Leaded Fuel

["Hearnden,Jim,J,BGOI6 HEARNDJ M" <HEARNDJ@xxxxxxxxxxxxxxxxxxxx>]

Paul writes:-

>A paper I recently read claimed that after an engine had been run on leaded
>fuel for only a few thousand miles there was no significant difference in=
>valve-seat recession whether it was run with leaded or unleaded fuel from
>then on. 

Unfortunately it isn't as easy as that....It seems that leaded only engines
have a memory and valve seat recession only occurs after a lack of lead for
some time. This time is also dependant on how hard the engine is driven 
generally it is much worse on hard driven engines.
Most older alloy headed engines have less problems because they
automatically have steel inserts in the head.
The BMC A series is one of the worse in the UK because the cast iron used is
very susceptible to recession.
This is estimated to affect 6-8 million cars in the UK  and the black magic
additive manufacturers are all coming 
out of the woodwork, most of which when tested are found not to work..... 

Regards

Jim
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