Oil burner/pitted piston
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Thread: Oil burner/pitted piston

  1. #1
    Junior Member liverup's Avatar
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    It was consuming a lot of oil and was pushing oil out the clutch shaft. Why does my piston look so pitted?
    Last edited by liverup; 03-14-2019 at 12:51 PM. Reason: Spelling errors

  2. #2
    Senior Member assquatch20's Avatar
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    It looks like carbon buildup mostly, not actual pitting, but it's hard to tell on a little screen. If you mean your engine was leaking on the clutch side, that could've been the entirety of the issue. Was the exhaust smoking a lot? Did it get better when it warmed up? Since you've already got it apart a new wrist pin, circlips, rings, and a hone would be nice. But you should have the bore checked as it could've been burning oil that was slipping into the combustion chamber. Could also be valve stem seals, but in either case there should be smoking, otherwise it's probably just an oil leak. I hope you had more to go on than just an oil leak before you disassembled.

  3. #3
    Junior Member liverup's Avatar
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    It was burning oil. Lots of blue smoke. I assumed blow by was causing the leak. It would bubble oil out of the clutch shaft on the left side of the engine.
    The top of the piston is real pitted especially near the one valve relief. The piston also looks pitted above the rings. I’m wondering if it was too lean?



    Quote Originally Posted by assquatch20 View Post
    It looks like carbon buildup mostly, not actual pitting, but it's hard to tell on a little screen. If you mean your engine was leaking on the clutch side, that could've been the entirety of the issue. Was the exhaust smoking a lot? Did it get better when it warmed up? Since you've already got it apart a new wrist pin, circlips, rings, and a hone would be nice. But you should have the bore checked as it could've been burning oil that was slipping into the combustion chamber. Could also be valve stem seals, but in either case there should be smoking, otherwise it's probably just an oil leak. I hope you had more to go on than just an oil leak before you disassembled.

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  5. #4
    GOF
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    Wonder what it would cost to punch it over size. As long as you have it apart.
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  6. #5
    Junior Member liverup's Avatar
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    I am planning to bore it. Would like to have valves serviced too. Looking for a machine shop to do it. I’m in rural SD. Not many machine shops around.

    Quote Originally Posted by GOF View Post
    Wonder what it would cost to punch it over size. As long as you have it apart.
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  7. #6
    GOF
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    You can always send it out. Do an internet search.
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  8. #7
    Senior Member Fred's Avatar
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    Looks like heavy carbon build up rather than pitting on the piston, possibly from a leaking valve guide. Cylinder head should also be inspected by the shop when you locate one. By "clutch shaft on left side of engine" I assume you are talking about the output shaft that holds the small sprocket, left side of bike as you sit upon it? That seal should be replaced too. You can do it yourself in your garage if the shop is too far to comfortably transport the engine or whole bike. Ordering seals, plus any other parts, over the internet can save time and money.
    2003 TW200 "Betty Boop"
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  9. #8
    Junior Member liverup's Avatar
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    No it’s not the countershaft seal leaking it’s the clutch shaft linkage. The lever that the clutch cable attaches to. It kind of bubbles out like there could be crankcase pressure.

    Quote Originally Posted by Fred View Post
    Looks like heavy carbon build up rather than pitting on the piston, possibly from a leaking valve guide. Cylinder head should also be inspected by the shop when you locate one. By "clutch shaft on left side of engine" I assume you are talking about the output shaft that holds the small sprocket, left side of bike as you sit upon it? That seal should be replaced too. You can do it yourself in your garage if the shop is too far to comfortably transport the engine or whole bike. Ordering seals, plus any other parts, over the internet can save time and money.

  10. #9
    Senior Member elime's Avatar
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    Here is what a new Yamaha piston for a TW looks like:

    P7210019a.jpgP9300023 (2).JPGPC040032.JPG

    That clutch shaft has a seal on the top. I think you have to remove the left side cover, remove a bolt that holds the shaft in place, slide the shaft up and replace the seal. I have never done it before so read up on it first. Also, as long as the left side is off replace the shift shaft seal, the output shaft seal, and the support bearing seal that is in the left side cover. Also make sure the breather tube isn't clogged -- actually do that first. Maybe that is the cause of your troubles.

    You can get by with a new set of rings and a dingle berry hone job otherwise the magic word is "Wiseco Piston". 67.5, 68.0 and 70.0 mm. The 70 leaves the cylinder wall looking pretty thin but I have not had any trouble with mine. Search ebay "Wiseco 4292" for the smaller piston and "Wiseco 4312M07000" for the big piston.

    If you want to keep the stock bore and try a really big hump on the piston, I don't know if it will clear the head or valves, I have a Venola piston which I think uses stock sized rings and wrist pin.
    P7210018a.jpg
    Last edited by elime; 03-14-2019 at 09:51 PM.
    Fred likes this.
    Long live the internal combustion engine!

  11. #10
    Senior Member elime's Avatar
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    The Yamaha and the Wiseco and the Venola side by side comparison.
    P7210016.JPG
    Sthrnromr likes this.
    Long live the internal combustion engine!

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