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MS 661C M-Tronic Repair

Discussion in 'Chainsaw' started by Wood Doctor, Oct 9, 2018 at 2:06 PM.

  1. Wood Doctor

    Wood Doctor Edwin

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    You guys may find this post interesting on a rainy day. A logger backed over his MS 661C M-Tronic with a 25,000 lb skid loader. The handle bar looked like a pretzel, somehow the bar and chain survived, and the engine still had compression and turned over. He decided to have me repair it. That required over $500 in new parts -- handle bar, brake handle, tank housing, air filter, filter base, AV spring, pull cord housing, etc. It adds up fast. He claimed that after he ran over it, the saw started and ran, so in his mind, repairs were thus justified.

    I was skeptical, but compression was at 155 psi., so I went ahead and ordered the parts. Well, lo and behold, I also discovered during the repair that the fuel line to the carb was completely broken off along with the carb's intake nipple. And, the intake manifold boot was cracked almost in half. So, the carb was not getting any fuel from the tank, and even if it did, any fuel-air mixture should have been lean.

    As such, how long could this engine have run after it was squashed, assuming that he actually did start and run it? Any ideas?
     
  2. Wood Doctor

    Wood Doctor Edwin

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    No Pic, didn't happen, right? Take a look at this:
    Stihl MS661C Tank Housing.JPG
    I rest my case. (1) How did this saw start and run? (2) If it somehow ran with these three parts on board, how long did it run? Any ideas? WDYT?
     
  3. Wood Doctor

    Wood Doctor Edwin

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    So, nobody wants to venture a guess? Well, I went ahead and repaired the saw with the parts listed in post #1. It started and runs today. How did the logger know that I could repair it? I've never seen a saw engine run with a disconnected fuel line as shown in post #2. What was it running on? Maybe fumes from the skid loader that ran over it? You learn something every day.
     
  4. ericm979

    ericm979 ArboristSite Operative

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    He probably started it on the fuel remaining in the carb then shut it down.
     
  5. Wood Doctor

    Wood Doctor Edwin

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    That's what I figured, but I have no idea how long that run time would last. Maybe 5 seconds at most? Had the engine been cold, I doubt it would have fired. I really don't see how he could have concluded that the engine was still good.

    BTW, I found more broken pieces on the case as I went along. This saw should have been trashed, but he insisted that I piece it together. I doubt he could ever sell it for the cost of the OEM parts.
     
  6. Gord404

    Gord404 ArboristSite Member

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    Just had 2 390's come through here, one fell off a cliff and the other a log rolled over it or something like that, one was only 10 days old, bought them and a couple of other saws and all up and running again, living in an active logging area you get a lot of altered saws and parts.
     

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