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Gents,
I need to put you all right on this one. It's very important to get the valve lash correct. If it's too tight, the exhaust and (to some extent) the inlet valves will increase in length when exposed to high combustion temperatures and particularly if running WOT for a long period of time. If there is insufficient tappet clearance, the valve stem length will increase and take up all the lash and then the valves will never touch their seats. The motor will then lose compression, start back firing and also very quickly burn away the exhaust valve seats - game over. The correct valve lash for a ford FE with iron heads and block is:
0.025" hot.
This can be reduced by 0.008" for aluminium heads or 0.012" for aluminium block and heads.
Be warned, don't play around with valve lash thinking that it will affect performance - it won't, you'll just wreck your engine!
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