Head gasket

[John H]

Nothing to do with sealants, but this may be of interest. Shortly before he died, my late father had our Chummy's engine re-built. It was fitted for the last few runs he ever did in the car, covering only a few hundred miles. Since then, I've been running the car, and it ran perfectly until last year when it mysteriously "went sick". After trying all the usual things, I decided to take the cylinder head off to check the condition of the valves and seats. However, I discovered that the nuts were barely more than 'finger tight' and the head lifted off with zero effort! There were signs of leakage past the gasket, which was new when the engine was reassembled. I re-fitted the head with a brand new gasket, all clean and dry apart from a trace of blue Hylomar around the water jacket holes. I used an accurate low-range Britool torque wrench and stage-tightened the nuts to 20lbs in the correct sequence. After a single heat cycle, I re-torqued the nuts and they all moved a good half a flat. I subsequently re-torqued the nuts a further two more times over a number of heat cycles before the nuts finally stopped moving. So I have concluded that these modern gaskets have a lot more 'give' in them than gaskets of old, and need multiple re-torques before they become fully compacted. I believe this is why the previous gasket "failed", simply because it hadn't been re-torqued sufficiently.