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DR350 Thread

Discussion in 'Thumpers' started by leonphelps, May 16, 2007.

  1. Greg Bender

    Greg Bender Long timer

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    Over the past several months, I've noticed progressively increasing fuel consumption, progressively increasing oil consumption, and progressively decreasing overall power. I decided it was time to give my DR350 some love and investigate. Check out the photo, I'm pretty sure I've found the problem. Top ring speaks for itself. Middle ring is stuck. Oil ring still rotates well.

    IMG_7541.JPG
    Hamburgerhotdog likes this.
  2. slartidbartfast

    slartidbartfast Life is for good friends and great adventures Supporter

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    Uh-oh!

    Is that a stock piston?
  3. Greg Bender

    Greg Bender Long timer

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    Yes, 100% stock. Original piston from the factory with ~39,000 miles on the engine.
  4. everready

    everready Stuck in Ohio....Ugh!!!

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    Why does the piston crown have the step in it? Is that normal?
  5. MrPulldown

    MrPulldown Long timer

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    Wonder how many times that piston went up and down in the 39K miles.
    No not normal.
    The chamfered top edge looks to be normal-ish due to wear. The wear in the top ring grove is crazy though. Looks like the end of the ring wore the extra width; just a little bit with every stroke. Pretty cool actually.
    everready likes this.
  6. plugeye

    plugeye MC rescue

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    hey greg,
    have any numbers to compare? fuel & oil consumption vs. time
    looks like you had maybe another 30K before all hell broke loose
    MrPulldown likes this.
  7. everready

    everready Stuck in Ohio....Ugh!!!

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    What does the cylinder look like?
  8. Greg Bender

    Greg Bender Long timer

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    Here's the cylinder. I'll have my machinist take a look at everything.

    IMG_7542.JPG IMG_7543.JPG IMG_7544.JPG
  9. Greg Bender

    Greg Bender Long timer

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    I don't have any super scientific numbers, especially with oil consumption. I just know that it was going up.

    Fuel economy is also a bit difficult, because different routes I ride have more/less high speed pavement to access them. But, here are three MPG I observed riding very similar routes on subsequent weekends:
    • 50.25
    • 47.76
    • 46.55
    Also, when I was in St. George riding with friends a couple of weekends ago, I noted that I got substantially worse gas mileage than he did. He and I have been on enough trips together that I know we are always fairly close.

    The big clue for me was when I removed the intake boot and a LOT of oil ran out of it. I knew I needed to look further.

    Regards,

    Gregory Bender
  10. MrPulldown

    MrPulldown Long timer

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    Wonder how many DR350 pistons look like that and jsut keep on chugging along
  11. slartidbartfast

    slartidbartfast Life is for good friends and great adventures Supporter

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    Greg Bender likes this.
  12. Greg Bender

    Greg Bender Long timer

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    Yep, I knew something wasn't quite right, but it still ran a lot better than I would have expected.
  13. turboguzzi

    turboguzzi Casual rooster

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    Greg
    Had very similar failure, actually lost a bit of piston crown, had me quite miffed, never happened to me even in my vintage road race engines that often see WOT and 12K rpm... my only explanation is the stock lean jetting of 127.5 on the CV carb. I switched at some point to 140, bike runs lots better, but i guess that the slowly overheating damage by the PO started the crack. 1997 bike with 20K miles BTW

    Attached Files:

    Greg Bender likes this.
  14. memopad

    memopad Been here awhile

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    I know exactly where most of those pictures were taken. Fun place to ride
  15. slartidbartfast

    slartidbartfast Life is for good friends and great adventures Supporter

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    That looks like the failure was next to the intake valves. I'd expect a heat-related failure to have been on the exhaust side.
  16. Greg Bender

    Greg Bender Long timer

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    I'm not sure what the cause was...might be just the piston just wearing out. I'll wait and see what my machinist says.
  17. turboguzzi

    turboguzzi Casual rooster

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    yes and no.... see the pic, the valve reliefs for the intakes are very close to the top ring groove, hardly 2-2.5 mm of meat at the nearest point, easily the weakest point in the crown, the exhaust valve reliefs are further away from the edge ring groove. if bike was working at edge of detonation for a while and piston heat stressed, material would crack where its thinnest IMHO.
    the whole underside of the piston shows general overheating, dont see particular hot spots under the exh reliefs honestly.
    if you have other explanation for the failure, im all ears :)
    no signs whatsoever of valve to piston contact BTW.
    Greg, what jetting and what carb are you running?
  18. slartidbartfast

    slartidbartfast Life is for good friends and great adventures Supporter

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    Fair enough - thinner metal failing first makes sense. Detonation not so likely in a stock DR engine I would have thought. I had some minor pinging in my DR after I trucked it from High-altitude Colorado back to Louisiana. The tank probably had 85 Octane in it.
  19. Friedom

    Friedom Onward and upward!

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    I had similar failure in the same area on the latest DR that I fixed up. The engine still ran, but the piece of ring that snapped off and embedded itself into the head made enough noise to get the PO to stop running it.

    Greg: are you considering a big bore?
  20. Friedom

    Friedom Onward and upward!

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    Heads up, if anyone is considering a Lectron..