Can anyone explain this?

[pioneerguy600]

For the sake of $25. I would just put a new piston in it.

 

[monk34]

For the sake of $25. I would just put a new piston in it.

i didn't think a piston would be so cheap. Would the cylinder need replaing too? there are a few dents in the top of it

 

[pioneerguy600]

The cylinder is likely ok, the ball bearing would be too big to get between the cylinder wall and piston and the rounder edges of a bearing wouldn`t cause scoring like sharp edged metal bits. I would closely check out the main radial bearing in the saw though before installing any new parts.

 

[windblown]

i didn't think a piston would be so cheap. Would the cylinder need replaing too? there are a few dents in the top of it

If it were me and I wanted the saw to run right and not give me trouble I would replace the cylinder as well. The top of the cylinder been hammered and possibly not sound structurally, beyond that all the dents will almost certainly have some negative impact on flame propagation and the saw may be more prone to detonation and pre-ignition.

Now if you just want to see if it will run at all and don't care if it blows as an experiment then have at and let us know how it goes! I POS B&S motor in a riding mower once that dropped a valve seat. With nothing to lose I took the head off, used a punch to re-seat the valve seat, slapped it back together and the dang thing ran for 2 months before going "poof". Meh, 2 free months of use before selling it for parts. Worked out ok.

 

[9050LX]

Love to see it run, make a destruct video, kind of like a washing machine on a 240Volt variac.Just kidding, bet it runs OK if all the bearings are intact.

 

[monk34]

If it were me and I wanted the saw to run right and not give me trouble I would replace the cylinder as well. The top of the cylinder been hammered and possibly not sound structurally, beyond that all the dents will almost certainly have some negative impact on flame propagation and the saw may be more prone to detonation and pre-ignition.

Now if you just want to see if it will run at all and don't care if it blows as an experiment then have at and let us know how it goes! I POS B&S motor in a riding mower once that dropped a valve seat. With nothing to lose I took the head off, used a punch to re-seat the valve seat, slapped it back together and the dang thing ran for 2 months before going "poof". Meh, 2 free months of use before selling it for parts. Worked out ok.

Yeah, you have a good point. In my case, I don't really want to put much money into a 40 yr old saw so I'll probably just replace the piston or maybe try to salvage the damaged one. I'll try and remember to make an update on it later. Cheers!

 

[KASH]

Put it back together and run it .If it doesnt then fix it.I had a 73 Arctic Cat snow mobile with a 440 twin Kohler motor which was running beautiful one day I was changing a spark plug and noticed the top of the piston looked odd.I pulled the head it looked not quite as bad as yours that was 25 years ago and the machine is still running beautiful.
I have restaked the valve seats on many 4 stroke motors it is real common on Tecumseh engines.
Kash

 

[Smitty Smithsonite]

I've only seen ball bearings in crank bearings, so one must've got sucked through the transfer port and hammered the pee out of that piston! Looks like someone went wild with an air hammer and a pointy bit attachment.

If that's what happened, then the saw must've been super noisy prior to this discovery. Crank bearings bad enough to spit a ball out make a HUGE racket - enough to hurt your ears more than the exhaust note. Hugely noticeable at idle. Normally they seize long before that from the unmetered air entering through the blown out crank seals they caused. That's a strange one for sure. You must've recognized it was running leaner and leaner, and kept unscrewing the high mixture screw.

 

[Screwbolts]

It is so very self evident that the engine ingested a round piece of very hard metal while running!!! LOL

 

[monk34]

I've only seen ball bearings in crank bearings, so one must've got sucked through the transfer port and hammered the pee out of that piston! Looks like someone went wild with an air hammer and a pointy bit attachment.

If that's what happened, then the saw must've been super noisy prior to this discovery. Crank bearings bad enough to spit a ball out make a HUGE racket - enough to hurt your ears more than the exhaust note. Hugely noticeable at idle. Normally they seize long before that from the unmetered air entering through the blown out crank seals they caused. That's a strange one for sure. You must've recognized it was running leaner and leaner, and kept unscrewing the high mixture screw.

yea it was running lean and it also wouldn't run for more than a few minutes

 

[Mike Ray]

n
saw similiar thing some where (maybe on this site) when I saw similiar thing on my stihl 023 but not as bad, when I was trying to figure out why it is so hard to pull the starter. The marks aren't as large and are in a straight line in different sizes. don't know when it happened as I bought it used, but saw runs amazingly well. The post I saw suggested bad gas as in water contamination as fuel not exploding as it should and you can't compress water. pretty sure I saw it on this site his piston looked similiar to this.also note the craters aren't the same size

 

[9050LX]

So what part of the engine is missing a hard round object?

 

[monk34]

So what part of the engine is missing a hard round object?

i think it came from the choke adjustment. There was a little ball bearing to keep the choke in position. I remember taking the choke out and losing the bearing. I guess it somehow got in the combustion chamber. What are the chances of that lol!?

 

[TRTermite]

For the sake of $25. I would just put a new piston in it.

AND FRAME/HANG THAT PISTON as a TROPHY FIND

 

[Oletrapper]

I'm not very bright sometimes so if you care about this saw Id fix it right. Cold-hammering aluminum with a ball bearing probably put invisible cracks in it.

To me, the piston already appears to be cracked in the center. jmho OT

 

[Oletrapper]

i think it came from the choke adjustment. There was a little ball bearing to keep the choke in position. I remember taking the choke out and losing the bearing. I guess it somehow got in the combustion chamber. What are the chances of that lol!?

Ha Ha, Pretty good evidently. jmho OT

 

[Screwbolts]

There you have it! the ball bearing used as the choke shaft detent.
Self evedent it was a round ball