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046 big end failure

Discussion in 'Chainsaws' started by jb-chainsaws, Apr 17, 2018 at 10:20 AM.

  1. jb-chainsaws

    jb-chainsaws Pinnacle OPE Member

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    just started tearing into an 046 that came in with “low compression”.

    Piston looked scored from exhaust side so I was thinking maybe air leak, til I got the jug off:

    1A8B2683-63E0-48F7-BD3F-529EF0C11513.jpeg 02BA3797-0518-4F5E-AB97-ABA72185E80A.jpeg

    The transfer might have cleaned up, but the bore is “peppered” with tiny pits. The culprit is below:


    9559A945-9AE2-4F93-8EB0-C9E505054305.jpeg

    Big end bearing failure, if you zoom in on the photo you can see the retainer is starting to break up.

    I figured I’d post this as it’s not something you see every day.

    Thankfully I’ve a 460 in the boneyard with a good crank, otherwise it’d have been an even more costly repair. Fingers crossed the crank bearings survived
     
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  2. Wonkydonkey

    Wonkydonkey Super OPE Member

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    Umm, well I see bluing at the big end, I think I can see the bit you mean.

    But also I noticed the colour of the plug, a bit too white for my liking.


    BB9B127C-D74F-4F78-AAA8-C8687F73B373.jpeg

    Cheers
     
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  3. jb-chainsaws

    jb-chainsaws Pinnacle OPE Member

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    That’s the bit, when I look closely with a good light you can see hairline cracks in the corner of each bearing “pocket” if that makes sense. It’s a shame as the cases are really clean for its age! What’s a decent 046 go for these days? Less than a 460 in work clothes? If so I might build up the 460 with the 046 parts, as that’s got a good bottom end and a cylinder than cleaned up nicely but no covers, brake etc
     
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  4. Chainsaw Jim

    Chainsaw Jim Will Willis Man Bun Fan Club

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    Clean the cylinder up and run it. Small pits like that usually don't grow, but check after a tank or two to make sure.
     
  5. jb-chainsaws

    jb-chainsaws Pinnacle OPE Member

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    I’ll give it a clean and see how it comes out, cheers for the info. I’ve always been cautious about running jugs like that
     
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  6. Adirondackstihl

    Adirondackstihl Vert Da Furk........Bork Bork Bork

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    I’ve seen tiny pits in about every 1128 cylinder I’ve had on my bench.
    From low hour saws to saws that were way past their service life.
    I’d clean that cylinder and run it without thinking twice.
    The crank on the other hand........meh I don’t know bout that
     
  7. Deets066

    Deets066 AKA Deetsey

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    If ya got the crank out, might as well do bearings. Just sayin
     
  8. jb-chainsaws

    jb-chainsaws Pinnacle OPE Member

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    Yeah on second thought I’m gonna sit this case on the bench for now, I’ll rebuild the 460 with the 046 parts. Gave £100 for the 046 and it needs a bit much spending on it to be worth doing so it can be a boneyard Saw at least for now
     
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  9. blsnelling

    blsnelling Friend of the Riff Raff

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    Those pits aren't from crank failure. The cage looks intact to me. The blue might or might not be a problem. Many Stihl cranks are blue from heat treating.
     
  10. MustangMike

    MustangMike ONE OF THE GREATEST!

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    IMO you got it the opposite. Many people will pay a premium for a 046 screw cap saw over a 460 flippy cap.

    I don't happen to be one of them, but there is strong sentiment out there.
     
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  11. RI Chevy

    RI Chevy Stihl Runner

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    Probably set to lean! At 50:1.
     
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  12. MustangMike

    MustangMike ONE OF THE GREATEST!

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    I agree, with scoring only on the exhaust side, looks like a lean heat fail to me.

    Re: crank bearing ... I'm not going to make any judgement from pics, but does it rotate smoothly, etc? Make sure you don't let your imagination create addl problems. Check if it has any lateral play.
     
  13. huskyboy

    huskyboy ONE OF THE GREATEST!

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    I have a 440 carcass with crank that’s blue on both ends... yet the crank is fine. I think it’s from how they harden the rods from heat treating at factory. I don’t think color alone means a crank is junk. If the cage is suspect then toss it. I’d replace bearings if it’s torn down that far.
     
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  14. MustangMike

    MustangMike ONE OF THE GREATEST!

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    He is worried about the big rod bearing, the one you can't replace!
     
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  15. firefighterwolf

    firefighterwolf Well-Known OPE Member

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    He also mentioned the main bearings: "Fingers crossed the crank bearings survived"
     
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  16. MustangMike

    MustangMike ONE OF THE GREATEST!

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    The first thing I would do is pressure test the saw (after checking the big rod bearing). A good seal usually means a good bearing, and vice versa. Of course, also check that it rotates smoothly, but I would flush the case with mix first, that lean seize can't be good for anything.
     
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  17. jb-chainsaws

    jb-chainsaws Pinnacle OPE Member

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    Big end bearing is most definitely toast, and that blue on one end of the rod doesn’t look like heat treat. There’s a tiny amount of lateral play in the bearing, between that and the hairline cracks in the cage I’m probably gonna give this a miss. The amount extra I’d spend building this one vs the 440 I don’t tbink would be reflected in the sale value, as it’s a Saw i’d be flipping anyway. Thanks for all the suggestions chaps
     
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