I have a pair of 340X heads that I planned on using on my 72 Duster 340. They are fully ported and polished, they have the valve spring seats worked over for vitton seals and dual valve springs, they have bronze guides, and they basically have a ton of work on them. I took them to a local machine shop to get them checked and resurfaced and they found 2 cracks on one head and 3 on the other. The cracks are in exactly the same place, between the spark plug hole and the intake valve seat. I am not sure what to do and neither does my machinist. I attached some photos in the hope that someone can tell me what to do. The machinist suggested opening up the spark plug holes and putting inserts in them and new steel valve seats, but he is not sure of where the water ports are on these heads or how much of an issue this is on these heads. He said that certain cracks on certain heads are quite common and do not affect anything, and other cracks on the same head might mean a direct trip to the trash can. I am sure that there have to be some old school cast iron cylinder head gurus here that will now what to do and if these heads can be saved or if they are destined for the scrap yard. I live in East Texas, and someone may know of a place in the area that maybe specializes in this type of work, or on Mopars.
340 X heads cracks between spark plug hole and intake seat
- Thread starter HSDemon
- Start date
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"My machinist doesn't know what to do" is code for "find another machinist". You pressure test them. That's what you do. If he caint figure that one out, he's not a machinist.
HemiSSDart
Dartus Interuptus
Get them pressure checked and if they don't come out too bad run 'em!
I had the same problem all 8 cylinders were cracked like that ,but it was running 13 to1 and the heads were milled .060 and 50cc. Chambers on a 365 cu. In 2barrel Holley no one could answer the same question
They are ok.
That happens when the plug is too hot and holds too much heat in that part of the head.
In other words, it’s a tune up issue.
Edit: I forget to mention you don’t just slap a valve job on it and go. You MUST put a seat in there.
And I never use hard seats under an intake valve. Use ductile iron. Since you need two of them I’d do all 8 and suck up the cost.
That happens when the plug is too hot and holds too much heat in that part of the head.
In other words, it’s a tune up issue.
Edit: I forget to mention you don’t just slap a valve job on it and go. You MUST put a seat in there.
And I never use hard seats under an intake valve. Use ductile iron. Since you need two of them I’d do all 8 and suck up the cost.
From what I can see it seems to be fine as long as they pass a pressure test and I put new seats in them? The machinist suggested to open up the spark plug holes and put inserts in there, any idea if this should be done or if it would be worth doing?
Thanks man, any other opinions?
Run it. If you did not pull it apart you would had never known.
Cracks in old cast heads happen. It it is not spewing water or oil everywhere run it and search for another set of heads for “down the road.” Ya know… as back ups.
Side note: average machine shops that cannot afford comebacks say what yours did. They do not want the liability of your engine puking and you saying it was from a bad head. Can’t blame them.
Cracks in old cast heads happen. It it is not spewing water or oil everywhere run it and search for another set of heads for “down the road.” Ya know… as back ups.
Side note: average machine shops that cannot afford comebacks say what yours did. They do not want the liability of your engine puking and you saying it was from a bad head. Can’t blame them.
Yes, that is what I gathered from the way he was talking to me about it. He said that he could not guarantee that the heads would go another 30,000 or 1000,000 miles after putting in new seats and maybe spark plug inserts. I know that I will never drive this thing another 10,000 miles in my lifetime, someone else may after me, but I sure ain't.
If you do not install a seat the fracture will continue to migrate until the head does fail.
A ductile iron seat will stop it. You can use a hard seat but I prefer ductile iron for intake seats.
This ^^^ That's how cast iron acts. Unless the crack is stopped by drilling a hole in the ends, OR finding an edge as in the case of installing new seats, it will continue to migrate and will probably eventually migrate into an area that does have water. That would suck, especially if they pass a pressure test NOW. So I agree. Pressure test first, if good, put seats in. Thing is, unless they have hardened exhaust seats now, they need all 8. Like @Newbomb Turk said, you should go ahead and replace all the intakes with ductile iron seats, exhaust with hardened seats. I just spent over a grand of your dough. I'd be lookin at new heads. JMO
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PRH
Well-Known Member
I’d pressure test them, and if they passed that test, my advice would be to just run them.
All the talk of new seats, etc, you’ll end up with another $1000 into cracked heads.
Your $$$$, your choice.
All the talk of new seats, etc, you’ll end up with another $1000 into cracked heads.
Your $$$$, your choice.
Exactly. Just not somethin I'd do.
and that's just seats!
so you're gonna do that, you might as well go ahead a do guides while you're there. then, what's up with the valves?
all of a sudden you've got 1500 wrapped up in set of old *** heads...
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Just curious, what's keeping the seats from falling out?
Correctamundo. Much more to it that just seats.
"Old ***" I guess is somehow older and crappier than just "old". lol
Good, correct machine work.
Pressure test, if good run them, if leaker ,send them to the scrap pile.
If the guides are good why change them? That makes way more work.
At minimum he needs two seats IIRC. Since I don’t like cheese dicking out because when you do it comes back and bites me in the ***, I’d do all the seats under the intakes.
The OP doesn’t need to do it but I would which is why I said it that way.
His shop is already sketchy on it.
Run-em
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