Question for automotive machinists: cyl. head problem

[CudaMike]

I have a pair of the bare 360 swirl port heads from MP (casting #576). The valve seats are only roughed in from the factory. One head has been drilled and has valve guide sleeves pressed in. They are 1/2" O.D. and are knurled or grooved on the I.D. The valve guide bosses on top of the head are about .640" in diameter and champfered like any stock head. However, at least two of these bosses are cracked, apparently from the sleeves being pressed in. I tried inserting a valve stem into the valve guides but it wouldn't go, as the guides apparently haven't been reamed to finish size. My question is, how bad of a problem are these cracks? What would be the best course of action to repair that head? What are the options? Thanks

[Billydelrio]

CudaMike
I am not a mechanic or machinist, but I believe I have seen what your are seeing. I have had guides replaced and the heads come back from the shop with part of the original boss completely broken off. When I machine the guides for the .500 seals, all the broken and craked part of the original guide is machined off anyhow. This is one of the reasons that I made the switch to the thin liners, rather than the large guides.

How does the port end of the guide look?

Billy

[Tarrbabe]

I am not a machinest, but I have seen heads with cracked and even with the towers broken off. In some cases you can mill the tower down to remove the crack and thus stop future cracking and if you run teflon seals, you will have to mill the towers anyway. The heads I saw were Chevy and ran on round track. There was no excessive oil by-pass as the heads had bronze guides installed and the engine screamed at 7500 rpm all night. I know the heads were Chevy but the science is the same.

[biggerhammer]

as a machinist, I see a lot of cracks at the top of the valve guide, especially when they have been replaced by some mass re-builder. I personally machine the cracked bosses down to remove the cracks so they won't travel, (yes, they can /will continue and sometimes go to the water jacket). On some heads the lower boss can be a problem by allowing the valve to move lateraly instead of down, so you need to support it somehow, like putting in an oversize guide(lengthwise oversize) and machining it to fit the seals. By the way, if you have any cracks, spend a little extra and pressure test the head, cheap insurance.