From: Dave Baker
Subject: Re: burned valve
Date: 28 Apr 1999 10:06:47 GMT
>From: firstname.lastname@example.org (PLAlbrecht)
>>More information, please, Pete. Did the engine have hardened seats, or
>>stellite or stainless valves? Any of these will prevent the valve seat
>>failure associated with older engines.
>Ordinary modern ("hardened," compared to the Good Old Days) seats. Don't know
>valve material but FWIW they're magnetic, fairly ordinary and made by Alfred
Then it is not surprising that the engine did not suffer from seat recession
with unleaded. Recession primarily affects exhaust seats in cast iron heads.
Any head with steel inserts will be fairly immune although the quality of the
insert material is an issue.
I have studied seat recession for many years on both road and race engines and
read widely on the subject both on and off the web. The consensus of my opinion
FWIW is as follows.
Standard valve materials for modern engines are usually magnetic 1 piece EN52B
type material for inlets and 2 piece friction welded EN52B stems and non
magnetic 21/4N type material for heads. Only the exhaust is of concern for
unleaded issues in most cases and the standard 21/4N material is adequate. This
material is required to withstand the high valve temperatures generated in
engines regardless of fuel type. It is very rare to find a modern engine with
magnetic head material on exhaust valves and only in such a case would an
improved material be required for unleaded use.
As an aside are you absolutely sure that the exhaust valves you refer to were
also 1 piece magnetic?
There is no apparent relationship between guide material and suitability for
unleaded use. Cast iron guides are perfectly serviceable and the recommendation
of many engineering shops to change to bronze guides is a nonsense in my
opinion. Many modern engines designed to run unleaded still use iron guides
(e.g. Ford CVH) with no problems. In my own opinion, cast iron is actually a
much better guide material than the grades of bronze used in most modern
engines. Guide wear on engines with bronze guides such as VW Golf, Peugot 205
etc is far higher than on engines with iron guides such as CVH. Heavy duty
diesel truck engines designed for very high mileage still normally use iron
Recession primarily affects cast iron exhaust seats. Any aluminium head will
have steel inserts by definition and even on older engines there will be a high
tolerance to unleaded. The ideal insert material is a high chrome steel treated
to Rockwell 45 or over.
Inlet seats are rarely an issue except on very highly stressed race engines.
(There are a very few rare engines with aluminium heads and cast iron inserts.
The Lancia Gamma flat 4 engine and the 2.5 litre V8 Daimler Dart SP 250 engine
are 2 that I have encountered so far. No post 1960 high volume engine uses
anything other than steel of some type or other AFAIK)
Recession accelerates markedly with sustained high rpm and high load use and
consequent high chamber temperatures. Even cast iron seats will endure unleaded
for considerable mileages in road use if rpms and loads are not excessive. In
race use it 'may' be necessary to fit inlet seat inserts as well but even in
these conditions it would be rare to find inlet problems.
If your engine has aluminium heads and 21/4N exhaust head material then fill it
up and drive it. With cast iron heads only the exhaust seat inserts will need
to be changed in the overwhelming majority of cases. Standard valve and guide
material will be fine unless exhaust valves do not have 21/4N type heads. The
TRW catalogue indicates valve material for the valves listed and is a handy
Dave Baker at Puma Race Engines (London - England) - specialist flow
development and engine work. .