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18 150sx Sticky Power Valve?

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Hi All, I currently have the cylinder off of my 18 150sx.  I've cleaned & lubed the power valve assembly, but  I notice it is still very difficult to move the power valve by hand.  I was wondering if others had the same situation?  Is this normal for these power valves?  I suspect it's related to the rubber O rings that are used in a few places in the assembly, but I wanted to check.

Any tricks to free the PV up so that it moves more freely?  thanks

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Warm it up with a hairdryer ,and see if it works normally ,they often don't stick when at operating temperature

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not to change subjects..., but I also notice there is an additional PV adjuster (allen bolt & lock nut) that allows you to set the amount distance the valve will move when fully closed.  Has anyone played with that adjustment?  I notice that PV could still close a bit more, if I did choose to use this adjuster

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Yes it's in the manual ,I've never tried to adjust it away from standard, if you lower it ,you run the risk of it not fully opening

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It's totally normal on the 150. The side valves in particular are really difficult to turn by hand. I had several discussions via my dealer with KTM in Austria regarding this.  It works perfectly well when the engine is running. You should only really use the adjuster bolt on the front left of the cylinder to set dimension Z. Bob

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The Powervalve does feel sticky when operated by hand.  Even when new, I was surprised how "notchy" it felt.  The culprit is the very aggressive geometry of the powervalve arms.  KTM designed the system to open the sub exhausts (side exhaust ports) very quickly, which results in a lot of force required to move them.  As stated above, once the engine is running, the heat and vibration help the system work properly.  I have 40hrs on my powervalves and haven't cleaned them yet (don't need to be cleaned yet) and they work fine.  The small allen bolt is a "down-stop" adjuster to set the closed position height of the main exhaust flap.  This is set at the factory and should only be adjusted if the main flap height differs from the measurement given in the manual.

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I see an Australian company make arms with a slightly different 'run' which they claim solves this issue. Not particularly issue though. For some reason both our 125s turn smoothly by hand. Strange.

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Thanks for the feedback.  I've cleaned and polished every surface I could find, so I'll test the operation once I have it back together and running.  The alternative arms do sound somewhat interesting, I'll see if I can find them online.

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Hi, It's f1moto.com/au who sells them.  Anyway, we fitted a 150 kit to one of our 125s for open winter racing and I found the valves really tight compared to the 125 (they are bigger hence come with the kit). Got the same answer 3 times from KTM so fitted it. Soon as it was started with the left hand cover off saw the valves were running up and down the guides just fine. Can't help thinking it must sap a bit power? Guess the engine is stronger than my fingers lol. Bob

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On the Dyno you can get a almost perfect straight line ,so I can only conclude it works as its intended

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5 minutes ago, mog said:

On the Dyno you can get a almost perfect straight line ,so I can only conclude it works as its intended

It was only a thought as it looks really tough for the valve pins to run round that curve. However as you say it obviously works as intended. Not sure why both our 125 ones are so easy to click between open and closed. 150s pah! lol Bob.

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Lots have said the 150 ones are sticky ,mine wasn't so I guess I got lucky ,however my head was 0.15mm more squish than most 150s so that's was the part I wasn't lucky on lol

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I got lucky and my PV's are reasonably smooth and my squish was perfect!  Yeehaw!!!  lol

Edited by dshissam
typo
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On every engine rotation there is a new pressure pulse forcing the power valve to open. The pv control arms more likely just restrict the pv from opening when engine is running, even if they are bit sticky.

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I did polish the cams, add mome light grease to the cams and the slots in the control arms, better for sure.  I'll wait to see how they work when it is running again.  FYI, i did check the Z dimension, and that was spot on.  I'll stick with the stock arms for now.

Regarding base gasket, any harm going with a smaller one?  I mic'd my original gasket at about .60mm, and I would like to go a litter thinner, possibly .40mm.  I'm chasing a little more low end if possible, but I dont want to be forced to run race gas

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The stock base gasket arrangement for all of the '18 150sx's has been a stack of TWO gaskets (0.25mm for the first gasket and 0.40mm for the second gasket) resulting in a total height of 0.65mm for the base gasket.  Mog (has commented in this thread) has done extensive cylinder height testing and numerous dyno runs.  I don't want to speak for him, but just lowering the cylinder itself may not be the answer for more torque (although this works on most other bikes...) and hurts the over all power spread.  

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2 hours ago, dshissam said:

The stock base gasket arrangement for all of the '18 150sx's has been a stack of TWO gaskets (0.25mm for the first gasket and 0.40mm for the second gasket) resulting in a total height of 0.65mm for the base gasket.  Mog (has commented in this thread) has done extensive cylinder height testing and numerous dyno runs.  I don't want to speak for him, but just lowering the cylinder itself may not be the answer for more torque (although this works on most other bikes...) and hurts the over all power spread.  

interesting, I have a single gasket that is .60.  I'll see what happens with a .40 base gasket as it's not that hard to go back to .60 if needed

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Interesting about your base gasket. KTM only offers thicknesses of 0.15, 0.20, 0.25, 0.40, 0.50 and 0.75mm for the base gaskets. Is your base gasket OEM? If so what color is it?  All the OEM base gaskets are a teal green except the 0.15 (yellowish) and the 0.25mm which is like a beige color. My piston was .0025" or 0.064mm below flush of the cylinder deck at TDC (what KTM calls the "Z" dimension).

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I had my best peak power with 0.4mm and it's not going to do any harm unless you run terrible fuel

My latest dynos with raised ports was done after the Dyno developed a problem with the hardware ,it shows a drop in power across the board so it's hard to say if that mod is good or bad

I would try 0.4mm

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