Dear Duplicate Thread Police, I realise this thread is duplicated from the Pug forum but thought it is important enough to be in both forums to reach all those interested. If the moderator or forum owner has a problem, please delete whichever posting is considered inappropriate. Now to the message......

Let's see if we can finalise once and for all the discussion about valve seats and their suitability for unleaded.

These details are for USA market cars.

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Exhaust valve seat P/N 0227.16 to suit XN1 and XNA up to 2.570.000.

Exhaust valve seat from 2.570.001 P/N 0227.43 (1st repair oversize)

From vehicle 2.570.000, the US cars were fitted with a catalytic converter for unleaded fuel, therefore the change in valve seats can be considered to be hardened.

As a comparison, the exhaust valve seat for all Euro (and AUS) market cars (at least until 1983) was P/N 0227.16.

Therefore it can be summised that the exhaust valve seats of a 504 head are not suited for unleaded fuel, probably one of those things to get done when the head is off the car.

Now for 604.

Exhaust valve seat P/N is 0227.35 (1st oversize) for all 604's carb and injection USA, Euro and AUS(at least until 1983). From this it could be summised that the seats are hardened.