Time to get familiar with Dolkitas... picked up a 6401 today.

Also (and I realize I'm reaching a bit far here), I wonder whether an almost-new saw would seize more quickly when something goes wrong because the clearances are tighter?

 

Still dunno. Anything from here on out that I would have to say is pure speculation, so I'm going to sit back and let the experts chime in. Good luck.

 

I can't say I've got much more than that myself.

 

Another little shred of evidence that may support the straight-gas theory: while I did wipe the cylinder bore clean with a paper towel, I did not do any detailed swabbing of the open transfers. And yet, they are bone dry, free of oil even down in the corners and crevices...

 

I wonder if the previous owner was smart/dumb enough to dump some oil in the cylinder to try to free it up?

 

Doubtful. Everything on it was buttoned up like it came from the factory -- nothing out of place, no marred fasteners. Besides, it wasn't that much oil; just enough to be pushed around by the crank counterweights as they swept through, i.e. a small fraction of a teaspoon.

If I'm interpreting the SN correctly, the saw was built in March of 2008. My guess is that it broke not long after that, and has been sitting accumulating dirt and cobwebs ever since.

 

I think I'd replace the piston/ring, and roll with it... They are very good saws in their 65cc form...
$49.00 and you're back in business...

 

I'm about 90% sure it ingested something too... It came up the one intake side transfer, and caused it's damage, then out the exhaust it went... I'd check inside the muffler.

 

I had the same thought about the exhaust-side transfer being due to pressure from the intake-side buildup. But as to it's eating something, the filters were clean, intact and solidly installed, and I don't see any missing components. Still no debris of any kind, either. Nothing in the combustion chamber, crankcase or muffler.

I hear you re:surfaces being cooled by the incoming fuel, but at the same time it's the intake side that would be washed clean of oil first.

 

Does anyone have a trick for testing whether gas has 2-stroke oil in it? I still have that jelly jar full of it, and it sure looks like ordinary gasoline.

 

But the whole side is washed evenly normally...
This area of damage looks very localized...
Not sure what it could have been...

 

http://www.2-stroketest.com/kits.html

If you want to be less than scientific, you can dip your finger in the "mix" and let it air dry. If oil is present you'll feel the residue when you rub your fingers together after the gas evaporates.

Or - run what's left over through a small 4 stroke engine an watch/smell the exhaust for signs of oil.

 

Maybe someone sprayed starting fluid in it?? ... Doesn't look like a straight gassed piston to me.


I'd contact weedeaterman and see which 79cc kit he reccomends and how long to get it if backordered.

 

Sorry guys, I'm at work and won't be able to follow up in depth until tomorrow. Carry on with the speculation, though.

 

Oh, and fwiw I don't remember noticing any oily residue inside the muffler, but it looks like the saw had been sitting a long time so that may not be meaningful.

 

Well, it seems that confirmation bias led me astray. This morning I put a couple of teaspoons of the fuel onto the clean bottom of a tomato can, and used a low heat gun setting to evaporate the fuel. It did leave behind a light oily residue, dealing a nasty blow to my straight-gassing theory.

Following up on Hedgerow's observation that the worst of the transfer was localized rather than spread across the whole intake port area, I figured I'd look for nearby problems. Could there have been a leak on one side of the intake boot? No, the boot was in excellent shape, soft and supple. Could it have been adjusted too lean? Nope, the high-speed limiter is intact and set near the rich end of its range. What else is near there? Well, the impulse line comes in on the damaged side... holy, what the...!?



That isn't even all of the damage. The impulse line is riddled with cracks, both longitudinal and transverse. It's practically falling apart.

Now I'm mostly wondering, how the heck does this lousy impulse hose end up on this particular saw?

 

Just to be absolutely sure, I would do the same gas in a soup can thing with some known unmixed fuel.