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Cause of Failure??

Discussion in 'Chainsaw' started by Ck0461, Jul 13, 2018.

  1. Ck0461

    Ck0461 ArboristSite Operative

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    Burned up a Husqvarna 359 the other day. This saw was in need of a few things and was a great saw for a long time. I put a new modded muffler, oil lines, crank seals and piston. It passed a vac test and I tuned it to 12500 rpm for the break in. Ran as it should for the first tank, and all the second till it died in a cut. I’m guessing it leaned it self out on a nearly empty tank or developed a leak. It was four stroking and never ran any different. Most pistons I've seen have a lot more damage on them from lean conditions and there wasn’t much of any transfer on the cylinder wall. The other cause that I could think of is just an overheating of the cylinder because of the muffler. I basically cut the top piece off the falling apart OEM muffler and welded it to the AM in the same location, leaving the AM opening alone.
    I’ve already got the saw running again, but wanted to get a few opinions before taking it back out. Thanks for everyone’s knowledge and opinions. 44812CFE-1339-4B5A-966A-F94431A0AAE2.jpeg
     
  2. Brushwacker

    Brushwacker Addicted to ArboristSite

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    I don't claim to be an expert, but I''ve saw lotta 2 stroke pistons damaged by this and that. I agree looks heat related. Does any of your exhaust get backed up between the muffler and cylinder ? I was running an 385 xp once that the loose muffler allowed that to happen and that coupled with leaner running which I didn't notice allowed it to seize. Hotter weather would factor in also.
     
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  3. Chainsaw Jim

    Chainsaw Jim Addicted to ArboristSite

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    I've seen that exact same looking damage from running bad fuel.
     
  4. Mattyo

    Mattyo Youtube Speciawist

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    Plastic intake clamp or metal?
     
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  5. Bobby Kirbos

    Bobby Kirbos Scrounger of Cellulose Based BTUs

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    Please define "bad fuel". Old gas? Not enough oil? Water in the gas?

    I'm wondering if this is the same sort of thing that led to the failure of the Dayton saw that I am working on.
     
  6. Ck0461

    Ck0461 ArboristSite Operative

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    Metal intake clamp. The old muffler was coming apart on the inside, rattling a lot. Fuel came from the same can that I ran other 2 saws. Air temp was pretty hot that day.
     
  7. Brent Nowell

    Brent Nowell ArboristSite Operative

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    Fascinating

    How easy was the saw to tune? If you found yourself adjusting all the time especially for idle its a good sign of an air leak.
    Im also wondering if the old muffler baffle or inner deflector whatever you want to call it helped block exhaust gas flow. This could give you your overheating condition.

    Pull the muffler, inspect it, get a screw driver in there and a flashlight and see if you can replicate a blockage.
     
  8. Ozhoo

    Ozhoo Addicted to ArboristSite

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    Next time, do a vacuum test before you disassemble. Till then it's guessing.
     
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  9. Mattyo

    Mattyo Youtube Speciawist

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    Yup....guessing.

    Bad bearing causing a seal to leak?

    Hole in fuel line? / cracked line....look right at the junction at the tank
     
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  10. Chainsaw Jim

    Chainsaw Jim Addicted to ArboristSite

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    Old fuel when it starts breaking down and starts getting gummy. A contaminated can.
    Bar oil seeping through the case gasket will also do it.
     
  11. alderman

    alderman Addicted to ArboristSite

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    I'm very much a mechanical idiot but could it be a lean situation if it were four stroking? Serious question as I really would like to know.


    Sent from my iPhone using Tapatalk
     
  12. sunfish

    sunfish Fish Head

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    Four stroking is a rich condition. Too lean and no four stroking at all.
     
  13. sunfish

    sunfish Fish Head

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    Assuming no air leak and good fuel mix, something wasn't right with the P&C.

    Was all the transfer clean out of the cylinder? The first time?

    What was the replacement piston? Cheap Chinese or?
     
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  14. Ck0461

    Ck0461 ArboristSite Operative

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    Thanks for all the questions and ideas. I double checked the fuel lines again. The piston was a hyway brand. I’ve had good luck with hyway stuff so far.
    The saw tuned easy. I started rich, and kept raising the rpms 300-500 till I got to 12500. Witch is still on the rich side for the saw.
    That’s what’s got me second guessing myself. There were no warning signs for the failure. (Bad idle, chasing the tune, or high rpms)When it happened I thought the coil failed the way it died. Everything inside and out looked ok to me before and after the failure. (Other than the piston)
    I’m going to run it some tomorrow and see if it acts up. I’ll let y’all know what happens.
     
  15. sunfish

    sunfish Fish Head

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    But was there in transfer in the cylinder from the first piston? Or was the original piston not scored?
     
  16. JimM

    JimM ArboristSite Guru

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    Cylinder base gasket area looks funky.
     
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  17. Ck0461

    Ck0461 ArboristSite Operative

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    Yeah there was some transfer from the first piston. Cylinder ceaned up real well. It had 155psi compression before break in.
     
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  18. sunfish

    sunfish Fish Head

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    OK well that rules out that. Maybe just a bad piston? I only use Meteor replacement pistons, not Hyway.
     
  19. Ck0461

    Ck0461 ArboristSite Operative

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    Base gasket split in two.
     
  20. JimM

    JimM ArboristSite Guru

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    Dead center on the front? Goop it up and hope for the best, did you?
     

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