overheated head
 

Hi guys, I have a serious problem, my miata nb vvt overheated a few days ago, I lowered my head and it was bent, I took it to the machine shop for a shave and it was perfect, take advantage of doing a refresh of all the stamps and a good chemical wash , a valve was lapped and so far everything is fine, when installing the valves and springs I notice that there are a lot of valves that do not seal well at one end of the seat, this leaves me puzzled, it is possible that the heating of Can the chamber deform most valve seats for this to happen? I can't find logic, help

Sorry to hear of your misfortune. If you need a 0 mile ported/polished VVT head with Tomei Cams, +1 valves and shim under bucket conversion, lmk.

How much needed to be milled to make it flat? Did the cams still spin freely?

the cams rotate freely without problems, the camera will shave .60 to increase compression.

Are you putting the valves back in the same ports they were removed from?

Yes, they are being placed in the same order, I did a test in the dark with a flashlight and a very small ray of light is seen through the seal, I don't know if it is something like that from the factory or is it really damaged, I tried another head I got from yunkyard and it was much better although the exhaust valves showed a very small ray of light on the seal. Would it then be normal?

When an overhead cam head of this type is overheated and warped beyond .2mm (.008") it should be straightened, then milled or discarded. I have saved many of these that were .25mm (.010"+) but they don't make good heads. The cams need to spin freely, meaning they can be turned easily by hand with out the lifters. These can be checked after that fact with a straight edge across the VC surface or spark plug wells. This is a very useful tip when buying a used head that has already been surfaced/rebuilt. There should be no light coming through the valve to seat face. You can lap them but on modern engines with hardened seats it is difficult to remove much material. I only use lapping to check the seat to valve face position.