At 02:07 PM 6/9/98 -0500, Bill Eastman wrote:
>.....
>So, are these wonder valves worth it?
If you drive 2500 miles a year, probably not. If you drive 10,000 miles a
year, or you drive hard and hot on a regular basis, most likely yes.
I drive my MGA long distances at fairly high speeds in hot weather, tow a
small trailer on a regular basis, and autocross regularly. And in this day
and age we are limited exclusively to unleaded gasoline here in the US.
For several years I used standard exhaust valves, and they would make it a
year or two between touch ups. For me that was about 20,000 to 25,000
miles. But then I was being particular and getting them touched up at the
first signs of low compression. A few years ago I installed stellite
exhaust valves, and to my delight they made it 45,000 miles and were still
functional, although moderately worn at that point. Looks to me like the
stellite exhaust valves will last at least twice as long, and the
difference in cost is more than offset by the savings in labor by negating
every second valve job. But then I average about 20,000 miles a year of
serious driving, so YMMV. And I figure the average driver will get more
miles out of a valve job than I do.
>Should I lap them into the seats or will that remove the platinum- er
stellite coating? Are these valve regrindable or will I have more smelly
paperweights when I do put in hardened seats?
Beauty is only skin deep, but stellite goes all the way to the core.
Stellite is an alloy, not a coating. They can be reground the same as any
other valves.
>the exhaust valve seats are fine now with no recession so I hope to put
that expense off until the bank account recovers ....
Hardened steel valve seats are the cat's meow. I now have over 100,000
miles on a set of hard seats, they have outlasted a couple of sets of
valves, and they still look like the day they were installed. I'm
absolutely positive that they wlll outlast me.
However, if your original valve seats are currently in good condition and
showing little or no recession, they will probably last at least as long as
a set of standard valves, and possibly even as long as the stellite exhaust
valves. With these conditions you might as well save your money now and go
for the hard seats the next time around, if there ever is a next time.
Without hard seats you may expect to encounter a little recession, so you
would want to check/adjust the valve clearances occasionally. If the
clearances get too small you will start burning valves.
If the shiny seating surfaces in the valve seats are growing to a little on
the wide side, you should consider the marginal extra expense of doing a
three angle valve job on the seats to narrow the mating surface back to
factory specs. If the mating surface is too wide there will be
insufficient presure from the springs (force per unit area), and the mating
surfaces will accumulate carbon buildup. Eventually the carbon flakes off
a bit leaving little passages where the hot exhaust gas can go whistling
through under pressure, which will erode the metal surfaces and lead to
early demise of both the valves and seats.
What you do and how much you spend on a valve job is a judgement call,
should be based on how much and how hard you drive the car, and may be
affected by how rich or poor you feel this month or this year. Some
expenses can be delayed or avoided. Some expenses should not be delayed
and may not be avoidable. The more you learn, the better the world.
Barney Gaylord
1958 MGA with an attitude
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