Stihl 039 scored cylinder & piston interchangeable with 036?

[ajc4]

I scored the cylinder & piston in my 039 this weekend. Any ideas what might have caused it? The gas was 50:1 AMS oil. The carb was set to the rich setting on the high side as recomended in the manual, and the plug was black, so I know it wasnt running lean. I was cutting a big dead cherry tree -- running it pretty hard. I suspect that I kept it wide open in the log too long and overheated it. Is this possible? I have run it like that before many times with no problem. ---

I can find many used and aftermarket 036 cylinder & piston kits on the internet. I think the 036 is a similar displacement as the 039. Will an 036 cylinder & piston fit on my 039. Will it work with the 039 carb?

 

[Diesel JD]

I heard that there were problems with this saw because the piston is too big for teh jug....I was advised to buy a 310 or and MS361 instead, but as you can see, I ignored them and bought the 390. Hope it isn't true.... and I'm sure someone here will be able to tell you about the intercahnge of pistons..... if not you might be able to find a jug and piston kit at Baileys. Good luck

 

[ajc4]

It is (was) a good saw.

DieselJD,
I think you'll be happy with your saw. I bought this saw on ebay. It was in nice shape have used it for 3 years, at about 25 chord per year. Perhaps this was a pre-existing condition on mime because I bought it used. I see a lot of people on here prefer the "pro" stihl saws, but for firewood it sure has a lot of power for the price. Never had a problem with mine -- untill this week.

 

[Lakeside53]

I
I can find many used and aftermarket 036 cylinder & piston kits on the internet. I think the 036 is a similar displacement as the 039. Will an 036 cylinder & piston fit on my 039. Will it work with the 039 carb?

No, the 036 is an entirely different engine...

 

[Diesel JD]

This is what I thought, seems like teh piston and jug would have to be from another 39. Thanks for teh info about the saw, I like it a lot so far, but yours may have been abused by a previous owner. Heck I think we all abuse them to one degree or another, but both my other Stihls ahve always had the right oil mix in them and still turn freely and are in gret shape compression wise even after all the abuse, it's the fuel system that could use some help. Good luck with yours,
J.D.

 

[fishhuntcutwood]

This is what I thought, seems like teh piston and jug would have to be from another 39.

The 029/290, 310 (not 031!) and the 039/390 jugs are all interchangeable. They're all the same saw, but with a different bore. You can find 029 kits on ebay quite often, and I did see a kit for an 039 the other day, so they are out there.

Andy, how you been?

Jeff

 

[Diesel JD]

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...

 

[Simonizer]

Was the piston scored on the intake or exhaust side?

 

[ajc4]

The piston is scored on the exhaust side. -- I am told this is an indication of a lean condition, but I am sure the carburator was set correctly. I was using the saw wide open in a tough log and ran it out of gas. After I filled it back up, it wasnt running quite the same - wouldnt idle well, and after it got hot it would die. I dont usually run the saw out of gas. I usually noitce it sputter, shut it off and refill. This time I wasnt paying attention to it and did actually run the saw completely out of gas untill it stalled (wide open the whole time).

I ran about another tank of gas through it, babying it along and trying to figure out what was wrong before I check the piston & realized the problem.

I guess that when I was running hard and ran out of gas that the carb wasnt getting quite enough gas for a bit (sucking fumes so-to-speak) which caused a temporary lean condition, which caused the damage. Sound possible? I just dont know.

The rubber intake to the carb is good. I see no cracks in the fuel line. The saw will run untill it gets hot. -- I did run it wide open for a bit before I figured out the problem, checked the plug. It was black. No indication of a lean carb setting.

 

[TimberPig]

I guess that when I was running hard and ran out of gas that the carb wasnt getting quite enough gas for a bit (sucking fumes so-to-speak) which caused a temporary lean condition, which caused the damage. Sound possible? I just dont know.

This is exactly what happened. You were running it hard, it leaned out and squeeked the piston as a result.

 

[ajc4]

Thanks, TimberPig.
Sure wish I didnt have to learn the hard way that running out of gas could cause so much trouble. Bummer.

 

[TimberPig]

In a 2 stroke engine, particularly a premixed one like a chainsaw where the lubrication is delivered by the air/fuel/oil charge, it is never a good idea to run completely out of fuel. When you run out of fuel, particularly with lean fuel/oil ratios (50:1 is not a pretty lean mixture to begin with), you lose your lubrication. When you are working it hard like you were, and don't have enough lubrication, plus the higher temperatures created by lean air fuel when you are running out of gas, often equals a piston seizure.

Also, if you have limiter caps on the carb, and it was adjusted to the stop with them on, it may have still been slightly lean. Proper adjustment with limiter caps often means removing them, making the adjustmens and reinstalling the caps, as they prevent the adjustment from changing. Set from the factory, saw carbs are lean and have little adjustment before hitting the caps. The idea of the caps is to prevent saw users from running their saws too rich and increasing emissions, but in reality it just means they have to be removed to make the proper adjustment. The hope is that only saw techs will be able to adjust the carbs, and most will run lean to meet the EPA's idea of a clean running saw being a well running saw. This idea means most saws are fairly lean to begin with if not checked and adjusted. Unfortuantely it makes them vulnerable to burning down.

 

[Diesel JD]

I didn't know that it was bad to run a chainsaw out of gas, I've done it to every one of mine including the new one since it guzzles fuel faster than all the others. I thought this was only a problem in 2-strokes with multiple carbs like a V4 or V6 outboard. When you run out of fuel you run out of oil, but once you run out of fuel you stop, and you don't start again until you have more fuel and oil, right? What am I missing...? I'm not trying to be combative, I was just trying tolearn, as this is standard practice by some folks with O/B engines with only one carb. It avoids varnishing the carb...to intentionally run it dry...but maybe water cooled are different than air cooled that way?

 

[ajc4]

In a 2 stroke engine, particularly a premixed one like a chainsaw where the lubrication is delivered by the air/fuel/oil charge, it is never a good idea to run completely out of fuel. When you run out of fuel, particularly with lean fuel/oil ratios (50:1 is not a pretty lean mixture to begin with), you lose your lubrication. When you are working it hard like you were, and don't have enough lubrication, plus the higher temperatures created by lean air fuel when you are running out of gas, often equals a piston seizure.

Also, if you have limiter caps on the carb, and it was adjusted to the stop with them on, it may have still been slightly lean. Proper adjustment with limiter caps often means removing them, making the adjustmens and reinstalling the caps, as they prevent the adjustment from changing. Set from the factory, saw carbs are lean and have little adjustment before hitting the caps. The idea of the caps is to prevent saw users from running their saws too rich and increasing emissions, but in reality it just means they have to be removed to make the proper adjustment. The hope is that only saw techs will be able to adjust the carbs, and most will run lean to meet the EPA's idea of a clean running saw being a well running saw. This idea means most saws are fairly lean to begin with if not checked and adjusted. Unfortuantely it makes them vulnerable to burning down.

I'll look into moving the limiter caps. What you say makes a lot of sense. My dad's old saws ran 32:1, and smoked like hell, but they lasted under comparable usage for over 20 years. The new stuff seems to start easier, rev higher, has more power per cc, but just doesnt last.

Do you have any advice about saving the cylinder? The scratches arent very deep, but deep enough to be of concern -- and dont seem to go through the chrome liner (or whatever matreial it is). I think I will try to clean it up with a soft scouring pad & maybe a few strokes with some emry paper and throw in a new piston. Keep my fingers crossed and remeber to keep gas in it from now on!

 

[TonyM]

It is better to stop as soon as you detect a lean running condition due to the pick up filter not being completely submerged in fuel. You can tell when the tank is getting low, and when you do, stop and add fuel then. The saw will be more hesitant accelerate when giving it throttle, and it will loose power in the cut.

 

[TimberPig]

If the plating isn't scored deep enough to catch a fingernail, then a light hone with a ball hone will fix it up after removing the aluminum deposits with muriatic acid. Just wipe the acid on, let it work, wash off with water, then hone and oil it. Make sure to keep it off the outside of the cylinder, because it will eat the aluminum there just like the aluminum piston streaks stuck on the plating. If you are lucky, the cylinder can be saved and you will only need a new piston and rings, and base gasket. I would check to make sure that it doesn't have an air leak anywhere either, although I don't think this is the case here, just to ensure that your fresh top end doesn't get burnt up right away.

 

[ajc4]

I didn't know that it was bad to run a chainsaw out of gas, I've done it to every one of mine including the new one since it guzzles fuel faster than all the others. I thought this was only a problem in 2-strokes with multiple carbs like a V4 or V6 outboard. When you run out of fuel you run out of oil, but once you run out of fuel you stop, and you don't start again until you have more fuel and oil, right? What am I missing...? I'm not trying to be combative, I was just trying tolearn, as this is standard practice by some folks with O/B engines with only one carb. It avoids varnishing the carb...to intentionally run it dry...but maybe water cooled are different than air cooled that way?

On my saw, if I listen carfully, I usually notice subtle hints that it is getting low on gas. For example as I lift it from cutting one log to the next it might hesitate as the fuel sloshes around and looses contact with the suction hose. This particular time I was right in the middle of a big cut, going full blast, working hard with a hot engine. Basically the worst-case scenario. As timberpig points out, these new saws under tough EPA regulations are running as lean as they can. What he says makes sense. I am certain that my saw ran perfectly before that fuel run-out, and ran very badly afterward. Like night and day. No other explanation makes sense.

To be on the safe side -- my advice would be to try to not run that shiney new saw out of gas. Taking a break to gas up should be good for both you and your saw. If it sputters or anyting STOP, fill up. I think I will switch to 32:1 from now on too.

BTW: A new piston from my local shop is $88. A new cylinder+piston set is $210. A new 390 is upwards of $400 depending on which bar (if any). So to fix my 5 yr old saw the "right way" is half the cost of a new one. -- Thats why I'm thinking of trying to clean up the cylinder a bit and go with just a new piston.

 

[TimberPig]

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.

 

[fishhuntcutwood]

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...

Off the top of my head, the bores are 46, 47 or 48 and 49 mm for the 029, 310 and 039 respectively. The three milimeters between the 029 and the 039 is quite a bit, and I don't reckon the 029 has cylinder walls that thick. I also think it'd cause problems with the ports if they were all the same jug bored to spec. I've not seen any two of these jugs side by side, but I'd have to say that they are three completely separate castings, and not just one bored out to different diameters and that boring an 029 jug out to 310 or 039 isn't feasable. I can't see boring anything 1 or 3 mm over.

Jeff

 

[pinus]

Off the top of my head, the bores are 46, 47 or 48 and 49 mm for the 029, 310 and 039 respectively. The three milimeters between the 029 and the 039 is quite a bit, and I don't reckon the 029 has cylinder walls that thick. I also think it'd cause problems with the ports if they were all the same jug bored to spec. I've not seen any two of these jugs side by side, but I'd have to say that they are three completely separate castings, and not just one bored out to different diameters and that boring an 029 jug out to 310 or 039 isn't feasable. I can't see boring anything 1 or 3 mm over.

Jeff

I think that the jugs of 290-390 are the same castings bored only to different diameters. If to look for example Stihls 270 and 280, 44 and 46 mm correspondingly, then from DLG tests is obvious that 270 has powerband shifted to higher rpm-s than 280, which refers to smaller intake and exhaust port areas relative the cylinder displacement for 280. If to bore open port design to the larger diameter, then intake ports are reduced somewhat, etc.
v.