395xp 2018 big end bearing failure with pics

[kneedeepinsaws]

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

Can you take a video of the “play?”

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

+1. That piston will tell us a lot.

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.

Upon more examination i dont believe i ever did remove the base gasket. There is no evidence of it and every time i do it, its messy. You can still see the machining marks from the factory and the gasket lettering.

anyways here is the vid

Here are some more shots of the piston top and a clearer shot of the inside top of the cylinder

 

[jacob j.]

Grab the rod with your fingers, slide it over against one side of the rod journal, and see if you can get any up and down movement at all with your fingers.

 

[Moparmyway]

Looks like a lose flywheel, not a bad bearing

Tighten that nut in the middle

 

[kneedeepinsaws]

Grab the rod with your fingers, slide it over against one side of the rod journal, and see if you can get any up and down movement at all with your fingers.

This is harder than it sounds. But i believe i am not Feeling any play.

Looks like a lose flywheel, not a bad bearing

Tighten that nut in the middle

I wish that were true!

 

[jacob j.]

This is harder than it sounds. But i believe i am not Feeling any play.

I'm thinking your crank is probably ok. There's always going to be a little bit of "free play" when turning the flywheel of a modern saw engine. You have to have some
give for an engine to last in standard operating conditions.

The older saws were worse - in fact, McCulloch used main bearings in their saws for years that didn't have cages. They just had enough ball bearings in them to keep
everything snug, and those engines would run for hundreds of hours that way.

 

[kneedeepinsaws]

I'm thinking your crank is probably ok. There's always going to be a little bit of "free play" when turning the flywheel of a modern saw engine. You have to have some
give for an engine to last in standard operating conditions.

The older saws were worse - in fact, McCulloch used main bearings in their saws for years that didn't have cages. They just had enough ball bearings in them to keep
everything snug, and those engines would run for hundreds of hours that way.

Piston slap then?
Piston is 55.96mm on the skirt all the way up

 

[Mattyo]

That big end is likely not the source of play.

The flywheel seems to be solid on the shaft because the shaft is moving with the flywheel.

Keep looking.

 

[Mattyo]

Make sure the clutch is off ....oiler is off ..bare pto shaft. Bare flywheel shaft. Then check.

 

[huskihl]

1.2mm rings in a 1.5mm ring groove?

You can maybe get a better look at that bearing play through the intake. I had a brand new 3120 here with 1/8” of fw rotation of slop in the rod bearing

 

[kneedeepinsaws]

That big end is likely not the source of play.

The flywheel seems to be solid on the shaft because the shaft is moving with the flywheel.

Keep looking.

Well i pulled the boot so i could maybe see whats going on.
I pulled the clutch but i left the flywheel on only cause its so much easier to get leverage to do this. On top of that the flywheel is not the issue here, it is in sync with the clutch side and is tight.

inside the intake port i can see the rod moving up and down but the piston is not. I had to sit there for a good ten minutes and look with a flashlight. To confirm such a minute detail, i put a flatblade screwdriver on the rod and did the small back and forth rotation of the flywheel. I can feel the rod moving with the screwdriver, I am now sure that the play is in the piston pin bearing.

gonna pull the jug again and put the piston back on and try some more techniques to verify it is the piston pin or small bearing.

 

[Al Smith]

Just a reminder when you set TDC with a degree wheel you feel for movement one direction to the other and set it in the middle .So it's not unusual to have a little slop in the bearings /rotating assembly .
Plus remember it's a two cycle .For all intents the piston is under compression or power all the time during it's rotation .
If you already have it apart just get a new pin bearing and be done with it .A pin bearing is relatively inexpensive .

 

[BuckthornBonnie]

I'm thinking your crank is probably ok. There's always going to be a little bit of "free play" when turning the flywheel of a modern saw engine. You have to have some
give for an engine to last in standard operating conditions.

The older saws were worse - in fact, McCulloch used main bearings in their saws for years that didn't have cages. They just had enough ball bearings in them to keep
everything snug, and those engines would run for hundreds of hours that way.

Yep. Little Homelites with needle bearings and thrust washers move so much it makes ya wonder how they last 35years (low rpm, decent design).

It’s tough to describe some saw issues online. It’s tough to diagnose issues if the only information you have is from the internet. Crank play, P/C clearance, bearing install, etc. all have nuances you get by looking at a lot of parts and seeing what is good/bad. Experience fixes saws, not an expedited mechanic’s course online.

All too frequently I see bad advice on the forums that snowballs. It somehow propagates on its own! A good example is a guy on FHC who destroyed his 391 by replacing oem “good” bearings with AM junk. It was a sad thread and only one example of many.

 

[SpaceBus]

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!

Normally I use my 395 for milling, but I'm waiting on parts. Been running my 460 with 40:1, but I run the high jet rich enough to get no four stroking. Should I run the saw a bit more on the lean side? I just can't afford to break any more equipment right now.

 

[Ford3000]

Normally I use my 395 for milling, but I'm waiting on parts. Been running my 460 with 40:1, but I run the high jet rich enough to get no four stroking. Should I run the saw a bit more on the lean side? I just can't afford to break any more equipment right now.

If your saw is not four stroking, are you not already too lean.

 

[Al Smith]

Just as general info the only crank bearing I ever saw that actually failed was a Dolmar/Makita with extremely high hours which had spit part of a bearing from the cage loose .Easy enough to find because it was rattling around in the crankcase .To repair same because it's a pressed together assembly is cost prohibitive .
However on the subject it is not all that difficult to determine if you have ball a main bearing going bad .If a tiny piece of hard grit gets lodged in the cage it can spall off the chrome then over time it will only worse until it hangs up .You about need the top end removed then feel for a hang up which could be slight .Then if replace both bearings and seals and it will probably run for years .

 

[Mattyo]

I agree... this would have already been split. With new bearings and seals.

Evidence of big end failure would be seen with funky colors and pieces missing...and debris elsewhere.

Just sayin

 

[Al Smith]

Just a word .Because the crankshaft is a heat shrink fit more often than not it will display some bluish coloration from the induction heater used in the process .

 

[kneedeepinsaws]

I agree... this would have already been split. With new bearings and seals.

Evidence of big end failure would be seen with funky colors and pieces missing...and debris elsewhere.

Just sayin

I split it last night.

i checked the fsm, its is incredibly vague. Does indicated that any axial play is good and radial play is no good.
I cleaned the crank and the rod spins very freely. There is the most minute amount pf vertical play, the problem is trying to check it perfectly straight up and down.

 

[Al Smith]

It's nearly impossible to trouble shoot anything over the internet and the best anybody could do is an educated guess .This rattle or whatever it is could be anything .It might be a worn out anti vibration mount which I have seen .

 

[srcarr52]

It's nearly impossible to trouble shoot anything over the internet and the best anybody could do is an educated guess .This rattle or whatever it is could be anything .It might be a worn out anti vibration mount which I have seen .

Loose clutch springs.