395xp 2018 big end bearing failure with pics

[kneedeepinsaws]

Noticed when I ran this saw earlier it literally sounded like a tractor at idle... didnt think too much of it and passed it off as just big saw noise...
Few hours later I decided well ill pull the flywheel cover off and just see what i can feel spinning the flywheel. Sure enough when i lightly rotates the flywheel back and forth I could hear a clicking noise coming from inside. Made sure it wasn't the clutch bearing or something and confirmed it wasn't so i took the top end off to check out what was happening.

There was a slightly amount of play given the right rotation of the crank with the piston on, so pulling the piston off i confirmed the big end bearing has up and down play
It also is making noise when rotated, something is grinding in there...

Too bad, i was boasting about how this saw is the most reliable saw ever and this happens. Looks like the gods were not smiling down on me...

this saw was run 32:1 with maxima k2 oil for 3/4 of its life. It was my primary milling machine until i replaced it with a 3120. The other last 1/4 of its life before i retired it early this year was 40:1 with the same oil.
Inside is really clean, this saw has never been apart before from what i can remember and the intake is immaculately clean. However the scratches on the intake indicate some kind of particles got in due to the scratching. Big end shows no sign of overheating as their is no discolouration.

if you look at the photos you can see the right side of the cage has a polished look to it where you can tell it was starting to rub in the rod. The left side, nothing really.

I now have all the tools to do this job, including the seal pullers. The splitter from the 372 will work on this saw according to the part number of the tool.

if anyone has any input or ideas on failure causes please chime in.

 

[kneedeepinsaws]

Some
Pics of the piston pin, bearing pin ghosting on the pin. Probably normal but ill see what you guys think. Included is a shot of the intake side of the cylinder

 

[andyshine77]

The bottom end honestly looks a little dry, was there a nickel-sized pool of oil in the bottom of the case when you pulled it apart? Also was she tuned for milling? As you alluded to, if the bottom in wasn't getting enough oil you normally see some bluing.

I really don't I know, besides the bottom end looking a bit dry, everything looks good really good. Try taking the flywheel off and see how it feels when spinning. Make sure the play you're feeling isn't side to side, and just radial. if tuned nice and rich for milling, pretty much any oil should be good enough and K2 is a great oil, but than again milling is crazy hard on saws. I'm not 100% convened the bering is bad. Try it with the flywheel or coil off the saw. Also flush the case with some fuel mix, spin her around with the mix in there, sometimes a small chunk will get in there during disassembly.

Best of luck.

 

[kneedeepinsaws]

The bottom end honestly looks a little dry, was there a nickel-sized pool of oil in the bottom of the case when you pulled it apart? Also was she tuned for milling? As you alluded to, if the bottom in wasn't getting enough oil you normally see some bluing.

I really don't I know, besides the bottom end looking a bit dry, everything looks good really good. Try taking the flywheel off and see how it feels when spinning. Make sure the play you're feeling isn't side to side, and just radial. if tuned nice and rich for milling, pretty much any oil should be good enough and K2 is a great oil, but than again milling is crazy hard on saws. I'm not 100% convened the bering is bad. Try it with the flywheel or coil off the saw. Also flush the case with some fuel mix, spin her around with the mix in there, sometimes a small chunk will get in there during disassembly.

Best of luck.

Thx andy.

wasnt blaming the oil, its good stuff. Just wanted to point out she was well taken care of.
When milling she would 4 stroke in and out constantly, for milling i consider this rich while still making good power. I could be mistaken.

Will split the cases shortly and see where that goes, thanks for your input!

 

[andyshine77]

Thx andy.

wasnt blaming the oil, its good stuff. Just wanted to point out she was well taken care of.
When milling she would 4 stroke in and out constantly, for milling i consider this rich while still making good power. I could be mistaken.

Will split the cases shortly and see where that goes, thanks for your input!

It just looked a little dry down there lol. Try flushing the bottom end out, and try and spin her with no flywheel. If it does have play, obviously this will do nothing, but it's free and worth a shot.

Sux these saws are pretty bullet proof, seeing the dry bottom end, would make me want to run something like Motul 800 when milling. But really it likely wasn't caused by the oil.

 

[huskihl]

What’s the top of the piston look like? It looks like something got in there and was hammering the squish band. It will take out a crank in short order

 

[Wilhelm]

Having been run milling is all I needed to read, ran hard and gave in.
Could have ended much worse.

 

[BuckthornBonnie]

Can you take a video of the “play?”

 

[BuckthornBonnie]

What’s the top of the piston look like? It looks like something got in there and was hammering the squish band. It will take out a crank in short order

One pic has that look... I don’t know if it’s an illusion or not.

+1. That piston will tell us a lot.

 

[Mattyo]

Every big end bearing failure I've seen on 394 288 cranks ....the crank looks much worse than that. Usually there's pieces of cage missing...needles missing. I would like to see a video of the play too. Your bottom end looks pretty clean to me.

 

[andyshine77]

What’s the top of the piston look like? It looks like something got in there and was hammering the squish band. It will take out a crank in short order

Good eye, if it's actually dented you're right.

 

[andyshine77]

Every big end bearing failure I've seen on 394 288 cranks ....the crank looks much worse than that. Usually there's pieces of cage missing...needles missing. I would like to see a video of the play too. Your bottom end looks pretty clean to me.

I agree, from the pic the bearing looks fine.[emoji111]

 

[srcarr52]

Detonation will kill a bottom end bearing.

 

[flyin'chips]

To me it looks like out of focus high lights are "expanding" in the squish band making it look dented. In the last photo of the cylinder the top appears normal.

Big end bearing looks like it has more wear on flywheel side. Could it be caused by the saw being on it's side allways in the same orientation when milling and gravity pushing the rod?

 

[kneedeepinsaws]

Ohhh boy i was thinking about this today while working... i bet i got rid of the base gasket a while back and ran it. As you can see the gasket is installed but i have a feeling that this was not always the case. I probably put it back in changing my mind.

I aint trying to pass the buck, i really dont remember but there was a time when i was removing base gaskets from saws a while back. I am pretty sure i *f-worded this one up...
Its gonna cost me!
When i get home ill get more photos but i recall a lighter coloured area around the edge of one side of the piston. This is probably where it made contact when heating up and not when cold in which the top of the cylinder is not square with the cylinder wall thus its only on one side.

shame shame

 

[kneedeepinsaws]

I will have to check and see if there is any evidence of gasket maker that will confirm what i am thinking...

 

[Mastermind]

That’s the least failed looking bearing failure I’ve ever seen.

 

[kneedeepinsaws]

That’s the least failed looking bearing failure I’ve ever seen.

It has play, ill prove it when i get home. Thing sounds literally like a tractor at idle

 

[Mastermind]

It has play, ill prove it when i get home. Thing sounds literally like a tractor at idle

You have no reason to prove anything to me.

I'll just move on.

 

[redlight066]

Main bearing, big end bearing.... potato, potahhto