I have 1987 M6 that just went 80K. The cars runs great, except the gas mileage is a little low around 16mpg and it just passed emissions. . I changed the plugs rotor, cap, fuel filter and did a valve adjustment about 67K.

I decided to check the valves again before putting it back on the road this summer. With the exception of 5 valves all are sitting right on .28mm or little above at .30. One of the intakes and 3 of the exhaust are sitting at .25 mm. All seems fine, except one of exhaust value has zero clearance, which really concerns me. Iíve ordered a bunch of smaller shims, but wondering what are the chances the valve is fried or why it changed so much.

I guess the next step is a leak down test, though I never done one before. Can I do the leak down test while I have it apart?

Thanks for any suggestions.