Engine head alignment pin holes out of round

[eburrows]

Hey all, I'm doing my head gaskets, due to white smoke and bubbling coolant a few weeks ago. When I got the heads off, I noticed that all four holes for the alignment pins (two holes, on each head) were out-of-round, looking like they got pulled outward. It's only a millimeter or two, but it's enough to cause a bulge of material in the head surface of about 2 thousandths of an inch, possibly enough to be the cause of my gasket failure. Anyone know what would cause this?

 

[kris812]

The real question is what does the Dowl Pin look like? Looks like the pin was bent and went in a little sideways from torquing the heads down.

I would look into changing the Pins, and taking the heads to a shop to at least mill them flat. Run a straight edge across the heads at the very least the check, and file it down flat in a pinch!

Took 6 passes on their machine to get my heads flat when they were off. P/O did head gaskets before me at a dealership (ouch), and they left some of the OEM gasket material on the heads and put them back on bent like a Banana.

 

[eburrows]

@kris812 I checked the heads with a straight edge, and they're OK. I'm going to check the block as well.

I can't see anything amiss with the block alignment pins, but they barely stick up, so I'm not sure I could see if they were crooked.

I'll definitely flatten the heads, though your story makes my head spin. Here I am gently polishing off oxidation marks from the old gasket, and your old dealership left chunks of gasket on! Yikes.

 

[kris812]

Any updates on this?

2 things to check really closely for while your heads are off! See if ANY cylinder liners are coming loose (look for ring cracks around cylinders. Also look over your camshaft for worn lobs.

Otherwise I don't think the Pin does anything besides hold it in place for bolts. Just make sure it doesn't hold the head UP whenever you test place the head on engine without a gasket.

 

[eburrows]

Any updates on this?

Finally finished the head gasket job this week. I checked all the liners, and even did a dye crack check on every cylinder and the heads. Everything looked ok and other than that bump next to the pin hole the heads were within spec for flatness. So I milled the bumps down myself and reassembled everything, using studs instead of stretch bolts this time. So far, so good, but it's only been 50 miles or so yet.

 

[eburrows]

My engine blew again! After just 100 miles or so. Coolant in the oil. :-(

I'm pretty confident in my head gasket job, that the block and heads were flat, and there were no cracks in the castings or pinholes in the liners.

I'm not 100% confident, so it could be just another blown gasket, but is there anywhere else where oil and water could mix?

 

[StangGT5]

When you say the heads were in spec, was that based on your flat edge test or a machine shop milling them flat?

I'm hoping you had a good machine shop check them. If not, the HGs can fail even with a tiny bow. That'd be my best guest if they haven't passed through a shop.

What year Disco is this on? D1s and early D2s had oil coolers, but I think only the D1 passed through the radiator. Never seen one mix though.

Studs can crack the block, but it's pretty rare. The general consensus is that it's due to the old, higher torque specs. Obviously too loose nuts/studs will allow a failure too.

 

[p m]

Studs can crack the block, but it's pretty rare. The general consensus is that it's due to the old, higher torque specs. Obviously too loose nuts/studs will allow a failure too.

Leftover oil or coolant in bolt holes can crack the block easily.

 

[kris812]

My engine blew again! After just 100 miles or so. Coolant in the oil. :-(

I'm pretty confident in my head gasket job, that the block and heads were flat, and there were no cracks in the castings or pinholes in the liners.

I'm not 100% confident, so it could be just another blown gasket, but is there anywhere else where oil and water could mix?

The Radiator could be busted inside, mixing oil and coolant; but would be pretty rare to do so.. Could disconnect the oil lines to it and maybe pressure/vacuum test that part of the Radiator. Far-fetched idea, but it IS another spot to mix..

 

[eburrows]

When you say the heads were in spec, was that based on your flat edge test or a machine shop milling them flat?

Straight-edge and flashlight on the block with new straight-edge bought just long enough to make the diagonal. (not a bit of light) And dial test indicator on the heads. Spec is 0.002, and I saw 0.001 max on the heads.

Leftover oil or coolant in bolt holes can crack the block easily.

I chased every thread, cleaned with acetone and blew out everything. Studs were snug in the block and torqued to ARB's numbers on the nuts.

The Radiator could be busted inside, mixing oil and coolant; but would be pretty rare to do so.. Could disconnect the oil lines to it and maybe pressure/vacuum test that part of the Radiator. Far-fetched idea, but it IS another spot to mix..

Good suggestion, but this is a 2000 D2 with dedicated oil cooler.


Sounds like either I flubbed the gaskets somehow, or there's a crack I didn't see.

 

[StangGT5]

Yikes. I can't imagine doing all that labor and not having the heads machined, especially when the truck showed clear signs of a blown head gasket (smoke and bubbling coolant). Hell I barely trust a Rover engine after an overheat even with machine work. For $250 a set, that's just not worth having to do the same job twice.

My best guess is that your heads warped a little corner to corner (hence out of round/pulled dowel holes) when it originally overheated, and throwing them back on without machine work has caused the HGs to blow again. In 22 years I've never seen anyone do a HG job on an overheated engine of any kind without machining the heads. That's just a standard step on the job. Of course, aluminum blocks can warp too. But, that's incredibly rare and it's all just a guess.

Good luck...

 

[rovercanus]

A blown front cover gasket can mix oil and coolant.

 

[discostew]

The front cover can leak a massive amount of coolant into your oil.

 

[eburrows]

The front cover can leak a massive amount of coolant into your oil.

Thanks discotew and rovercanus, that's a great suggestion. Probably worth doing before making any more drastic decisions.

 

[eburrows]

After a front cover gasket replacement (what a PITA), and a couple hundred miles of driving, I think it's safe to say my coolant leak was the front cover seal. I wish I had thought of that before I did the head gaskets! I believe my gasket failed at the top-right side, between the coolant port to the water pump and the timing chain space. When I removed the cover, the gasket looked especially crumbly there.