Valve lapping info:
A gain in midrange HP, or "torque" is often better than top-end gains.
Besides the obvious gain of more initial speed on the "dragrace" out of
turns, the advantage is really due to the drafting factor.
If your bike is equal to your competitor coming out of turns, but faster on
top-end, your competitor can easily equalize the advantage by drafting.
Then it becomes a braking battle, which can end up slowing your lap times,
and effectively turn your advantage to zero. But, if you can pull some extra
bikelengths out of the turns, then the draft is broken, and as long as your
bike is at least equal on top end, the other guy has a much harder time
getting close enough to challenge you on the brakes.
That's why I like smaller ports ... the biggest advantage is often that they
gain on top, and midrange. If they gain on mid, without losing top-end, your
still getting the bulk of the advantage...
If you get the valves to seal perfectly, the bike will make the best
possible power out of corners. This is because a little leak is a lot !! The
high combustion pressure will find any leak, so you've got to get them
perfect. This is the secret to getting a good drive out of corners, and a
lot of tuners don't realize how important this is. When you've got slightly
leaking valves, it often doesn't show up on the peak dyno readings.
But...
When you're at lower rpm's exiting corners there is more time for the
pressure to leak out than at max revs, so the real power loss is in poor
acceleration !!!
The best way to do a valve job is to use very fine (400 & 600 grit) valve
lapping compounds, and lap in the valves. Don't re-cut the seats to radius
them or add extra angles. The stock angles flow the best !!! The lapping
compound I use is Clover brand, and the fine grades that I recommend
are available through MSC Industrial Supply -- phone number
(800-645-7270). This isn't the same as the Clover lapping compounds
commonly available, as they are much finer. Unfortunately, this product
is only available in large cans, which is more than the average enthusiast
will ever need -- but it's really not that expensive once you discover that
this is by far the cheapest power gain money can buy.
Especially don't be tempted to use the rough lapping compounds (usually
packaged in tubes) which are commonly available at auto supply stores.
Although they will work quickly, they leave deep grooves in the valve seat,
and wear into the hardened surface layer of the valve. Both of these problems
will soon lead to compression leakage after the engine has run a while.
400 grit lapping compound:
(1lb. can $16.00) part # 00274001
600 grit lapping compound:
(1lb. can $25.00) part # 00276006
1200 grit lapping compound:
(1lb. can $40.00) part # 00265801
{Note: the 1200 grit is much more expensive, and if you decide it's too
much, just skip this step. The 400 & 600 are the most important}
Rolite Polishing Compound -- I tried to find a website for it, but no luck.
Anyhow, it should be available in hardware stores. The last time I bought
it, it came in a silver tube with blue writing on it.
Update: here is a place that sells the Clover compound in 4 oz. quantities
for anyone who doesn't want a 1lb. can.
http://www.utsupply.com/viewprodtable.asp?CategoryIDSS=30
The Lapping Process -- Start with the coarser 400 grit compound, and use
only small "dots" of lapping compound about 1mm apart around the sealing
face of the valve. (Using any extra will just make more of a mess.) Be very
careful not to get any on the valve stem, or into the valve guides -- as
valve stem and guide wear is something that you want to avoid at all costs
!!) The action is to rotate the lapping suction stick back and forth about 8
times until the grinding sound and feel goes away, then without removing the
lapping stick, just lift the valve slightly and tap the valve on the seat 2
times, then go back to rotating about 8 more times. (The tapping brings some
of the "grit" back onto the seat, and the grinding effect becomes effective again.)
After about 3 of these cycles, the grit in the compound is done. Clean the valve
and seat off with paper towel.
After lapping the valve with the 400 grit, use 600 grit in the same way to
smooth out the small grooves caused by the 400 grit. Never use 400 grit
twice in a row, or the grooves get too deep to smooth out with the 600 grit. The
way to do it is 400-600-400-600 etc... Check for leaks as outlined below after each
400-600 "lapping cycle" until the valves are 100% sealed. (I've found that it usually
takes two or three 400-600 cycles, but always check for leaks after each cycle,
since some valves will lap in after just 1
cycle. The idea is to lap the valves as little as possible and still get a
perfect seal. Excess lapping will only sink the valve seat and lower the
compression ratio.
Checking For The Perfect Seal -- I do this as I'm working on each valve, and then
mark the valves as they pass this test. Be sure not to mix up the
valves, because each valve will only seal correctly with the seat it's been
lapped to !! Set the head on the bench with the combustion chamber side up. With
the seat and valve absolutely clean, install the valve in the head,
without assembling the springs. Check the seal by setting a super bright
light on the combustion chamber side, then look into the port. You want
total darkness, so in multi valve heads, put in all the valves for that
port. Once your eye adjusts to the dark, rotate the valve and you can see if there
are any light leaks. Light from the "blind" side will reflect off the
valve stem. You'll be surprised at how many professional valve jobs leak
when tested this way !!! Note: the area around the valves and seats must be cleaned
of carbon, or it will block the light. It's best to do this before
you begin the lapping process.
Once the valve is sealed, I use an extremely fine (1200 grit) lapping
compound and lap the valve in using one lapping cycle to get rid of the 600
grit grooves. (Almost impossible to see, but even at a microscopic level,
the valve will still leak under the extreme pressure of combustion.)
With the 1200 grit lapping compound, the finish effect is almost complete,
only there is still a gray band left on the valves and seat. For the final
step, finish with 1 lapping using metal polish to actually polish the valve
and seat. This is done for 2 reasons -- to make the metal to metal contact
as perfect as possible, and it also removes any traces of the abrasiveness
of the lapping compound. The brand I recommend is Rolite. This product isn't
like the chemical type for polishing silverware, but rather the type that's more
like toothpaste, with a extremely fine grit to it.
You only need to use the 1200 once and the Rolite once. (Also, you won't
have to recheck the seal, as with the 400 & 600 grit lapping cycles since
these compounds are so fine.) Using these last 2 compounds might seem like
a waste of time, but it's all about doing an outstanding job, and one where the
power will last as long as possible.
Thoroughly clean the head and valves, and assemble them with the utmost
care in a super clean workbench environment. All it takes is 1 grain of dirt or
grit between the assembled parts, and all that work will be ruined the first time
the engine is started.
As you can imagine, I ALWAYS recommend using an air filter, since 1 lap
around the racetrack with open intakes will suck in enough dust to un-do the
polished finish on the valves.
Be sure to check all the valves for "cupping" of the sealing area. If the
valve looks like it's worn, even a small amount, you should replace it. For
example, most older Yamaha (FZR600-FZR 400-FZR750) valves I've seen need
to be replaced.
The good news is, once the valve seal is perfect, they will last a lot
longer. The heat from the leaking valves is what makes them leak worse and
worse, until they eventually wear out. Surprisingly, all the engines I've
ever worked on leaked ... brand new and straight off the assembly line !!
Keep everything in the engine super clean, I can't stress that enough !!! Be
extra careful with the lapping compound, as it can do serious damage if it
gets in the guides, or anywhere else in the engine.
(Courtesy of Pat McGivern (Motoman))