Calling All Saw Detectives

[Yotaismygame]

I don't know- maybe your local 70 year old is as fit as a buck rat and can start a reasonably big saw, slam it to WOT and sprint to the log before the saw is warm as suggested by someone that has seen somewhere between six to ten pistons total since first taking a wrench to a powerhead, but that usually displays as a thin concentrated strip of scoring width wise.
Straight gas can migrate around the piston to score the intake side- but then I would expect to see dry gritty underside internals of the piston and dry crankcase. Is there any wallowing of the inside of the piston wrist pin bosses where they would wear against a dry con rod top if it was severely lean fuel mix?
Cutting firewood is way more taxing than felling, if the owner is anything like me, the saw is run pretty much WOT for the entire fuel tank as you work down the log, fill it up and do it again....... which takes us back to overworked/overtaxed heat seize.
Do you know the species he was last cutting, size of the log, duration of the session, weather conditions?

At the moment I do not know the exact details.

 

[farmguywithasaw]

If you look at the top of the piston there is some pitting wich is a indication of detonation. It is a pop up so if running ****** gas it could happen

brain dead...………..

 

[Jasent]

Definitely looks like crap gas to me and heat. probably runs it till it’s dry before refuel. Running out of fuel at wot on a hot saw can be pretty rough on things. Especially if it’s often. What’s the squish?

 

[Yotaismygame]

Definitely looks like crap gas to me and heat. probably runs it till it’s dry before refuel. Running out of fuel at wot on a hot saw can be pretty rough on things. Especially if it’s often. What’s the squish?

I set majority of saws to .020 pending size.

 

[Yotaismygame]

I'm really thinking it was a combination of user error, tune, and fuel. When he called me to tell me the saw was difficult to start cold I figured it needed more fuel based off what he said. Not sure if he ever adjusted it.

 

[frank_]

If you look at the top of the piston there is some pitting wich is a indication of detonation. It is a pop up so if running ****** gas it could happen

yes classic signs of det when you zoom in
and i agree on the high compression and stale fuel theory

 

[drf255]

Sure just looks lean to me. Ported saws with more open mufflers seem to have less of a buffer window on tune, one of the reasons I prefer the never autotunes ported for an inexperienced saw runner. Coulda been different mix ratio, oils, etc... I have personally seen certain oils at lower mix ratios (by number) lean a saw out because the mix was more viscous.

Knowing how to tune by ear should be a prerequisite to owning a modified saw. Many don’t get it, which used to include me. I only learned the errors of my ways when I started reading this forum.

 

[hillwilliam]

A high-speed jet open only 3/4 turn isn't uncommon at 10,000 ft. altitude, depending on the saw. But it might have been pretty lean where he was.

Did you get a look at the chain he was using. It may tell you a lot.

 

[Yotaismygame]

A high-speed jet open only 3/4 turn isn't uncommon at 10,000 ft. altitude, depending on the saw. But it might have been pretty lean where he was.

Did you get a look at the chain he was using. It may tell you a lot.

Chain was good. I cut with it after installing a new piston. Saw runs good. We’re only at couple hundred feet here. Owner admitted he never adjusted the tune after I rebuilt it. I run 40:1 he runs 50:1. From what I can tell it was the tune and situation. No other signs came up

 

[hillwilliam]

Looks like you must have it figured out. Yup, 40:1 with good oil works well at these elevations and in some pretty gnarly saws.

 

[Yotaismygame]

Looks like you must have it figured out. Yup, 40:1 with good oil works well at these elevations and in some pretty gnarly saws.

Yeah really hard to say. I was certain I would find an air leak or clogged inlet in the carb or something of that nature but nothing.

 

[Jacob J.]

I'm with the bad gas crowd on this one. I had a customer blow up a freshly rebuilt 288 by using his old lawn mower gas to make mix for the saw. The lawn mower fuel had been sitting
for about four months. The damage looked pretty much the same as the piston in your pictures. I was able to salvage the cylinder.

 

[Yotaismygame]

I'm with the bad gas crowd on this one. I had a customer blow up a freshly rebuilt 288 by using his old lawn mower gas to make mix for the saw. The lawn mower fuel had been sitting
for about four months. The damage looked pretty much the same as the piston in your pictures. I was able to salvage the cylinder.

He did say he cycles through fuel frequently. But here's a curve ball. Another local customer of mine who is friends with the 371 owner borrowed his saw for a day right before the top end burned up. Ironically this same guy toasted the top end on his own Makita 7910 which I had sold him a few years ago. I ended up buying that makita back but have yet to look at it. Makes me wonder if that guy had bad gas.

 

[Bob Hedgecutter]

He did say he cycles through fuel frequently. But here's a curve ball. Another local customer of mine who is friends with the 371 owner borrowed his saw for a day right before the top end burned up. Ironically this same guy toasted the top end on his own Makita 7910 which I had sold him a few years ago. I ended up buying that makita back but have yet to look at it. Makes me wonder if that guy had bad gas.

Your "curve ball" is more than likely your culprit then.
NEVER loan out your saw and NEVER run someone elses mix through it. Murphy will appear and ruin a good saw in a tanks worth of fuel.
An old tree feller once said to me when I broke a recoil spring and asked to borrow his #2 saw- "Would you loan out your wife? No, me neither- but I would loan her out before I loaned my saw out!"

 

[cranman1951]

I never loan out any saw I care about, or use someone elses mix.

 

[hillwilliam]

Now it's sounding like the "curveball". I certainly agree with the above about never loaning a saw. I've seen strong, healthy saws destroyed by borrowers.

I'm no kind of rich, but I've given a lot of saws away. I gave a really good saw to my best friend, but I'd never let him borrow one.

 

[HarleyT]

Lean seizure...