, not the crack unless it is deep and large. If it tests well then he said put a new headgasket on and run it. It won't open up unless it is allowed to overheat again.

He said the headgasket failing causes the head to crack, not the head cracking and causing the gasket to fail.

The cool thing was that he immediately said "is that the engine with the sensitive timing case alignment?" "I believe the timing cover has to be machined too".

BINGO! We have a winner.

[bmwpower]

$100 to weld the head?!?  That's cheap.  I've been told multiple times that either it's not worth it to weld it - either it's too expensive or it won't hold.  Did the guy actually look at the head before he told you that?  The reason why I ask it because my crack (similar to yours) travels a good ways up the water jacket, well beyond where a welder would fit.  It may even be up into where the valve guide seats - I can't tell since the valves are still in there.  The only way he's going to be able to tell is to pull the valvetrain and take a look inside the valve area.

I just dropped both my heads (good used one and cracked one) off at the machine shop today.  I should be getting a call back on Monday after the clean and check the used head.  I didn't think to ask more about the welding of the old head, but the machinist wasn't there so I probably wouldn't have gotten an answer anyway.  If it's not much, then maybe I will fix the old head, clean and machine it and then sell it or hold onto it for an extra.

As far as pressure testing it and then running it WITHOUT fixing the crack...I dunno.  I don't feel safe doing that.  Do they pressure test it under running temps?  That crack will more than likely open more as the temp goes up.  Think about it, it's right next to the cumbustion chamber.

Sensitive timing case alignment?  Never heard of that, but I knew the timing case needs to be skimmed if the head is.  My M30 was the same way.  Of course, I forgot mine today so I'll be making another trim assuming everything checks out ok.

Hopefully there is a light at the end of the tunnel. A local machine shop will pressure test and resurface the head for $100 and if the crack needs repair it'll be another $100. Not too bad if you ask me.

The guy was really knowledgeable and put me at ease knowing he knows his junk. He said that in his experience, if it pressure tests well then it was the headgasket that failed and let water in, not the crack unless it is deep and large. If it tests well then he said put a new headgasket on and run it. It won't open up unless it is allowed to overheat again.

He said the headgasket failing causes the head to crack, not the head cracking and causing the gasket to fail.

The cool thing was that he immediately said "is that the engine with the sensitive timing case alignment?" "I believe the timing cover has to be machined too".

BINGO! We have a winner.

[nomad]

This was on the phone. The sensitive timing case alignment refers to the profile gasket. The timing cover where the thermostat bolts into needs to have the surface milled off the same amount they take off the head or it'll hang down lower once the bolts go in.

Once he pressure tests it and examines it he'll know how bad the crack is. If it's bad and can be welded then what he has to do is grind out the area where the crack is, then heat the head up, weld to fill in the channel he created, and then machine it all back to spec, do a valve job etc.
I'll find out what the real deal is once I take it there.

I'm not too keen on running the head without fixing the crack either. If it tests ok then I'll think about it though. I'm thinking just have him do it, weld the crack and call it a day. There are lots of places that do this every day to get cars back on the road. This ancient 4cyl isn't that special.

[nomad]

OK, so I'm really starting to think the guy knows his stuff.
HE said the headgasket is what "typically leaks", not the cracks which are caused by the headgasket and the heat.

So I examined the head, the block and the headgasket itself and see for yourself in the photos above.

There was coolant inthe two central cylinders. The third from the left was really the bad one.

See how the piston head is clean from the water? The others are dirty.

Look closely at the cylinder head, headgasket and the block surfaces where the headgasket seals it.

The head is shiny clean where the gasket surface mounts tight. BUT there is a stained brown section on the head sealing surface where water was leaking in.

The headgasket sealing surface is stained a varnish brown on the good seal surfaces but the corresponding water leak has cleaned it off to shiny metal.

THe block mating surface is the same, brown at the seal, clean where the headgasket had presumably warped and let water leak in from the adjacent water jackets.

So, the crack is not good, and is certainly not factory perfect. But the headgasket looks to have given way in several places, letting water seep into the cyl. The headgasket could be the main culprit here. The crack may open up and introduce some negative aspect but the headgasket certainly warped when the car was overheated due to the plastic water pipe breaking and letting coolant out.

Thoughts? Am I just a simpleton who doesn't see the big picture?

[bmwpower]

Yea, so the question is why did the headgasket fail.  I guess we could only assume whoever had the head off last time (maybe BMW) didn't do everything necessary to make sure the headgasket wouldn't fail in the future.  I'm referring to the profile gasket issue that dealers had to repair back in the day.

This may be the same thing with mine.

However yours and mine both were running green coolant.  Something I don't do on my other cars...never have and never will.  I don't trust the green stuff.  So whoever the previous owners were, either they had a bad profile gasket job OR they didn't keep up on the maintenance and did something to compromise the fragile cooling system.

[nomad]

I'm almost positive the PO didn't keep up with maint.
As evidenced by the car needing absolutely everything maintenenced!

They definitely did the profile gasket fix at some point.

I just think this car's cooling is critical so that it doesn't overheat. When it does overheat, bad things happen. The car ran fine for the whole time I had it until the reason for the initial post - cracked water pipe - dumped the coolant steadily on the drive home and the temp pegged. I admit, I was driving in stop and go with the A/C on and don't spend much time staring at the temp guage. When I looked down at a light it was pegged. Hot as you can get it. That was surely enough to cause any problem, or make any other problem worse.

[bmwpower]

I'm almost positive the PO didn't keep up with maint.
As evidenced by the car needing absolutely everything maintenenced!

They definitely did the profile gasket fix at some point.

I just think this car's cooling is critical so that it doesn't overheat. When it does overheat, bad things happen. The car ran fine for the whole time I had it until the reason for the initial post - cracked water pipe - dumped the coolant steadily on the drive home and the temp pegged. I admit, I was driving in stop and go with the A/C on and don't spend much time staring at the temp guage. When I looked down at a light it was pegged. Hot as you can get it. That was surely enough to cause any problem, or make any other problem worse.

What pipe burst?  I better check mine...

[nomad]

Look at the 6th post or so on page one of this thread.
I posted a photo. This is a hard plastic "water pipe" that attaches intot he block with an O-ring and two bolts. There are three coolant pipes attached to it and the top pipe just gave way right at the joint of the plastic nipple.
It's $25 at the dealer, you have to take the intake mani off to get to it but darn if it isn't cheap insurance to get a new one. At 156K mike was brittle and the plastic stayed in the block when I took the part out. It should have been made of metal if you ask me.

[nickmpower]

hey man, theres no way you want to use that head for anything other then aluminum recycling. That thing is going to leak like hell into the cylinder and welding them is really sketchy. Just find another head and be done with it

[nomad]

I'd love to spend $1000 on this fix but I can't.
Where are you finding all your cheap heads? I'm having trouble. I see fully rebuilt ones for $675 and a used one for $200 privately but the guy won;t give me pics of it to prove it's not cracked too.

I should have never bought this car.