Message 5299
http://autos.groups.yahoo.com/group/afm250p/message/5299

I have been dealing with Web Cam for several years now, and I must say they
don't know what the hell they are talking about! It is true, in most cases,
that valve float does cause rapid deterioration to the valves. No argument
there. However, if you look at the seat widths on the stock Kawasaki valve
seast (all models), you will find something very interesting. The intake
seats are about .025 wide, and the exhaust around .030. These seats are very
nicely designed for maoximum air flow at low valve lifts. These valve seats
are CRAPPY for longevity. The seats cannot transfer enough heat in the give
amount of time that the valve spends sitting down (on it's seat). There are
only 2 ways to increase heat transfer, time or surface area. Since we don't
want to lengthen the time the valve sits on it's laurels, cause that would
effect horsepower on a race engine, we obviously need to increase the surface
area. I have spent consdierable time designing a valve seat profile that has
a larger surface are, and ZERO loss of low lift airflow. I think my dyno
numbers have proven that.

I will admit, though, if you are talking to Web, than you are considering (or
already have) aftermarket cams. If that is the case, I would say that Web's
description hoolds accurate. Esspecially since they have not proven to
understand that you need to make moderate, incrimental changes to cams in a
small motor such as these. The cams I had them grind to my specs (which they
were way off on that) absolutely did not work in an EX-250. And, the cams
they normally sell for a VTR-250 are a flat out Joke! Just ask Ginny :-))

I am still experimenting with cams. But, in the mean time, I would stay away
from aftermarket cams in the EX, and even still be wary of aftermarket cams
in the VTR.

That's my opinion. I own it. And I take full responsability for it.

Mike Norman
G-Force Performance Center

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Message 5287
 I have heard (over and over) to set the valves as you have
recommended. However, I have several issues about this theory. First, let's
take the valve adjustment specs and discover why they are there. Forgive me,
I don't have a book in front of me, so I will use industry standards for
comparison. I believe that Kawasaki uses a +/- .02mm variance on their valve
specs. So, with a nominal clearance of .10mm intake, the range would be
.08mm to .12mm. .02mm is less than .0008". The motorcycles that we race are
designed to be manufactured in mass quantities, therefore have to have a
range of acceptable tolerances. They are also desinged to be maintained in a
dealership environment, where the mechanic is given a "flag" time to do the
job. The valve clearance range that is given is so that a dealership
mechanic can slam a feeler gauge in there and say, "go, or no-go". If it is
out of spec, s/he can quickly adjsut it in to spec, since their is a
reasonable range of acceptable clearance.

Now let's look at the range of acceptable clearance. Have you ever
opened a micrometer, or caliper to .0008"? You can barely see it! I would
love for somebody to show me that they have gained horsepower from an
additional .0008" valve lift, or an extra .25 degree of duration. Or, at
least enough horsepower to "feel" the difference. The valves are going
through their motions of opening and closing at a rate of 83 to 116 times per
second. I want you to picture in your mind what air/fuel would look like
moving, stopping, moving, stopping...at that rate. Can you picture and extra
.0008" of lift, or an extra .25 degrees of duration making a difference?

Here's my philosophy on the matter. The valve clearances are given to
maintain some clearance between the valve stem and the rocker, so that the
valve will actually close when it is supposed to be closed. As anything
heats up, it expands. Valves grow in length, therefore needing extra
clearance when cold. Exhaust valves will obviously grow more, since they are
exposed to around 1200 to 1800 degrees of hot gasses flowing over them while
that valve is open. Infact, they are glowing red while they are open. As
the valve closes, the heat needs to transfer to the head as quickly as
possible, because they only stay closed as little as 116th of a second.

So, if the theory is correct, than a looser valve clearance is
required on the exhaust side to first of all leave room for extra growth on a
race engine that sees more heat than the engineers had anticipated, and
second, give the valve a little more cooling time on the seat (less duration,
by less contact with the cam during it's ramp cycle). In theory, it sounds
great. In reality, I would love for someone to show me it's true. A wider
valve seat face will transfer more heat faster. However, I do recommend that
exhaust valves do stay set to the looser side of the clearance range.

So, again, if the theory is correct, than the intake would actually
not require as much clearance because it has a cooling effect from the intake
charge passing over the valves as they are open. The manufacturer has
already taken this in to account, that's why intake clearances are usually
less than exhaust clearances. Also, if you were to set the clearances
tighter (in theory) you would gain more lift at the maximim valve lift, and
more duration because the valve follows more closely to the cam profile.
Tighter clearances are fine for people who want to maintain their valves on a
per-race basis. But, is it worth it? tighter valves on an EX-250 opens the
risk of valve damage to the already soft Kawasaki valves. Setting the valve
clearances to the middle of the spec can help to keep the adjustment
intervals down, and the longevity of the valve up. So, can the right width
valve seat.

So, your "friends" may be right in theory. It sounds great. But, I
am highly suspect of the benefits vs. the risks. My recommendation would be
to set the intakes towards the middle od the range, and the exhausts towards
the looser side of the range. I think the theory is a waste of time to try
to adhere to. It may work on a big-block Chevy, where the range is wider, so
the difference is bigger. Also, picture a valve that is the diameter of our
pistons being opened an additional .003" of an inch. Of course you will see
the difference. The area of valve opening (known as the "curtain") is much
larger due to the sizes we're talking about. I call it "Barnyard Chevy
Mentality". You gotta keep things in perspective here.

I hope I have shed enough light on this subject for you.

Mike Norman
G-Force Performance Center

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