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046 big end failure

jb-chainsaws

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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
 

jb-chainsaws

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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.


View attachment 121129

Cheers

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
 

jb-chainsaws

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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.

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
 

Adirondackstihl

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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
 

jb-chainsaws

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If ya got the crank out, might as well do bearings. Just sayin

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
 

MustangMike

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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.

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.
 

huskyboy

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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.
 

MustangMike

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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.
 

jb-chainsaws

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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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