Kawasaki KIPS Powervalve Improvement

Applicability
This 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.

The Problem
I 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:
Kawasaki 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.
The 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:
The 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 out-of-sync positions.

The Solution??
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.
If 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:
Using 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.
You 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.
When 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.
I 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.

Servicing
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 necessary.
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.

Follow-up
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.
See this thread for Canadian Dave's complementary method of compensating for wear in the lower spindle bushing too.
Any improvements or viable alternatives will be posted on this page. Please contact me if you have any.

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