Sometimes you wish you'd never looked...

[the crafty weasel]

Had to change the anti vibe mounts and inlet gasket the other day on the makita/dolmar 5200i in work, so thought I'd pop the barrel off to see what the bore was like. Wish I hadn't now. Still got plenty of power though, which is surprising.

 

 

[Graham]

Is that bore Nikasil lined? Might clean up if it's just deposits. New piston and job done. Alternatively...if it ain't broke don't fix it and just carry on:001_smile:

[the crafty weasel]

I just put it all back together and the saw still runs fine. Hoping to part ex it this year for a Makita 5301, so if it runs ok until April I'll be happy.

[Sideleaner]

I would suggest to hone the cylinder and replace the piston. It is clear that the piston is not aligning straight in the cylinder so it is at it end.

Not replacing it is just going to cause a worse wear.

Just curious, what 2stroke oil did you use and which mixture ?

 

Pascal

[the crafty weasel]

I use Stihl Two stroke oil, and the photo doesnt show it too clearly, but its not lean scuffing, something has gone into the bore, had a bit of a party in there then left again. the air filter was split when i started working there as well, which might explain something.

[tree_beard]

I use Stihl Two stroke oil, and the photo doesnt show it too clearly, but its not lean scuffing, something has gone into the bore, had a bit of a party in there then left again. the air filter was split when i started working there as well, which might explain something.

 

a foreign object would likely cause more damage to the intake side and top of the piston... seeing as how you posted a pic of the exhaust side i'm assuming that is where the worst of the scoring is, so i'd say lean mix did the damage...

[the crafty weasel]

a foreign object would likely cause more damage to the intake side and top of the piston... seeing as how you posted a pic of the exhaust side i'm assuming that is where the worst of the scoring is, so i'd say lean mix did the damage...

 

Thinking about it you may well be right, and judging by the state of the kit there when I started it wouldn't be surprising. Nothing worse than starting a new job and inheriting badly maintained machinery. Didn't happen on my watch, I promise:001_tt2:

 

I'll look into the price of a new piston when I get back in January.

[geoff]

I'd sort that soonest,looks liable to fail.

[Sideleaner]

Thinking about it you may well be right, and judging by the state of the kit there when I started it wouldn't be surprising. Nothing worse than starting a new job and inheriting badly maintained machinery. Didn't happen on my watch, I promise:001_tt2:

 

I'll look into the price of a new piston when I get back in January.

 

A wise decision

 

Pascal

[Catweazle]

It looks as if the piston has overheated by the exhaust port, causing the alloy to smear over the piston ring groove and lock the ring in the slot. The blow past the locked ring just makes things worse. Pistons lose a lot of heat into the barrel, less barrel ( because of the port ) means less heat transferred. Lean mixture is a common cause, caused by a leak in the intake side, holed filter, failed crank seals, too much oil in the mixture or a mismatched exhaust.