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Powervalve Air Leak

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So I just rebuilt my buddies 2008 300 xcw with new piston and all new gaskets and o-rings.  I decided to do a pressure test and it immediately lost pressure.  I pulled out the soapy water and all of the gaskets etc were solid.  I then sprayed in the pv area(I didn't have the covers on) and big bubbles started forming.  I'm curious if this is common on a fresh rebuild?  The KTM pv o-rings don't seem well designed to keep pressure behind them.  I did lightly coat them with grease when I assembled everything.  

In searching this forum I noticed a bunch of posts about oil seeping out the pv covers, which to me means if oil migrates past those o-rings, then air can obviously too.  Is this something to be concerned about or will the 2 stroke oil swell the o-rings for a better seal once the bike has been fired up?  

Sorry for the question but I'm used to a double lip seal on the honda pv's that is designed to hold pressure way better.

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I haven't had any luck getting them to seal either. New o rings,bushings and all. My 05 and my 11 both leak at the shaft when pressure tested.

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1 hour ago, horsinaround said:

I haven't had any luck getting them to seal either. New o rings,bushings and all. My 05 and my 11 both leak at the shaft when pressure tested.

Thanks.  I figure I will start it and if the idle doesn't rev I won't worry about it.  Funny part is with my cr250, if that bikes loses 1 psi in 30 minutes I freak out.  But like I said, all of those seals are double lipped and designed to hold pressure.  A simple o-ring on a shaft can't really hold pressure well and still allow the shaft to rotate smoothly I guess.

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whats your setup to do a pressure test?

 

im about to do a top end here this weekend.

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16 hours ago, cdf450 said:

whats your setup to do a pressure test?

 

im about to do a top end here this weekend.

I actually got a motion pro tester off ebay for real cheap a few years back.  The homemade ones on the honda 2 stroke forum are really simple to make also.

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ok wow. holy crap.  not easy in a small town.   I could have done it differently/cheaper with 1/4 fittings right out of my 90, but nowhere had any!

 

2 hours, 5 stops, and $60 later.... I think I got it figured out.    really should have just ordered the stuff, or a fully built one online!  are all the reed boots generally the same size?  what size should I have gotten....

 

how about the exhaust end?  what size is that? still havnt gotten that cap yet.

 

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Edited by cdf450

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What size 90 did you use? I'm having a hell of a time getting it to bite a 1" with electrical tape around it tight enough. Maybe it's the stock clamp is too weak. And I need an actual hose clamp on there?

For the exhaust flange, the outside is tapered and rippled so a cap would be tough. I got a plug that goes from the inside. Even it's struggling at 8psi

What cases should be off when doing this? Should my whole clutch be taken off?

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I just remove the clutch side oil cap and listen for air. If you hear air you can check the crank seal. I usually will pull the stator cover and take a listen there also.

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so its just a quick check?

 

I can get it to 8 PSI, and itll take 10 seconds to leak out. would that be enough to make the oil cap air sound?  should I be able to hold pressure for 15 minutes?

 

so far im $70 deep and its a total waste of money.  ive got a brand new top end in it now, and going riding!!  

 

I would sure like to get this figured out.. im having a hard time sealing on both ends.  what exactly are you guys using?  part numbers?

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On ‎7‎/‎20‎/‎2017 at 10:23 AM, c-slak said:

So I just rebuilt my buddies 2008 300 xcw with new piston and all new gaskets and o-rings.  I decided to do a pressure test and it immediately lost pressure.  I pulled out the soapy water and all of the gaskets etc were solid.  I then sprayed in the pv area(I didn't have the covers on) and big bubbles started forming.  I'm curious if this is common on a fresh rebuild?  The KTM pv o-rings don't seem well designed to keep pressure behind them.  I did lightly coat them with grease when I assembled everything.  

In searching this forum I noticed a bunch of posts about oil seeping out the pv covers, which to me means if oil migrates past those o-rings, then air can obviously too.  Is this something to be concerned about or will the 2 stroke oil swell the o-rings for a better seal once the bike has been fired up?  

Sorry for the question but I'm used to a double lip seal on the honda pv's that is designed to hold pressure way better.

What you experienced is perfectly normal.  You are right.  The seals don't seal air in that way for a pressure leak down test.  They don't need to.  Put in some premix, run 'er and be happy.

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Old topic, I know, but same here. I have a '15 TE300 that I can pump up to 6psi, and have it hold indefinitely, but then I'll jiggle the powervalve a bit and I lose pressure at a rate of 1psi every 20-30 seconds. But then I can jiggle it again and it'll maintain pressure just fine.

Not sure what to make of that...

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