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Thread: Exaust valve pitting

  1. #1
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    Default Exaust valve pitting

    So I decided to get into my '16 350 xcw for the first time, I probably should have left it alone. It has been running great and the leak down test I did just prior to teardown was 2.5%. Couldn't hear any air coming from intake or exhaust, just the crankcase so it would seem the valves were working pretty good. I tore it down expecting to put a new piston in it, is has 270 hours on the motor. I got the head apart and cleaned up the valves, the intake valves look brand new. The exhaust valves are both showing some pitting. What do you think, new titanium valves at $200 ea?


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    Interestingly enough, I inserted both valves into the head and just pushed them down, no springs installed. I made a puddle of alcohol on the valves and surprisingly they didn't leak. Puddle wasn't to deep though but I didn't see any sign of the alcohol when I looked up the exhaust port. So can I take any comfort in the fact that they aren't leaking (much) or do I just bite the bullet?

    BTY, The piston had plenty of carbon. Compression ring gap measured 20mm down was .014" which is still in spec according to the KTM manual.
    Click image for larger version. 

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  3. #2
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    Default Re: Exaust valve pitting

    How did you clean the valves?

  4. #3
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    Default Re: Exaust valve pitting

    Used ultrasonic plus a little scrubbing. The pits were visible prior to cleaning also.

  5. #4
    KTMTalk Member DJH's Avatar
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    Default Re: Exaust valve pitting

    Pits are from grit leaking in at the head pipe connection. After the exhaust rushes out there is a vacume behind it so dirt is sucked in then he valve closes on it. try to get a better seal there
    [URL=http://www.djhcyclesport.com
    Former Husky Dealer in the '70's, currently Sell Real Estate, Seattle area and as a hobby business I manufactor cam chain tensioners for the KTMs, do Carburetor modification & setup and valve work on KTM & Husky 4 strokes. Full stock of parts for the KTM's. My rides are; Cadillac Escalade (the 1/2 pickup version), 72 ElCamino 454SS, and Triumph 1050 Sprint ST, Iron Butt member

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    Default Re: Exaust valve pitting

    Quote Originally Posted by DJH View Post
    Pits are from grit leaking in at the head pipe connection. After the exhaust rushes out there is a vacume behind it so dirt is sucked in then he valve closes on it. try to get a better seal there
    Interesting, I've never heard that. I thought the pitting was caused by carbon passing through the valve. This is the first time the header has been off so I'll checkout what the sealing situation is there. Will high temp rtv work?
    Do you think the valves are toast? If so is the stock valve the best replacement or after market?

    thanks
    Last edited by roberttt; 01-14-2020 at 10:03 AM.

  7. #6
    KTMTalk Member DJH's Avatar
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    Default Re: Exaust valve pitting

    The Del West valve is the only thing that lasts at the RPM these engines run, I would be temped to put them back in
    Hightemp RTV will help
    [URL=http://www.djhcyclesport.com
    Former Husky Dealer in the '70's, currently Sell Real Estate, Seattle area and as a hobby business I manufactor cam chain tensioners for the KTMs, do Carburetor modification & setup and valve work on KTM & Husky 4 strokes. Full stock of parts for the KTM's. My rides are; Cadillac Escalade (the 1/2 pickup version), 72 ElCamino 454SS, and Triumph 1050 Sprint ST, Iron Butt member

  8. #7
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    Default Re: Exaust valve pitting

    Thanks Dave. Is there a way to check my valve guides without the special gauge pins?

  9. #8
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    Default Re: Exaust valve pitting

    While I usually agree with dave judging by the carbon build up on the piston your damage is from carbon off the piston getting caught as the valves close. Unless you have a gross leak at the header the bulk of that damage came from carbon build up falling off the piston. If you plan on rebuilding in the next year then dont worry about the valves if you are more a run it till it blows replace the valves.

    Did you check ring end gap I'll bet its larger than it should be based on the carbon build up.
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  10. #9
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    Default Re: Exaust valve pitting

    Thanks Travis.
    I did check the compression ring gap and it was at .014" Not too bad so I'm not sure why so much carbon. Too much lugging?

    I really don't want to get back into this engine for another 200 hours if I can help it. Cylinder is at the machine shop getting measured so assuming it is fine, my plan was new piston, new valve seals, I guess maybe new exhaust valves. Only thing I an unsure about is the valve guides, I don't think I have the ability to check them. The valve seats look good, can I just drop some new valves in and be OK or should they be touched up?

  11. #10
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    Default Re: Exaust valve pitting

    Is the excess carbon due to oil consumption? With top end?

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