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VALVE SEAT CONVERSIONS FOR UNLEADED PETROL

Jim Whyman, Secretary

 

There have been a few reports of valve failures on

cylinder heads that have recently been converted with

hardened valve seat inset for use with unleaded petrol.

The FBHVC's Fuels Committee's specialist, Dr Matthew

Vincent, made the following observations, and car clubs

.are invited to pass these on to their members:

Fitting valve seat inserts to older engines can lead to

difficulties if care is not taken with choice of insert

material. When the head is machined and an insert fitted,

a thermal break is introduced. The chief means for exhaust

valve cooling is through the seat, so when a thermal break

is introduced, exhaust valve temperatures increase.

Exhaust valve failure in heads with inserts is thus more

likely. To counter this, the best inserts are

manufactured using sintered powder metallurgy

techniques. Heavy doses of copper can be introduced into

the seat to improve heat transfer and thus counteract the

tendency to overheat.
 

It is also known that older cars frequently run

significantly hotter as a result of wear and cooling system

inefficiencies. These problems render such vehicles more

likely to suffer valve burning or valve seat recession type

failures. Consequently, it makes sense to check cooling

systems and general engine health before spending money

on an 'unleaded' conversion. It is also important to check

that the conversion uses sintered metal inserts with good

heat transfer characteristics.

FBHVC