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Piston failure guide

Discussion in 'Chainsaw' started by PB, Oct 25, 2007.

  1. PB

    PB Addicted to ArboristSite

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    You can't escape yourself
    Does anyone have the Jonsered piston failure guide for download or sale? Might be a good bedtime read.
     
  2. Fish

    Fish Account Hold

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    I have a Stihl book on piston failures, but oddly the pistons in the book are
    all jonsereds and Husqvarna's....................

    Seriously, I was tempted to e-bay it
     
  3. Grande Dog

    Grande Dog ArboristSite.com Sponsor

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    I found this.
     
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  4. PB

    PB Addicted to ArboristSite

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    Thanks, I will definitely use this. I am just curious how the top of a piston can be burnt up. My uncle gave me a 2145 to fix and the piston sides were fine but the top of the piston was burnt to all h___. I was told that using 32:1 ratio burns to hot, maybe this is what caused it. He used cheap oil too.
     
  5. Grande Dog

    Grande Dog ArboristSite.com Sponsor

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    If the piston is deteriorated around the top edge on the exhaust side. It's probably pre-ignition. It's usually found in large displacement saws running low octane fuel. Got any pictures?
     
  6. Poley4

    Poley4 AboristSite Guru

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    :hmm3grin2orange: :hmm3grin2orange: :hmm3grin2orange:
     
  7. stevethekiwi

    stevethekiwi Addicted to ArboristSite

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    new lightweight piston eh

    Timing very slightly out
    Wrong octane fuel
    carbon build up around plug / cyl causing pre ignition
    wrong heat range on spark plug
    turbo charger running a too higher boost
     
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  8. motosierra

    motosierra AboristSite Guru

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    Sick puppy

    You are one sick puppy:)
     
  9. Peacock

    Peacock Addicted to ArboristSite

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    I'm sure it's that one.:givebeer:
     
  10. stevethekiwi

    stevethekiwi Addicted to ArboristSite

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    lol was hoping somine would pick that up :monkey:
     
  11. PB

    PB Addicted to ArboristSite

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    Thanks for the posts everyone, it is a 2145 turbo so maybe LOL. The piston is burnt up on the entire surface of the piston, not just on the exhaust side. I don't have access to take a picture for a couple of weeks sorry.

    This is what I know, the spark arrestor was pretty gummed up, he ran cheap 32:1 oil and probably 87 octane gas. Grande Dog, it is only 45cc so not a large displacement saw at all. I was thinking that it was running too hot, with more oil and a plugged up spark arrestor, would this burn up an entire piston surface? there is no smooth spot on the piston surface at all, very rough. The cylinder is fine and so were the sides of the piston.
     
  12. Grande Dog

    Grande Dog ArboristSite.com Sponsor

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    Stevethekiwi had 4 really good trouble shooting scenario's and 1 for a brain check. A blocked or partially blocked muffler would lead to a rich or cooler running condition. From what you're describing, I would think the hot piston is a recent occurrence or you wouldn't have carbon in the muffler. I would lean towards a timing issue. Could have a partially sheared flywheel key or the timing chip in the ignition is going bad. There might be somebody out there with direct experience with this issue that can shed some light.
     
  13. Erick

    Erick Addicted to ArboristSite

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    When you say burnt up, do you mean that the aluminum is damaged (melted, hole in piston) or do you mean that their is a thick coat of a hard rough black substance (carbon) on the piston top.

    I think an overnight soak in some sea foam and a little elbow grease might show that the piston it's self is just fine, if this is the case you answered your own question as to what caused it.

     
  14. PB

    PB Addicted to ArboristSite

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    No, the metal looked like it sat in acid overnight. Very damaged, no carbon buildup. Sorry for the lack of pictures, I will try to get some soon.

    Thanks Grande, the flywheel key is easy enough to check. Is the timing chip able to be replaced, not too familiar with the timing issue.
     
  15. Erick

    Erick Addicted to ArboristSite

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    In that case sounds like detonation due to pre-ignition. Steve covered some of the possible causes pretty well.

    Your gonna have to crank that Turbo charger down some. :laugh:
     
  16. PB

    PB Addicted to ArboristSite

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    I just like the way the Turbo screams though. :laugh:

    Where do I go from here, replace the ignition module?
     
  17. Erick

    Erick Addicted to ArboristSite

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    Check the flywheel key as was said before, this a pretty rare failure but not impossible and it wont take 5 min. to check. I'm sure you got the saw in the condition it's currently in so you wont know if the ignition is functioning properly until you get the saw back together. At this point I would say buy a new piston and put the saw back together. Make sure you have the proper plug in it and that the flywheel gap is correct. And see what you have then. Pre ignition can be caused by several different causes but if all of the timing issues check out I would say it is probably due to carbon build up and cheap gas. When carbon builds in a cylinder it can get hot and start to glow. When this happens the spark plug and ignition system are no longer in charge of when the fuel/air mix is ignited. The problem is only made worse by the lower flash point of the low octane fuel (always run good fuel folks) and the charge is free to detonate before the ignition fires the plug and timing issues occur.

    In short if you can’t find anything wrong with the saw clean up the cylinder buy a new piston & rings put it back together with the proper plug and good high octane fuel and see how she runs. Good luck
     
    Last edited: Oct 26, 2007
  18. PB

    PB Addicted to ArboristSite

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    Thanks for the info, it is already back together and running. It is set a little low on the rpms for break in. Before I gave it back to my uncle, I wanted to tell him what to do differently. It has a new BPMR7A plug, I think, either way it is the correct plug for the saw. It does seem to be running fine.
     

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