Cylinder head height / depth

[Richard McDonel]

Early in the restoration of my 71 240, I took the head and block to a reputable engine machine shop and they milled enough off both to true them up. Now the body's done and I'm back to the motor, I am hearing that there is very little margin for milling on these engines. By the fit of the front timing cover, I figure 12 thou. was taken off the block, but I have no idea on the head. Can anyone advise me how to tell if the head is too thin? I know I can get spacers for the cam towers, but have no idea how to determine the number and thickness I should use, if any at all. And finally, assuming it all goes together, does anyone see any reason to employ the old hot-rodder / racer trick of laying play-do or plasticine on top of the pistons, then torquing the head down, and with cam engaged turn the engine over, as a safe way of determining any possible piston-to-valve clearance issue?

Many thanks.

[zKars]

No trick to knowing how much the head is shaved, and hence how much cam spacer is needed. Look in the factory service manual to get the un-touched head thickness, subtract your current head thickness, and viola, but the magical power of substraction, you know how much spacer you need under the cam towers. You can also take some off the top of the front cover if clearances get too tight there.

There is no "too thin" until it causes valve to piston touch, or you get too close to the edge of a valve seat, or you break through the casting into water or oil passages.

If the engine turns over by hand with no plugs in (no compression) (do not use the starter!) without the slightes hint of binding, then the valves don't touch the pistons. The plasticine trick is great to find out how close they come, then you can decide if its too close or not.

[240260280z]

I took 2mm of the head in my blue 280z with no shims... it is all geometry. Shims are commonly used but there are ways around this practice.

[madkaw]

Not sure how you figure .012 by looking at the timing cover fit. If .012 was taken off the block then the cover should have been machined too.

Surely the machine shop gave you a stat sheet?

Shims can be used , but unless you are over .030 total I wouldn't worry about. You can always run the 2nd notch on the cam gear.

I'd measure piston above deck height to see if you need to run a 1.25mm HG