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

...and, nailed it. It was straight-gassed after all, but the scoring was confined to the intake side of the cylinder where I couldn't see it until I dropped the piston out of the way. Time to go shopping.

 

Looks green to me! I looked on their website and everything there is green. http://www.makitatools.com

I have a Makita cordless drill... It's white, but the charger is normal Makita green.

 

It is a slightly greenish, tealey blue. If it looks like kelly or forest green, you may need to adjust your monitor's color settings a bit.

 

OK, I'll meet you at teal.

 

Thanks for the tips. I am currently cleaning it up so it can be disassembled without risk of dropping junk into the case. I should have the cylinder off before long, more pics to come...

 

BTW, I've only worked on a couple of saws with ruined top ends, so I am not even all that confident in my ability to distinguish transfer from other sorts of scoring.

 

I'd try to clean up that cylinder for now. Weedeaterman.com is cheaper for the same kit. I'd go oem 7900 for not much more.

 

So far the only source I've seen for the OEM 7900 kit is one eBay seller, and it's more than twice the price of the aftermarket ($250 vs. $114). But, weedeaterman has the aftermarkets on backorder, and if there's a saw that would be worth the investment in the OEM it's this one. Aside from speckled oil stains on the plastic handle / gas tank and a tiny patch of scratched magnesium on the bottom, it's virginal. This is all a bit premature, though; I need to make sure there isn't a crank or rod problem first.

 

Here you go. No obvious bearing failures or debris in the case.

Here's what was in the gas tank:



Intake:



Exhaust:



Interesting case, eh?

 

Looks like it swallowed something? Maybe a throttle plate screw or a piece of spring

 

Haven't found anything yet. Contrary to MM's prediction, there's a lot of aluminum transfer on the intake side, and just a little next to the exhaust. Not much in the way of scratches.

 

Any bits and pieces / shavings down in the crankcase? Did you clean that piston up any? It looks VERY clean. I'm far from an expert on this with 2 stroke engines, but something went very wrong very quick...almost like a foreign object was in there...but I'd expect to see some scratching too if it wedged in there. Dunno.

 

I'd say you could put a piston in it and be good. There's plenty of the 6400 cylinders and pistons out there cheap also. People swap them to BB and 7900 kits all the time.

http://www.edgeandengine.com/dolmar or http://www.fastcutting.com/ for dolmar parts at a good price and very quick shipping.

 

I wiped off the oil with a paper towel so I could see the surfaces better, but that's it. I haven't found a single bit of debris in the engine, and I can't see any scoring to speak of inside the cylinder either.

I've just looked at several photographic piston diagnosis articles / charts, and the best matches for aluminum transfer on the intake side and/or both intake and exhaust sides all indicate lack of lubrication. They also say such failures are quite rare.

 

Thanks for those sources. I did find one place selling the OEM 7900 cylinder kit for $211 shipped, which is also tempting.

 

If you had oil to wipe off, then there would be at leas some lubrication present, no? What about the wrist pin and crank bearings? They oily?

 

Yeah, P&C were a bit oily, which is very inconvenient. There's a bit of oil pooled in the crankcase, so it's possible that the surfaces were drier (of oil) to begin with, and got relubricated as I turned the saw this way and that.

Big-end rod bearing feels great. Crank bearings feel great. Wrist pin bearing was a bit looser than I expected, but looks absolutely normal. There was some oil on the wrist pin too, I think.

I'm not feeling especially confident of the straight-gassing theory, it's just the best I have so far.