Bronze age: Racers have several valve
seat options. Copper seats are the best.
SHOULD I DO MY HEAD?
My dealer says that I should have
my cylinder head ported and have
copper valve seats installed. It seems
expensive. Is it worth it?
Having the full-race treatment
done to your cylinder head can
produce as much as a 4-horsepower
difference over a worn cylinder head.
A rebuilt cylinder head makes more
horsepower because the porting
improves air velocity and the new
valve seats increase durability and
provide a better compression seal.
A four-stroke engine depends on
the integrity of its valves. The
biggest cause of valve wear is
contamination from dirt that is
sucked through a dirty filter. The
cleaner your air filter, the longer your
stock valves will last. On a well
maintained stock bike, the valves
should last approximately 40 hours
before you need to be concerned.
Ryan Villopoto gets five hours out
of the valves on a practice bike. His
race bike gets fresh valves and fresh
valve seats for every race.
Valve wear is most noticeable on
the valve’s mushroom-shaped head.
The contact face (the sealing edge
of the valve head) will get cupped
where it mates against the valve
seat. When the valve face gets
cupped, it changes the dynamics of
its interface against the valve seat.
The more the valve cups, the quicker
the valve seat wears and the more
dramatic the power loss.
The valve face never actually
contacts the aluminum cylinder head
because of the valve seats. The valve
seats are typically composite iron
rings that are countersunk into the
combustion dome of the cylinder
head. The valve-seat ring is 5mm
thick. To make the stock cylinder
head last longer, a race shop can
recut the valve seats to offer a new
surface for the valve head to seal
against. Every time a valve job is
done using the stock iron valve
seats, it will increase valve wear
because of work-hardening of
the metal ring.
The solution to this problem is to
replace the iron valve seats with
copper valve seats—typically
Ampco 45 or copper/beryllium. The
copper-based materials are softer than
the stock iron seat, but the beryllium
alloy makes them harder so they can
stay cooler. The combination of copper
and beryllium allows the valves to
shed heat faster and seat quicker for
a superior seal. Valve and valve-seat
wear are also substantially reduced.
As a rule, copper-based metals wick
heat away from the valves better than
iron. Wicking the heat away from the
valves helps the engine retain horsepower. Engines make their maximum
peak horsepower after just a few
minutes of running, and then the
power tapers off. All things being
equal, the copper-based material won’t
make the horsepower go up, but it
will make the drop less dramatic.
As for the cost, it is a push. It
costs the same to upgrade to copper
valve seats as to buy a brand-new
cylinder head. Since it still takes
valves and springs to complete both
jobs, it makes more sense to modify
the valve seats than to swap out to
a new stock head, especially if the
old head has already been ported.
In the long run, changing the valve
seats saves money, especially if you
plan to keep the bike for a long time.
Subsequent valve jobs can be done
without replacing the copper seats.
Copper valve seats have to be
machined to interface with the shape
of the valve head. L.A. Sleeve uses
a $100,000 Newen CNC machine to
do its valve work. NASCAR teams
use the same machine to put copper
valve seats in their race engines. The
Newen machine shapes the angle of
the valve’s sealing ring. Most common
valve seats are cut at 30 degrees, then
45 degrees and finally at a 60-degree
angle. This is called a “three-angle
valve job.” Some performance shops
use two more angles following the
60-degree angle to make a five-angle
valve job. L.A. Sleeve rolls their five
angle cuts into a radius instead of
distinct angles. They claim better
flow numbers with the five-angle
The final step is to monitor the
valve-seat height. It’s measured
between the top of the valve stem
and the cylinder head deck. Each
valve job removes material from the
seat, which raises the stem end of
the valve. While this change has no
effect on compression, it relaxes the
valve-spring tension. Thus, if you plan
to keep the bike a while, it is worth
it to have copper valve seats put in
Spin doctor: New steering head
bearings are easy to change.
MY YZ250 WON’T TURN
My Yamaha YZ250 won’t turn.
I don’t mean that it won’t turn
corners. I mean that the front end
feels like it is stuck in place. If I
apply pressure to make it turn, it
will, but it isn’t right. I don’t have a
lot of money, so please tell me there
is an easy fix.
Your steering head bearings
might have galled or brindled, but
if we were betting men, we’d bet
that they have corroded from lack
of grease. If you are lucky, you can
re-grease them and they will start
working again, but most likely you
will need new Yamaha steering-head
bearings and races. The races come
with the new bearings and are
matched to work perfectly. Don’t
try to save work by not replacing
the old races. Just use a long punch
and work your way around them to
remove them from the frame, and
then use the old race as a punch to
tap the new race in place.
Italian bred: Boutique builder TM isn’t
bringing any bikes into the USA this year.
YOU MISSED MY FAVORITE
Why did you leave TM out of your
2014 shootouts? TM deserves more
respect from MXA.
We did not disrespect TM, but we
can’t test what doesn’t exist. TM did
not import any 2014 models to the
United States. TM USA says that
the exchange rate is so unfavorable
between the dollar and Euro that they
will not bring any bikes in until 2015.