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Machine shop cracked a cylinder head while redecking and milling, what should I do?

Howdy. I have a 2009 Forester X Limited with 155k miles. I was replacing my head gaskets and took the heads in for milling. Got a call yesterday that they were pretty warped and needed to be redecked. Just got another call stating that when they tried to fix the right cylinder head, it cracked in four places. They think the other head is also beyond repair. What would you suggest I do? Is there a good source for reman cylinder heads that are less than the $750/head I’ve been quoted?

RockAuto has them for $500.00 each.


They’re $500 each plus $100 core at Rockauto. I’m a bit skeptical about the ‘broke into four pieces’ thing - any folks here have experience with that kind of problem?

Word choice mistake on my part- they said “cracked in four places.” I’ll correct that now.

Holy bejeezus Tester. You helped me out something like 7 or 8 years ago when I was replacing a head gasket on a 2003 Mitsubishi Eclipse. Never would’ve made it if you hadn’t helped me out, so much appreciated!

You’ll probably get socked for the core charges, especially if one is already damaged beyond repair.
Try Ebay instead.
I see lots of options over there and a lot less pricey…

It’s very easy to crack a warped cylinder head with modern vehicles. There’s just not much material left as there was in days past.

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Did the engine suffer overheating with that being the reason for the head gasket replacement?
If so, this can often mean piston ring/cylinder wall issues which in turn can mean oil consumption problems once reassembled.

It’s not unusual for Subaru heads to warp a bit. For a Subaru head to crack due to milling there would have to be some serious issues with it due to major league overheating or someone trying to shave too much off in one swipe.
The maximum that can be milled off is .020 of an inch.

I think if you can get new, good quality heads for $500 each, you are golden! That’s the way to go, as long as you are sure the bottom half of the engine is in good shape. Did you check the lower engine deck where the heads bolt to, that it is straight (flat) enough?

That was something that caught me off guard- there was no indication of overheating. The whole thing started with me noticing a burning oil smell and tracing it back to a leak between the short and long block on the right side. I had oil leaking at a slow-moderate rate (maybe a couple drops per hour), so I topped it off and took it in. I asked them to do a once-over before I go on a road trip, not to check for a head gasket leak, so I was confident in the diagnosis when they came back with the same answer.

As far as the cracks go, it occurred as they were redecking the cylinder heads. I haven’t seen the process, but it sounded like they put them in a device similar to a press and force them back into shape.

Here is where in the process they likely cracked your head-

If the face of an aluminum head is warped, don’t assume the only way to straighten it is to grind metal off the face until it is flat again. The whole head is warped. If the head has one or two overhead camshafts, the cam bores will also be misaligned in most cases. The best fix here is to straighten the head BEFORE it is resurfaced. This can greatly reduce or possibly even eliminate the need to remove more than a couple thousandths of metal.

Aluminum heads can be straightened by countershimming the head on a heavy steel plate (place shims under either end of the head to offset the amount of distortion), clamping it down, then heating it in an oven to about 425° F for several hours, then letting it slow cool. The goal is to get the cam bores straight. Once they are in alignment, chances are the face of the head will be reasonably flat, too, and require minimal machining to refinish the surface.

Another method for straightening aluminum heads is to use a torch to head the top of the head, starting in the center and working towards the ends. The trick here is to keep the head temperature under 500° F to prevent softening the head too much.


Excellent link, TT.
If it were mine, I’d be inclined to just replace the heads. :relaxed:

Someone here posted a photo of one Subaru engine with the head removed, and the design was striking. It had very large openings for the coolant path, which seems a good thing, but the downside was it sort of looked a little flimsy b/c of the overly large coolant areas left sort of thin-looking walls at the perimeter. Perhaps that was also involved in making it tend to crack a little easier during resurfacing.

The machining limit on those cylinder heads is .004". That is just a little more than a clean up cut so it is straighten or replace for modern engines.