theczechone Posted February 18, 2014 Share Posted February 18, 2014 So I've started working on a N42 cylinder head and after a through cleaning of the combustion chambers I noticed small hairline cracks in between the intake and exhaust valves. I need to cut out the brass intake seats anyway so that is my next step to examine the crack further. But is this pretty common? Am I likely to run into the same issue with any other N42 i may get? Took the head to a local welder that does repair on aluminum race blocks and he said that he's seen that before on these heads, but the water jacket is deep in the casting so it's unlikely to leak. And even after repair the same problem would manifest itself again. The head was pressure checked before I bought it too. How likely is this head to survive a higher horsepower situation? Not sure of the numbers I would be running but comp ratio about 10.5:1 and still toying with the idea of around 8000rpm with all new valve train and forged pistons. Quote Link to comment Share on other sites More sharing options...
theczechone Posted February 19, 2014 Author Share Posted February 19, 2014 anyone? Quote Link to comment Share on other sites More sharing options...
NewZed Posted February 19, 2014 Share Posted February 19, 2014 (edited) Monroe says that cracks between the valve seats is the end of the head. Page 90, How to Modify... The thing about cracks is that they like to keep growing until there's no material left to stop them. Edited February 19, 2014 by NewZed Quote Link to comment Share on other sites More sharing options...
theczechone Posted February 20, 2014 Author Share Posted February 20, 2014 Thank you, I've had similar thoughts. Quote Link to comment Share on other sites More sharing options...
Xnke Posted February 22, 2014 Share Posted February 22, 2014 A lot of the MN47 and E30 heads crack there, and it's nothing to repair the crack if you're already pulling the seats. Carve the head out to the water jacket and weld it up solid, re-cut the seat counterbores and install the new seats. You'll have the head ported anyway if you're looking to spend the cash to run an 8000RPM L28, so it wouldn't be a big deal. What is a big deal is that the cracks indicate that the valves have been run very hot, and the head has been run very hot, so you may find other problems later. I would go over the head with a fine-toothed comb if it was my engine. Quote Link to comment Share on other sites More sharing options...
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