MS461 failure analysis help

[Woodslasher]

I got this toasted 461 awhile ago and I'm getting ready to rebuild it but I've run into a problem. Based off of Madsen's piston failure analysis chart and my personal knowledge of the saw's past life I'm guessing either dirt incursion or bearing failure caused the pictured marks on the piston, but I'm not sure which and was hoping one of you might know. If it is a bearing failure, how do I tell which one it is?

 

[Woodslasher]

Also, should I replace the crankshaft along with the main bearings if the damage is from a failing bearing?

 

[TLG]

I would suggest looking for broken or pieces of missing bearing cages. Also and inner or outer race's or fragmentation's of rollers, or needle bearings. [Surface Hardness meeting it's limitations].This would include rod, mains, and wrist pin locations. If you slide the conn rod to either side it helps with the inspect.

 

[sean donato]

I would personally day bearing failure as well, but like stated above there should be some obvious damage to one (or more) of the bearings. And to me the intake side doesnt have that matte finish that you see with dirt ingestion. You should also see debris in the carb and intake tract if it was eating dirt.

 

[stihl86]

Sometimes a hi- def picture looks deceiving, but I don’t know about any brg damage.
Usually there’s more damage than you have. The piston looks very strange.
The top, yes, possibly. But the sides look more like it got fed steady supply of dirt.
Or something very abrasive. Which can lean out a saw, causing the ex side damage.
Wood dust could do it. It doesn’t look like dirt (earth).
It is also possible, a large mount of moisture in the fuel.
Cant say I’ve ever seen that kind of damage.

Can you feel anything in the bottom of the case?

 

[MacAttack]

I think if a bearing was chewed up bad enough to do that, you would easily feel it when you turn the crank or check the ends for radial play. I'm personally skeptical that this was from a failed bearing, I think it sucked something in.

 

[Ozhoo]

 

[huskihl]

Piston looks like it was straight gassed. The dents on top could be from a bearing but they’re usually more pronounced and there should be evidence vertically on the piston near the transfer ports.

 

[rupedoggy]

Can't prove it one way or the other but my money is on a circlip failure, Maybe just the tang end but look at how the piston is damaged between rings. Something scrapped by there. The little wire danced around on top of the piston some. There is additional damage from heat also.

 

[Woodslasher]

Well, I am officially the dummy! I looked closely at the case bearings and noticed the races were gone in both sides. I guess that answers that. The crankshaft seems fine, though.

 

[MacAttack]

Wow....so does the crankshaft have all kinds of play? It must not turn very smoothly

 

[sean donato]

They dont always turnover bad if most of the balls are there and it's just the cage that flew apart. At any rate, glad you found the issue. Now you know your doing a full rebuild on it.

 

[Mad Professor]

They dont always turnover bad if most of the balls are there and it's just the cage that flew apart. At any rate, glad you found the issue. Now you know your doing a full rebuild on it.

From the picture of the flywheel it looks like the crank was flopping around , I wonder if the pickup on the coil is damaged too?

 

[MacAttack]

From the picture of the flywheel it looks like the crank was flopping around , I wonder if the pickup on the coil is damaged too?

I noticed that too, the laminations took a hit, that crank must have at least .030" slop in it to do that...

 

[Woodslasher]

Wow....so does the crankshaft have all kinds of play? It must not turn very smoothly

The big end bearing seems fine but yeah, the crankshaft seems pretty sticky. If the coil got nicked do I need to replace it? This is the first saw out of all the ones I’ve worked on that had the bearings blow up so I don’t know how to deal with the fallout yet.

 

[MacAttack]

The big end bearing seems fine but yeah, the crankshaft seems pretty sticky. If the coil got nicked do I need to replace it? This is the first saw out of all the ones I’ve worked on that had the bearings blow up so I don’t know how to deal with the fallout yet.

I've had coils in which the metal laminations were banged up, swelled with rust, etc that still worked. Theyre pretty tough so it will probably still spark as long as the potted coil part is not damaged badly.

 

[SteveSr]

I noticed that too, the laminations took a hit, that crank must have at least .030" slop in it to do that...

Wow! Beginning to look like a parts saw instead of a rebuild candidate.

Put up some good pics of the magnets on the FW and the coil pole pieces. I suspect that if there is significant material missing from either you are likely looking at replacements for both components. The magnetic circuit was designed to work at a specific flux density set by the area of the pole pieces in the coil. The field strength is set by the gap. While it may still fire the timing will likely be wrong or inconsistent.

 

[sean donato]

So far, other than possibly the coil, it looks like a standard rebuild to me. Parts are cheap and plentiful for these saws.

 

[rupedoggy]

So far, other than possibly the coil, it looks like a standard rebuild to me. Parts are cheap and plentiful for these saws, the 357xp interchanges parts as well. I'd fix it...

A Husky 357 interchanges with a 461 Stihl? I don't think so. Mike

 

[sean donato]

A Husky 357 interchanges with a 461 Stihl? I don't think so. Mike

ha, yeah, I was reading the 359 husqy thread before I read this one. Yeah deffinatly does not interchange.