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Powervalve woes?

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2007 KX250, all stock, about 8 hours on a replate from Langcourt with new OEM piston.  No mods, stock jetting.  When I got the cylinder from Langcourt I noticed that the main PV was sticking.  It would not open by turning the PV rod, no matter what I did.  If I let it close under it's on power, it would stick and not open back up.  I painstakingly dremelled and filed for hours to get it better.  I used whiteout on the PV to determine where it was sticking, and "shaved the port accordingly.  I thought I fixed that problem.  But now we're here.  The bike runs fine, but I definitely notice a change in engine character about an hour after riding.

At first start, the bike has a very "true" pull from top to bottom.  Very smooth, great sound, great power from 0 throttle up to power band where it explodes.  After about an hour of riding, I can tell the exhaust note goes raspy at times, and it looses LOTS of bottom end power.  It kind of happens incrementally.  The first time I noticed it, it almost sounds as if a pipe o-ring or something has come loose, the exhaust note goes from clear to raspy, and the pull on the bottom end slowly goes away...leaving a huge hit on top.  It would come and go with no clear indication of the cause.  After some time of continued riding, it got slightly worse, and would not go away.  Essentially going from a nice roll on clear powerband from bottom to top, to nothing on bottom, no mid range, and screaming on top.

So...does this sound like a PV problem?  I'm not sure how early the PV engages, but it seems as though it's sticking all the way until the motor is at like 20K rpms, and then letting go....let go of the gas, the PV smacks back closed, sticks, and repeats....no power until 20k when it finally breaks free.  That's what I picture in my mind, no idea if that's correct.  If I can replicate the PV stick once I take the cylinder off, should I send it somewhere to have some work done to fix the issue, or continue filing away?  Any other considerations?

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Is the small clock spring in place where the powervalve shaft comes out of the cylinder?  This little guy helps close the powervalve.  Yours is sticking open, which only starts to make power from like 8000 RPM on up.  If you are using high quality premix and everything is in good condition you really don't need it, but if you have any carbon or any other deposits in the power valve pocket it will act up.

Deposits can be left during the replating process.  This occurred on my KDX200 and caused the same issue you are having.  The actuator has a much easier time opening a sticky valve than it does trying to close one. 

I would be very conservative removing material other than what you know 100% to be either a carbon deposit or a burr in the plating.  You should not be removing any aluminum.  I have found abrasives debris left inside the nooks and crannies of replated cylinders before.  This stuff is left over from honing and the replaters don't always get all of it. 

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Check the spring. There have been a few failures over the years.

 

KIPS opens around 5,500 on that model I do believe then the main KIPS is around 6,000. I think it quits making power around 8,500 or so.

 

I helped a guy on a KDX one time that it turned out to have extra plating in the KIPS area on his KDX200. Yes, it was replated by Langcourt.

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Thanks guys, I'll definitely check the small spring and give an update.  That makes sense now that it would actually be sticking open.  At least it's not stuck closed! So hopefully I fixed that problem.

Yes, I was super super hesitant about removing any material from the main PV port, but when I disassembled then engine the first time I nearly couldn't get the thing out.  I had to pry, and use multiple expletives in order to do so, plus there really wasn't a lot of carbon build up.  I don't think it was close to enough to impede function and the PV opening was more a problem of super tight clearance in one small spot.  When I reassembled the PV was opening smoothly and not sticking.  Now that's said...I feel like I do remember a slight stick at the most open point too, but figured the spring and arm would take care of that.  Normally it's fine, but after more and more riding, it's become more noticeable.

If the spring is there and attached correctly, should I just order a new replacement and hope that fixes it?  I'm not 100% sure what actually makes the PV stop, is it just the mechanism that attaches to the rod inside the PV cover essentially bottoms out once it turns far enough?  Just need to see WHERE it's actually sticking and what's causing it to do so.

Also, I'm sure this is on here, but since I've got your attention....what's the best way to remove carbon from the actual PV?  I've used scotch brite and minor cleaners with limited success.  

I wasn't sure if Langcourt messed with the PV port, and was told that they didn't.  There were not any deposits that I could see so I probably did remove a tiny bit of aluminum.  I'm fine with that as long as it works.  My YZ cylinder should be back from MT this week, it did not go to Langcourt.

Edited by bcssrmz250

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Oven cleaner will eat aluminum if allowed to set for a while.

 

I would just open it up and see if the spring is broken before ordering another one. If you are ordering parts anyway, then go ahead and buy one as a replacement or future spare.

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I don't think there is anything wrong with the spring, but I haven't looked so I could easily be wrong.  I think the PV is sticking up top for some other reason.  If so I need to find out why and do some cleaning and possibly more filing.  Doesn't seem like it should be that difficult.  I do have to order some parts for another bike so I'll probably order another spring just in case.

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Welp...I was right, and wrong.  The small spring was broken, but that wasn't what was causing it to hang up.  The plate that holds the PV into place had broken in half and both bolts had come out.  All pieces were floating around the PV chamber and one bolt had lodged itself under the sub-valve arm which was causing the shaft to hang open and keep the PV from closing.  Unfortunately the plate is back ordered on RMATV, so it may be a couple weeks before I can try it out.

IMG_20170407_151454.thumb.jpg.001f99415087427c6367ad59d4af5c4a.jpgIMG_20170408_081327.thumb.jpg.a78e83d72b1031e5ed196a4f8f988eff.jpg

 

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After a lost package I finally got the PV plate in.  Next problem, went to install and the bolt holes in the head are stripped about 90%.  These are the 2 shorter bolt holes that hold the PV plate.  I could thread about 5mm (guesstimate) of a longer bolt into the hole, so I guess there is some useable threading left.  Problem is I would need some thick washers, etc to make longer bolts work.

Solution? Do I need to get them retapped for a larger bolt?  Back to Langcourt?  Machine shop?  Seems like rigging with the longer bolts and washers would wear out sooner or later anyway.

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I have a partially stripped thread on a power valve cover bolt. I used the copper wire from inside the electrical cable to sort my problem and it's worked perfectly. Just take enough wire to act as the "gap filler", and have it long enough to run the length of the bolt shank. Once you've placed enough copper wire in the hole, turn the bolt into the thread as usual and the copper is soft enough to fill gaps but follow the threading. Mine worked so well I was able to torque to spec.

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That's not a bad idea.  Only reservation is it's an internal bolt and not a cover.  If the bolts do come back out and the copper wire follows, not sure I like the chances or consequences of the wire getting sucked through the PV port and into the combustion chamber.  If it was a cover bolt I'd probably just do that when I got home and call it.

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Bike is back together and running after I slaved away yesterday hand cutting and threading bolts.

Word of advice for threading critical components....make sure bolts are available in the thread count you plan to use.  In my case, they were non existent.  Online, hardware stores, big box stores, all the above...no one has M6x0.8 bolts, and that's what I used to thread my cylinder.  Why the hell is this tap even in the kit??????  Well....one hardware store had M6x0.8 NUTS...but no bolts.  SO...I ended up buying button head allen bolts in M6x1 and using my die to cut the correct threads into those.  An arduous process.  The Harbor Freight tap and dies set I purchased actually worked pretty well for the $15 I paid for it.  I took my time and used ample motor oil in the process, but they worked.

So...cylinder head tapped to M6x0.8, new bolts rethreaded to M6x0.8, and PV plate dremeled out to a slightly larger diameter to accommodate the M6 bolts vs the M5.  Cylinder head and PV disassembled to clean all the shavings out, reassembled and what do you know....while torquing to the specified 52 in.lbs guess what happens?????  CRACK**  The brand new PV plate cracks in the middle before I even hit the torque spec.  I was so tired at that point I just laughed.  It doesn't look to be split the entire way through; but with new threading in the cylinder and the proper bolts (that I loctited) I think the plate will be fine to do its job of just holding the valve into the hole.  Even if it cracks the entire way I think the bolts are in tight enough to hold it.

Word of warning....Careful if you torque this plate to 52in.lbs.  My advice would be to loctite and back down to around 30in.lbs.

Bike runs fine on the stand.  Doing some riding Thursday so hopefully it still runs.

Zebra bolts cut from one thread to another using HF dies.

IMG_20170529_114445.thumb.jpg.3f1e88d38185c5602296a28fafef04dc.jpg

 

Fresh threads

IMG_20170529_114707.thumb.jpg.f2aeb45532f37a41beaafa5195081b58.jpg

 

Brand new broken plate.

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Edited by bcssrmz250

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Nice work with the threading! I can't believe the new plate snapped though! It being new, you can get another under some kind of guarantee through the merchant, right?

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