Stihl 039 scored cylinder & piston interchangeable with 036?

[NathanA]

Make sure to check the intake rubber pipe for a hole this can cause the saw to lean out when saw get's hot also the compensator line on the carby can alsobrake and cause leaning out

 

[bugfart]

When adjusting a carb, we are advised to use half a tank of fuel so it doesn't run too rich when filled.

However, if you adjust your carb when the tank is full, you create a lean mix toward the end of the tank, shortening the life expectency of the saw.

I say this is why some saws last a long time and others not so long, all else being equal. It would be nice to have a float built into the tank to short the plug when low, but this is not practical. Or is it?

 

[Lakeside53]

So Jeff, if the jugs are all teh same, then do you ahev to have teh jug bored to specs at a machine shop say they all start out as MS290, out further to MS390 or 310? Wouldn't be expensive, but then you'd have to find a piston and ring for it...

Sorry, you can't bore these. They are nikersil coated... If you bore the jug, you'd just be running the rings on aluminum.. Also, if you downsize to an 029, you'd need to change the carb. Cheapstihlparts on ebay has a few good looking used 039 piston cylinder sets.

 

[Lakeside53]

DieselJD
The reason it can lead to a burn down of your top end is because you lose the lubrication when you run a pre mixed 2 stroke engine out of fuel. If you aren't pulling fuel in, you aren't pulling oil in. If the air/fuel mix is lean already, then there is already more heat being created, then you turn up the heat more when the fuel runs out and makes the saw run even more lean just before it dies, and then you take away its lube. If it is pulling hard as in this case, it can make the top end seize.
As to running out of fuel, if you aren't at max revs under a good load, you often get lucky and it dies without causing damage. We've all done it, but it is not a good practice. Sometime you get unlucky and it bites you by your top end seizing.

On many saws as they run out of gas they lean out and speed up significantly (like turning in the H screw). I hear guys up a tree blocking big fir milking the last drop out of their 44s, and they (the saws) are just screaming. Makes me cringe... and I know it's only a matter of time before I have to tell them the sad tale of how much it's going to cost to fix it. I'm guessing that the 044 goes from about 12000 to 16,000+ during the process, and thats really hard on the bores, pistons and bearings. I'm rebuilding an 088 where the "kid" was cutting out a big cedar stump and screaming the saw until it ran out of gas. Never did want to pull over after that. The rod bearing seized, threw off some chunks and took out the piston and cylinder. About $700 (list) in parts... Another thread stated today about "running out of gas"... probably a better place to continue this discussion.

 

[Diesel JD]

How about honing the cylinder, new piston and a new ring? Honing using a bottlebrush just as is done on larger engines.

 

[ajc4]

How about honing the cylinder, new piston and a new ring? Honing using a bottlebrush just as is done on larger engines.

I havent located a used 039 cylinder yet -- so thats what I am going to do. It will take me some time to get parts and get it back together. I'll post back what the results are when I'm finished. After some work with a power drill driven scouring pad thingy (soft enough to not affect the chrome liner), and some engine degreaseer to remove the melted piston aluminim from the cylinder walls and a light rubbing with some emry paper (I dont have a honing tool, and am not sure where to get one), it looks OK. I can feel some fine scratches still in the piston with the sensitive part of my fingertips, and you can see them with a good light. I am sure the saw will never pull 150 psi compression again, but I''m hoping it will be over 130 or so when I get done.

Many here have suggested using miratic acid on it. --- Its just not worth saving $120 on a cylinder to me to risk melting my hand and inhaling wierd fumes from that stuff.

 

[TimberPig]

I

Many here have suggested using miratic acid on it. --- Its just not worth saving $120 on a cylinder to me to risk melting my hand and inhaling wierd fumes from that stuff.

If you wear rubber gloves and do it in a well ventilated area, it is a perfectly safe procedure as long as you are sensible about it. It is the standard procedure to remove melted piston from a cylinder to save it.

 

[Lakeside53]

If you wear rubber gloves and do it in a well ventilated area, it is a perfectly safe procedure as long as you are sensible about it. It is the standard procedure to remove melted piston from a cylinder to save it.

and to add to this... you'll cause a lot less damage if you do use the acid... If you want to get a real nice cross hatch, go down to your local auto parts store and buy one of the honing tools that looks like a bottle brush with big carbide blobs on the tips. These work VERY well on chainsaw bores... after the acid. BTW, on the "acid scale", this is about 20% Hyrochloric acid and isn't particualarly bad. It's far less corrosive than the acid in your battery.

 

[ajc4]

Just a follow-up on this:

I put a new piston & rings in friday, ran maybe 5 tanks of gas through it bucking some big logs. Seems to be breacking in normally & working fine. The few fine scratches near the exhaust port dont seem to be a problem. Its pulling a bit over 150 psi compression. Thanks for all the advice everyone here gave me.

 

[TimberPig]

Glad to hear its back together and working good. Plus, you learned a few things about saws in the process, for a much smaller investment than it could have been if you had pitched the saw or replaced everything with new.