Lost the powervalve cheerio-thing on my bike a few weeks ago.
88/89 KX250 and I imagine the early 90s ones/KDX250 etc...
I didn't know it was gone for a ride or two, but bike was acting funny, and I eventually spotted the issue after removing the little plastic cover. Looks like the outer e-clip popped off, and the thing must've flung off somewhere. The rubber boot on my powervalve cover setup is torn up, so it wasn't captured for me.
Anyway, AFAIK, this part is not sold anymore. I looked for something close enough in the machine-parts world and then finally found something to work with in the RC-boat world. A prop-shaft drive-flange.
https://www.amazon.com/dp/B07R9JHCBW?ref=ppx_yo2ov_dt_b_product_details&th=1I wrote it all up in a review on Amazon... the title is 'Not the use intended, but it worked great'.
If there's a real replacement out there, I'd love to know about it. This thing I made has worked for several weeks and 2-dozen rides, but I'd still prefer the OEM part.
These things from Amazon are metal collar-bushing sorts-of-dudes... I don't know what the real name is... a flange I guess. Anyway, they have a 5mm id already, and has one 'side' in place to start with. The 5mm id is tight on the pv-shaft.. you'll have to ream it out a smidge.
Steps to make your own:
Tools: a mig welder, or a buddy with one. grinder or a set of flat-files. metric calipers. vise or some way to clamp these small parts... vise-grips would prob work too... be creative. Assorted small parts/hand-tools dang near anyone with an old dirtbike will have lying around. Safety gear for grinding.
0) I believe the original part's overall width is on the order of 8mm. You need to work -to- this width, so to speak. I believe the inner-width between the flanges is 4mm. The overall diameter is about 17mm. I measured a 2nd one of these I have on another bike.
1) file/grind down the inner 'hub' part such that the width of the whole part is now about 6mm (we're leaving about 2mm to add on a 2nd 'flange'). The finished product needs to be able to fit on the shaft with both e-clips holding it in. Test-fit often to make sure you're on-track. I had to run a 5mm drill bit through the hole in the middle and work it a smidge to add some free-play so it'll spin on the pv-shaft.
2) find a nice flat steel washer with a 5mm hole in it (and an OD on the order of 17mm, you can grind down to fit later if need be) and weld this to the hub that you just ground down. Again, try to ensure overall width for the part is 8mm. The reduction to overall width in step 1 is to provide for a 'well' to push tack welds into. This will initially close up the 5mm bore.. you can drill that out later.
--- Its ok if you are initially at a point where it's too-wide... you can grind it all down later. Don't try too hard to make it exactly-sized right off the bat---
3) Set the spacing between these 'wheels' to be 4mm. its probably really 4.0something.. I don't know that exact measurement. A later step is to file these flanges to get good clearance. So, whatever you need to do to fixture this up to achieve this, I used some feeler gauges on each 'side' of the middle just laid in-between the washer and the 'base'. Try to make the new washer parallel to the existing flange. I use welding magnets to hold things down to my welding table.. but a vise would surely work.
4) tack-weld in a spot or two... check your work... measure and check for parallel. It doesn't have to be 100% perfect, but try not to make it really out of whack. Add more tacks to get a complete weld. There's 4 in the set from Amazon, you have some spares if needed. Turn the heat and wire-speed down and sneak up on it.. don't blast it on full-juice and turn it into a molten glob.
5) the weld-beads will make the overall width wider than 8mm.. so file or grind them down. This may wind up grinding through your existing tacks... just be patient and re-do as needed, you'll eventually stick them together.
6) the overall diameter of the flange on the Amazon part is too large... you'll need to take it down a couple of mm. I found no great way to do this other than putting it on a screwdriver, fix-it in place with two small hose-clamps but w/room so it'll spin, then ran it against a grinding wheel with some angle so that the grinder both spun the part and ground it down. Ugly, horribly inefficient. Very likely deadly. Wear all the protection (I wear a full-face shield and a leather apron and gauntlets) this is hair-brain stuff.. no real machinist would do this. If you're just super offended that this was even suggested, I'm sorry you're offended. I do a lot of unsafe stuff that would make you uncomfortable... like, riding dirtbikes at speed in the woods
I don't have machine tools, so I gotta make-do.
---The OD you wind up with doesn't have to be 17mm like OEM... mine was prob 18.5'ish.. there's some room in there for it to be slightly over-large. Test-fit.. you're just looking to make sure the nub on the pv-arm registers well and that the spool-wheels don't rub on the shoulders of that pv-arm.---
7) lather, rinse, repeat until you've got something that fits between those e-clips and that the little arm will register into w/out sticking. This spool will spin on the shaft, so make sure there are no tight-spots with the little nub on the arm.. spin this spool and check that the 'nub' doesn't get stuck. If it does, mark that spot, remove spool, and take a flat-file to the area where it was sticking.
There is no doubt that this solution is way less accurate than the OEM part. Every ounce of slop or mis-fittment you wind up with will affect how the powervalve 'comes on'. People pay big money to port cylinders where they move a port 1.2mm or whatever. And we're probably messing that all up. I'm not suggesting anyone do this on their race bike. I ride single-track trails, I'm not a racer and no winnings/money is at stake that I would use to feed the family.
I went to this solution b/c I could not find a powervalve cheerio anywhere and I figure 'an underperforming part is still better than nothing'.
I saw a listing on ebay for something that might be a replacement, but the part-numbers the guy listed put it for a mid-90s 125, which is different than what I needed. I'd take the other one I have to a machinist to fab up, but I can imagine that would cost, what.. couple of hundred bucks in his time/effort?.. meh.. this one I cobbled-up works well enough for me. I spent maybe an hour b/c I had to figure out what to do from scratch.
