Kawasaki KIPS Powervalve Improvement
modification is based upon my 1991 Kawasaki KDX200. It should be relevant
for all similar models that use the older style of KIPS powervalve.
This would include 1989-1994 KDX200s. It might also be relevant for
the earlier air-cooled 200s ('86-'88) I'm not sure and
possibly some or all of the water-cooled KDX250s. 1995 and later KDX200s
and 220s use a different powervalve arrangement that does not seem to
suffer from the weakness of earlier versions.
noticed when overhauling my top end that the left side powervalve seems
to have a design weakness which probably contributes significantly to
its reputation for failing earlier and more frequently than the right-side
powervalve. The left valve suffers from prematurely worn and stripped
gear teeth. I believe that part of the reason for this is as follows:
uses the same removable top bearing collar on the left side as the two
on the right side (same part number for all three). This part has a
cutaway segment that, on the right side, locates the two collars together
and prevents them from rotating. However, on the left side the collar
is free to rotate, which it will do enthusiastically as age and vibration
take effect. The more the collar vibrates and rotates, the more it and
the powervalve bore are worn away, making the collar even freer to move
around. Eventually the clearance becomes quite sizeable.
wear clearance will compromise the intended alignment of the alloy powervalve
teeth with those of the steel shaft that drives it. This alone might
not quite be enough to break the tips of the alloy teeth, but unfortunately
the cutaway segment of the collar allows even more movement in the direction
of the missing segment because the collar lacks a complete circumference
there to meet the bore and maintain alignment. At some point an unhappy
coincidence will occur:
cutaway will sooner or later happen to be facing the back of the cylinder,
allowing the powervalve gear teeth maximum deflection away from
the steel actuator shaft. This will happen at a moment of stress when
the KIPS mechanism suddenly activates while perhaps the powervalve offers
some resistance because of normal crud and carbon build-up. The tips
of the soft alloy gear teeth now carry all this stress, and inevitably
chip and fail. As this scenario is repeated the tooth chipping becomes
so severe that the powervalve no longer turns or randomly jumps into
My idea is to reduce the clearance caused by vibration and wear, and
to prevent the cutaway from ever facing the rear, thus keeping the gear
teeth solidly engaged.
you are lucky enough to have machining facilities you could make up
a custom collar that has no cutaway notch and is a tighter fit in the
worn valve bore. Otherwise you might like to try my method:
an arc welder or car battery and jumper leads you can roughly build
up the outside of the alloy collar. You don't need a fancy TIG welder
to do this, just some scrap aluminium wire that will fit into the welding
handle or jumper clamp. You can salvage thick aluminium wire (thin rod)
from old TV antennas and stuff. You can even make enough "wire"
by cutting a thin strip of, say, eighth-inch or 3mm aluminium plate.
A couple of inches length should be plenty. Practice "welding"
on a piece of scrap aluminium first.
won't be able to sustain a good arc, but all you need is to deposit
some blobs of aluminium onto the surface of the collar that will take
up the clearance slack. Use a firm wire brush to remove any loose blobs,
and continue "welding" blobs around the outside of the collar.
Don't bother welding in the cutaway notch. Refer to my photo as a guide
for just how rough a job this can be.
Correctly oriented left-side collar showing
rough weld blobs
When you have enough firmly-adhered weld blobs
in place, the next step is to carefully file them down until they are
about the same thickness all around and will fit snugly into the valve
bore. File a bit, then test it and file some more. You want a fit that
is tight enough to discourage the collar from rotating, but loose enough
to allow it to be removed later (see notes below). I erred on the side
of snugness, tapping my collar home with an inverted socket and hammer.
you are ready to reassemble the powervalve, make sure that you line
the cutaway notch up with the front of the barrel (see photo) so that
all that extra metal you've just laid down will actually be pushing
the valve's gear teeth slightly in towards the steel shaft teeth. You
might end up with fractionally improved engagement compared with stock
instead of the sloppy engagement that causes the alloy teeth to chip.
coated the outside of the collar with a little silicone when reassembling
it too, as a way of further discouraging it from vibrating loose. This
might be especially helpful if your collar is not such a tight fit as
mine. Be careful, though: you don't want any excess silicone dropping
down onto the rotating parts below. Use it very sparingly.
When it comes time to remove this collar at your next service, you can
take advantage of a small amount of vertical leeway that the powervalve
has before it hits the steel actuating shaft. Grasp the protruding powervalve
spindle carefully with locking pliers and pull it up slightly to partially
dislodge the collar. You can then grab the collar itself and prise it
out. Try not to score the spindle too badly because even though the
top is not a critical bearing surface, you'll still want to be able
to slip it through the collar. File off any burrs on the spindle if
the above doesn't work, you probably have the collar in there pretty
tightly and might have to try drilling a couple of very small holes
part way into and on opposite sides of the collar's top surface. Insert
two self-tapping screws into the holes which can act as leverage points
for a screwdriver tip then work the collar up gradually.
After about a year I have torn my engine down again to discover that
the left powervalve not only has stripped teeth again but is snapped
into three pieces. The rough weld blobs that had held the collar so
firmly when installed have worn off from the effects of vibration, though
the collar was still correctly oriented thanks to silicone in the cutaway.
This is a somewhat disappointing result. I cannot imagine why the valve
shaft snapped twice. I will install another valve but if this happens
again I will give up in despair and silicone the valve permanently shut.
thread for Canadian Dave's complementary method of compensating
for wear in the lower spindle bushing too.
December 2012: Some hero in Russia has fabricated his own KIPS powervalves by hand, something I used to dream of doing myself. See the forum thread for a lengthy discussion (use Google to translate it if necessary) and more photos.
improvements or viable alternatives will be posted on this page. Please contact me if you have any.
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