Hi I have had a good look at the threads her on Mk1 diesel heads, but no-one seems to have discussed this. I have recently got a secondhand head through ebay on the condition (at my mechanic's suggestion) that it passes a head density test. My mechanic told me that if an alloy head has been over-heated the main problem is that the heat changes the density of the alloy and this stuffs the head up for skimming and re-using. He says that the test is easily done using a tool which has a ball-bearing in a calibrated tube, the ball runs down the tube, bounces off the allow head and the distance it bounces back shows the density of the alloy.

Anyone heard of this? All the posts here talk of is warped or cracked heads, no mention of density.

While I am on a roll, if I have an unknown head, what head gasket do I get as there seem to be a few thicknesses. Do I still get a replacement for the one on the engine now even though the head is different?

Thanks