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I think i have a burnt valve...90psi right side

Discussion in 'The Garage' started by Square Circle, Sep 14, 2012.

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  1. Square Circle

    Square Circle XS650 Addict

    Now what? How much is this gonna cost me ? what parts should I look into replacing once the head is off? I have'nt put my nose in the manual about this yet. This is Not what i was wanting to have to do .. and its looking like my fall :bike:riding will be a no:( go. Oh well, the project is so much more fun....:laugh:...
    I tried this..http://www.xs650.com/forum/showthread.php?t=11693.. but did'nt work.. the valve still looked like crap just a little less charcoaled when i was done scrubbing it.. . i'll take a pic of it later for someones evaluation.
     
  2. 5twins

    5twins XS650 Guru Top Contributor

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    Well, the valve isn't necessarily burnt up. It could be just badly pitted or carbon coated. Valve seats and faces develop pits over time, that's just normal wear and tear. Eventually, the pitting gets bad enough that they start leaking. If the bike was run too rich for a long time, the combustion chamber can get heavily carboned up. Eventually that will coat the valve seats and can even creep down the sides of the piston and cause a ring to stick. Coating the valve seats is like carpeting a hardwood floor. They may look smooth but that layer of carbon is soft and the valve won't seal to it.

    Figure about $200 to do the top end if you need the minimum stuff done - new gaskets, cam chain, front guide, and rings. You will be hand lapping the valves to seal them up again but the cost of that is minimal (about $10 for the lapping compound and lapping stick). If you need to get it bored and buy new over-sized pistons, the cost will about double.
     
  3. Square Circle

    Square Circle XS650 Addict

    Thanks 5twins. Its obvious this bike WAS run rich for a while.. Lots of carbon build up. I think i can get it to run just well enough to get it state inspected and licensed not far from home.. then.. order the parts .
    Hand lapping the head sounds like "experienced mechanics only" kind of work.. Can a beginner do this?
     
  4. 5twins

    5twins XS650 Guru Top Contributor

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  5. Do a leak down test before taking it apart. It will tell you exactly where it is losing compression and how much. You can pin point it to intake valve, exhaust valve or rings. Only places it can leak.
    You can buy them for about 50 bucks or make your own.
    Hope this helps.
     
  6. Square Circle

    Square Circle XS650 Addict

    Thanks rebel, I did the leak down test.. my comp. guage has air hose couplers on it. i initially set the psi on compresor to 100 but it bluew the wrench right out of my helpers hands.. After se setting engine to tdc with valve closed, i lowered pressure to 35 psi and could hear a moderate air leak from the exhaust pipe on that side,. I don't know an exact measure or percentage of air loss leaving my air compressor, but this would confirm an unseated valve.. I had the pipe off before hand and could see the huge amount of carbon build up in there.. I cleaned what i could with a small brass brush from a gun kit, afterwards things looked a little pitted and rough.. The test just confirmed the problem. If i'm going to repair it, i'm now considering having the cylinders bored over once or twice as needed possibly.. dunno yet.... the bikes got over 18xxx on it and obviously was not maintained the greatest. Engine rebuilding sounds fun..parts, new tools, etc ...etc... but my budget says.."Buy a plastic model bike from hobby shop and stick a noise maker in your bicycle spokes"http://www.youtube.com/watch?v=iWl-aKMRq40 LOL.
     
    Last edited: Sep 16, 2012
  7. Sounds like you're on the right path. Good luck with it.
     
  8. Square Circle

    Square Circle XS650 Addict

    Yahoo!! false alarm. it looks like i was a bafoon (no surprise here) i set my valve gaps on that exhaust valve to .006 .. same as inlet valve.. duh.. and after resetting to the proper 0.15mm and then blasting around the subdivision, it seems like the last bit of carbon bits were cleared away from the seat.. and i now have 140 psi on both cylinders.. RIDE TIME:bike:
     
  9. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

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    great news ! and an informative thread to help others as well.

    Someone last week had low compression one cylinder and I'm convinced he has the exhaust valve gap incorrectly set
     
  10. 5twins

    5twins XS650 Guru Top Contributor

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    Now the fun starts. You're to the point where you can "ride and wrench". Ride a little bit, fix this, ride a little bit more, fix that. It can take a couple seasons to get one of these fully sorted and fixed up.
     
  11. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

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    thats the whole thing about running these bikes isn't it . !

    Any fool can go and buy a new bike on credit and run it without problems.

    It takes a special kind of fool to buy a 30 year old heap and some wrenches and go on a voyage of discovery :thumbsup:
     
  12. ippytattoo

    ippytattoo Just another grumpy hack.

    I guess I am one of those "SPECIAL" fools twice over as this is the second xs I have purchased and gotten back on the road either through blind luck or shear will and determination.
     

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