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Cleaning piston, valves and combustion chambers

Discussion in 'The Garage' started by peterg, Nov 23, 2021 at 4:45 PM.

  1. How aggressive can I get with cleaning pistons, valves and combustion chambers? Carbon was 2 - 3 millimetres thick! I used paint stripper, Gunk and the end of a hacksaw blade to remove most of it. What should I use to finish up?
     
  2. Signal

    Signal XS650 Junkie Top Contributor

    A tip I picked up from this site is to soak them in water. I have tried it and it works. I left them soaking a couple of days
     
    Mailman likes this.
  3. willis

    willis xsive compulsive disorder XS650.com Supporter Top Contributor

    The valves are hardened. Chuck up a wire wheel in the drill press. You won’t hurt them.
     
    Mailman likes this.
  4. 5twins

    5twins XS650 Guru Top Contributor

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    Yes, the valves are hardened steel so a strong wire wheel is fine. I use the knotted brush type in a 4 1/2" grinder, very aggressive and cleans them up fast. For the combustion chambers and pistons, after the paint stripper, I use plain old chrome polish on them. Any little remaining spots of carbon I'll carefully scrape off or use the little wire wheels in a Dremel. The paint stripper has usually softened the carbon up so it scrapes off pretty easily.
     
    gggGary likes this.
  5. 0514745C-FDB7-44E8-91C5-6011BE632359.jpeg 4F64B829-97C0-4BD2-AA4E-C181AAE82E0E.jpeg Thanks for the replies. I’ll try the water soaking method on the valves followed by my dremel with a wire brush (I don’t have a drill press). Any concerns about the stems getting marred?

    5twins. I was concerned about wrecking the chambers with a wire brush but I’ll go ahead with it now. Thanks.

    How about the piston tops? I’ve lightly used a scotch bright pad on them but they are still stained.
     
    Last edited: Nov 24, 2021 at 8:07 AM
  6. 5twins

    5twins XS650 Guru Top Contributor

    22,078
    15,900
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    Try chrome polish with an old toothbrush. here's one I cleaned up that way (after paint stripper) .....

    [​IMG]

    [​IMG]

    [​IMG]

    This is about as good as you'll get it.
     
    gggGary likes this.
  7. cra-z1

    cra-z1 XS650 Guru Top Contributor

    I throw my pistons in the ultrasonic cleaner, then what's left a little scrubbing pad. The valves I blast with SS media since they will be resurfaced.
     
  8. I’ll give it a go. Thanks.
    I wish I had access to that equipment!
     
    gggGary likes this.
  9. Jan_P

    Jan_P XS650 Guru Top Contributor

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    Thinking out loud here aren't the piston skirts a bit scratched
    Indicating some miles driven
    +
    Carbon was 2 - 3 millimetres thick!

    Not saying what is right or wrong here other factors can be important
    but if it is a high mileage bike with the intention to keep and make better
    Other options could be considered

    There are inspection routines in service manuals on line
     
  10. 5twins

    5twins XS650 Guru Top Contributor

    22,078
    15,900
    813
    Yes, I was going to mention the piston wear. I measure and check them against the bore to make sure they're still OK to use before going through all the trouble of cleaning them up.
     
    cra-z1 and Jan_P like this.
  11. The bike has about 50,000 K (32,000 miles). I’ll look into measuring and checking some more. First time top end rebuild for me.
     
    gggGary and Jan_P like this.
  12. 5twins

    5twins XS650 Guru Top Contributor

    22,078
    15,900
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    Well, with that many miles, I'm going to guess that the piston wear combined with the bore wear is going to be out of spec and call for an over-size bore and pistons.
     
    Jan_P likes this.
  13. Jan_P

    Jan_P XS650 Guru Top Contributor

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    Yes Sir probably right .. but if the financial aspect is important
    A bore is expensive here $ 300 range
    I feel that compression is not so important for the bikes performance Ignition and carburetor adjustment plays a bigger role
    It Can rattle a little and feel soft on the kick ..Bur run fairly well The measurements will tell.
     
  14. Jan_P

    Jan_P XS650 Guru Top Contributor

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    Quick Easy and Entertaining turn the cylinder head upside down level ... with spark plugs in pour gasoline up to the edge
    Start the stopwatch see if the gas stays there preferably outdoors and be careful with fire
     
  15. cra-z1

    cra-z1 XS650 Guru Top Contributor

    Out of all the engines I have done none of them had bores that would qualify for just a hone. Yes the bike would probably run with just a hone and new rings but the bores were all out of round, that's even with engines with less than 20,000 and some had around 12,000. The material they used back then was just not that good. So I end up with new pistons and rings with bore and hone. I do this because I do not want any surprises after the build. It gets a bit expensive but its nice when you start the bike up for the first time without any problems.
     
    Mailman, Team Junk, GLJ and 1 other person like this.
  16. I’m in for the long haul so I’m going to get a rebore and oversized pistons. No point in doing a top end rebuild unless I do it right.
     
    Jan_P likes this.
  17. Jan_P

    Jan_P XS650 Guru Top Contributor

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    Thinking out loud again
    It is a in my view interesting and rewarding hobby to work with these machines As with other Mechanical equipment.
    But in the rebuilding decisions there is also the economical aspect. It cost money
    Even though the XS 650 is the perhaps best in that sense .It does not have to cost a lot of money
    At least not in the past .Given that there are lot of parts. Available .At times at low prices

    How is the status of the lower end con rod small end and crank ?
    What year model ?
     
  18. Jan. I haven’t taken apart the lower end and I don’t intend to so I can’t check the condition of the parts. It’s a 1980.
     
  19. Team Junk

    Team Junk XS650 Guru XS650.com Supporter Top Contributor

    There are 700 cc pistons on fleabay etc. Not heard anything bad about them.
     
  20. Team Junk

    Team Junk XS650 Guru XS650.com Supporter Top Contributor

    Roughly a 9 per displacement increase. Anyone have an idea of the CR of these pistons. In theory the displacement increase would result in 9.3 CR.
    You could spend a lot of money on pipe,carb , foam filters etc to get about the same gain. There ain't no substitute for cubic inches.
    I think they use the stock liners bored to 87mm. Good chunk of the 750 kit advantage without dealing with sleeves etc.
    https://www.cruzinimage.net/2017/08/29/74-81-yamaha-xs650-706cc-bigbore-pistons-kit-78mm-447type/
     
    Raymond and Jan_P like this.

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