greendohn
firewood hack
I was gonna' say H2o caused the pitting ??
Name This Damage
- Thread starter Mastermind
- Start date
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tickbitintn
ArboristSite Operative
piston trashed... cyl looks pretty clean, did you clean it up or was that how it was ???
it got pretty warm around that ring land on the ex side anyway, detonation, low quality fuel probably the culprit....
pre-ign usually creates a hot spot and burns a hole in piston... (right ? or do i have that backwards)
it got pretty warm around that ring land on the ex side anyway, detonation, low quality fuel probably the culprit....
pre-ign usually creates a hot spot and burns a hole in piston... (right ? or do i have that backwards)
HuskStihl
Chairin'em for the sound
Midget with a ball peen hammer?
Detonation. Blah blah blah propagation flame front blah blah blah low octane
Detonation. Blah blah blah propagation flame front blah blah blah low octane
Hard to type when yer hangin' upside down?
Mastermind
Work Saw Specialist
I'd cleaned up the jug already, was about to cut the squish and thought I'd take some pics.
Yeah pre-ignition in a two-stroke is very destructive....this is just a case of ****** fuel.
Mastermind
Work Saw Specialist
I just finished cutting that jug, gonna go hang again......now.
And yet water injection is common in many engines. I built a system for my '66 mustang in the early '80s so I wouldn't have to buy premium fuel.
I'll go with bad gas. Lots more can happen to it than just ethanol/water.
I'll go with bad gas. Lots more can happen to it than just ethanol/water.
fearofpavement
Trying them all
detonation gets my vote. In water cooled engines it makes noise (pinging) but in air cooled engines it can pack them in. So since ignition timing doesn't change much on chainsaws, the "bad gas" votes would be correct as well since octane is primarily an "anti-knock" index.
Stihl working hard
Is it Friday yet
Definitely running with bad gas
BINGO!
WHSH
ArboristSite.com Sponsor
I assume that some one did it on purpose so I could have income.
I just rebuild as saw that had that but 5x worse. Just under the decomp there was a crator in the piston, along with the pocked squish band and piston crown. The saw was modded before (not by me) with a pop up and base cut, it looked like compression north of 200psi In my case I assumed a very lean condition, crap low octane e10 fuel and the decomp rough edges caused detonation a due to the wicked high temps. I may be wrong thats my guess
I just rebuild as saw that had that but 5x worse. Just under the decomp there was a crator in the piston, along with the pocked squish band and piston crown. The saw was modded before (not by me) with a pop up and base cut, it looked like compression north of 200psi In my case I assumed a very lean condition, crap low octane e10 fuel and the decomp rough edges caused detonation a due to the wicked high temps. I may be wrong thats my guess
glock37
Addicted to ArboristSite
ignition advanced to far with bad fuel
how is the coil edge jap ? if no points and no plate ?
Randy didn't my 041 super have a piston with those marks on it but the cyl was ok
and it has a plate and points ,timing is important with todays fuel
how is the coil edge jap ? if no points and no plate ?
Randy didn't my 041 super have a piston with those marks on it but the cyl was ok
and it has a plate and points ,timing is important with todays fuel
Definitely detonation.
The cause could be many things, but the pitting shows the truth.
I really doubt if it was from running too high octane, higher octane fuels burn slower, and that is a fact.
I have a 143 that looks just like that, it will still hurt you if you aren't real serious pulling it over.
The cause could be many things, but the pitting shows the truth.
I really doubt if it was from running too high octane, higher octane fuels burn slower, and that is a fact.
I have a 143 that looks just like that, it will still hurt you if you aren't real serious pulling it over.
Nope. Set too lean from the factory.
Don't know about 'perfect'.
Detonation can and will damage bearings, even caged needle bearings.
It is quite the destructive reaction.
Trx250r180
Saw polisher
Have fun with it boys.........what causes this?
i see a decomp hole right there ,the valve still good ?
UpOnTheHill
ArboristSite Guru
Either cavatation or water turning to steam (flashing). That's my guess anyway. I'm an hvac guy and that same pitting can be caused by oxygen being released from water because system pressures aren't high enough. I'd say water in the fuel!
labdad
ArboristSite Operative
Besides pinging we used to call it spark knock, you know back in the good old days....
Bringing this to the top as it is good tech.
The cause is pre-ignition. The reason it happens on the exhaust side, is because piston temperature is highest due to the flow of exhaust across the piston. So now it has a "hot spot" and a fresh charge of air and fuel, what happens is the hot spot ignites the charge over itself causing multiple flame fronts to collide in that isolated area. This is what takes out those little craters. If you Google cavitation damage you will see similar damage.
I find that water in the fuel has more of a cleaning effect on the combustion chamber... as the damage is not as localized.
The cause is pre-ignition. The reason it happens on the exhaust side, is because piston temperature is highest due to the flow of exhaust across the piston. So now it has a "hot spot" and a fresh charge of air and fuel, what happens is the hot spot ignites the charge over itself causing multiple flame fronts to collide in that isolated area. This is what takes out those little craters. If you Google cavitation damage you will see similar damage.
I find that water in the fuel has more of a cleaning effect on the combustion chamber... as the damage is not as localized.
Can't believe the bearings are good. Had and old moped that I rebuilt for my daughter that did the same exact thing when the cage on the crank end rod bearing self destructed. What really $u@#&d was that I replaced everything else in the bottom end. When you talk about "bad gas", ethanol with water soluble in the mix can accumulate in the case and rust/pit the crank races. Looking back at the moped rebuild, there was rust on the crank. I suspect the pitting either galled the races or prevented the rod bearing from spinning properly. Exuberant installation/removal force on the piston pin can damage the same. Its the one bearing that you really can't see to inspect and some slop is tolerable.
All this said, something got "gargled" other than gas
All this said, something got "gargled" other than gas
