>From: "Graham Stretch" <technical@iwnet.screaming.net>
>The export models of some of our cars headed for some markets may have had
>hardened valve seats fitted. The home market cars did not have valve seat
>inserts fitted, they use the cast iron of the head to machine into valve
>seats. the only exceptions to this are the cars fitted with the slant four
>engines as these had alloy heads with valve seat inserts.
>
>> The panic we've seen about only 'soft' valved cars being built up to
>> 1988 is something of a myth. Certain cars are affected to this date but
>> many are not. There is ample evidence that the main supplier of valve
>> seats in the UK (a company named Brico) was supplying 'hard' seats over
>> thirty years ago to manufacturers shipping cars to North America. In
>> manufacturing terms, there was little, if anything, to be gained by
>> specifying different types of seat dependent on market destination. This
>> is why a substantial number of TR and Spitfire owners on both sides of
>> the Atlantic have reported no problems switching from leaded to
>> unleaded. The same goes for Herald Vitesse Dolly and the 1300/1500
>> FWD's. All these cars were fitted with hardened seats. I've heard much
>> the same reports from Rover P6 users and a good many MG and Sunbeam
>> owners too. I guess the only people likely to have VSR problems are
>> those owners who have had a major head overhaul but found they'd been
>> tucked up with 'soft' valve seats on the grounds of cost from an
>> unscrupulous workshop or truly do have a soft valved car.
One thing that generally is true for British cars is that the heads
for export models are generally the same as the home models. There are
some cases where that's not true, but even in those cases the valvegear is
generally identical. I found highly amusing the "unleaded" conversion head
jobs offered for $$$ for Rover 3500's/etc (3.5l/etc Al V8) - since their
heads are aluminum with inserts already, and the inserts are easily up to
handling unleaded (EASILY). This is confirmed by an engine designer who
worked on them for Rover.
This, shall I say, "hysteria" has been going on in Britain for some
time now. We in the US converted to unleaded decades ago. I've never ran
into a US owner of a british car with serious VSR problems. My TR6 ('70,
long before unleaded was an issue in the US) has 170K miles on it with no
recession problems. It's been using unleaded solely for the last 10-12
years. Even if it had a slight amount of additional recession, the worst
is that you need to adjust clearances a bit more often, and eventually
(maybe) you might need to install seats when a valve job is done.
Recession doesn't happen suddenly (except in 1000-hour full-load tests).
If you see continual adjustments needed to the valve(s) (due to closing
gaps) over a series of years, then you might want to consider going to
an additive or getting a head job done with inserts. Maybe. Certainly
nothing to panic about.
Don't forget that the tests that are done are using the known worst
head for recession, using a load regimen that simulates a LOT of hard
miles. Given most of our (old) cars get 2000-5000 miles per year (with
some exceptions), even with a worst-case head, it might take 5-10 years of
use, maybe 15, to develop even a moderate amount of recession.
There are some "home-market" cars that manufacturers skimped on and
didn't harden the seats (yes, I believe cast-iron seats are normally
hardened, I think via induction). A few of those will have recession.
Here in the US, lots and lots of American engines had cast-iron
seats from the pre-unleaded days. Most of them had little or no problems
switching to unleaded. There is no big market for unleaded conversions
(some, just not very large - it's probably bigger in farm equipment).
The only big issue is getting the right octane for some of the late-60's/
early 70's muscle-cars.
--
Randell Jesup, Worldgate Communications, ex-Scala, ex-Amiga OS team ('88-94)
rjesup@wgate.com
CDA II has been passed and signed, sigh. The lawsuit has been filed. Please
support the organizations fighting it - ACLU, EFF, CDT, etc.
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