Is my bottom end shot ?

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TysonH

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A while back I pulled my saw apart to adjust the squish and noticed the heat signature on the bottom bearing my guess is that this of shot can you confirm ?

I've owned it for about a year now (purchase off of eBay yeah I know lesson learned) I run only fresh fuel and run HP ultra at 40:1 I'm guessing this didn't happen on my watch. I have to say it runs perfect and there are no signs of any bearing plating floating around in the case . The piston and cylinder are in great condition someone got this thing hot and I'm not sure how only the one bearing The upper is fine and there's no play in any of them.
 

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No sir, no play directly up or down motion, like I said before everything runs great all bearings feel tight and smooth. And yes I was concerned about the bluing on the bottom of the rod.

How do you suppose that bearing got that hot and nothing else showed signs of wear or heat like that bottom rod bearing ?
 
If it got that hot and even if there is no play it's not going to last long .
Sorry......
 
Well, you would never had suspected an issue if you hadn't pulled the jug. I'd run it, but be mentally prepared to potentially add the cost of a new jug to the PITA factor of splitting the case. Of course, my saws are pretty beat up to begin with.
 
Thank you gentlemen that's the answer I was hoping for and I was about to put an ad up for a bottom end. Sweet!
 
That bluing is the manufacturing process to harden the rod
at the bearing surface. Seen it many times.
As Brad said. Run it.

Really ? , ok ...whatever hahaha .

TysonH , I hope she holds together but if the bearing starts to fail the bits from it will end up in your jug .
And that's not to say it won't last but that bearing has got very hot and it's going to effect the hardening of the bearing and conn rod .
 
If the rod got that hot in-place, wouldn't you expect the crank to show at least some discoloration?
 
I can't tell in the pic if the crank journal was effected too but the bearing getting that hot is the issue .
Crank is a big piece of steel too , it can absorb a lot of heat .
When the con rod bearing runs hot the heat concentrates and it's always the con rod that shows it .
 
I can't tell in the pic if the crank journal was effected too but the bearing getting that hot is the issue .
Crank is a big piece of steel too , it can absorb a lot of heat .
When the con rod bearing runs hot the heat concentrates and it's always the con rod that shows it .
Sure, the rod is less mass so it will get hotter, but the other parts should show something. At the least you should be able to see part of the roller - those should certainly be discolored if the rod got that hot.
 
It would be odd why only that bearing got that hot and none of the others. If there was a lean situation at some time then it should have showed on the piston, possibly the jug and certainly the upper rob bearing yes ?
 
Yes it would but are you certain they had not been changed ? , I'm not going to tell you that the bearing is going to fail , it could run for some time like that but it is what it is . You purchased it off Ebay , someone likely did a repair to flip it .
In my tenure at Stihl I never saw a factory blue case hardened con rod , they did not do that . That con rod bearing is the first to get hot if there is a severe lean seize (think excessive RPM's) and the outcome is generally as pictured . If it gets to the point were that bearing does actually come apart then you might see a little discoloration in the crank but it was very rare if I recall correctly usually some bearing cage material melted onto the crank would be what you would see .
 
I had a 064 rod that looked like that. I put it together. It never did go kaboom. It was rode hard and put away wet.

Again , it may last for some time , it's a crap shoot . Is the bottom end shot?.....well sort of is about the only way you can put it .

You have to realize of any bearing in that engine that con rod bearing is doing most of the work and taking most of the abuse . Piston pin bearing has it easy......just a rocking motion , crank bearings are big and can bleed heat off to the case but that con rod bearing , it's doing the hard work , spinning , G forces , pressure , heat and it's not all that big . That's why you will see it heat up first and usually be the bearing that fails under lean conditions . Crank bearings , usually chain too tight or operator snapping the chain brake on all the time , pin bearing they can get hot too but rarely like the con rod bearing .

A good book for reference is the "Stihl engine failure analysis guide" which I think can be found with a google search .
 
I have seen dozens of 440s and 460 that look just like that and none of them failed. Take that for what it is worth. Good luck!
 
Just for some insight into what goes on with the con rod bearing here is a good write up that explains it way better than I could at a technical shop school........

Excessive RPM. Big end bearings can fail in minutes if subjected to excessive RPM. The reason is: During regular operation the rollers (in the big end bearing) roll on the outside surface of the crankshaft journal and on the inside surface of the connecting rod. A light film of mix oil coats the bearings with every rotation the crankshaft makes. This bath of oil (and fuel) lubricates the bearing, which removes friction and keeps the bearing running cool. When the engine is subjected to excessive RPM (like limbing with the throttle wide open), the rollers roll as fast as they can and then start "skating." This skating or sliding activity scrapes away the cushion of oil on the bearing surfaces. The bearing gets hot instantly. If the engine speed does not come down to where the rollers can roll again, it fails quickly. Even if the speed returns to normal, the bearing sustains some damage.

Keep the RPM's down , I usually go 500 below saw spec to allow for fluctuations from conditions that can change the setting .
 
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