Stuck Piston Ring - Husky 435

[waldonh]

I've enjoyed looking over post for the past month. I'm hoping some of you can help me.

I'm using my saw to cut firewood. My Husky 435 is one year old and has had maybe 3-4 gallons of gas run through it. I brought it into a local dealer because it was almost impossible to start after the saw was shut off when hot.

The condensed version of the story is that a stuck piston ring was discovered which damaged the cylinder and piston. Husqvarna won't honor the warranty because they say I ran straight gas (which I did not). Because of a couple different details the dealer absorbed the labor costs and I paid for the new cylinder assembly.

Now I'm concerned that whatever caused the piston to become stuck the first time, might happen again.

I have a couple of questions...

1. Is it possible the ring was never seated correctly to start with?

2. Could this be a result of the 10% ethanol gas sold locally? I've bought the gas at a quality station and used the 87 octane grade. I've used the husqvarna low smoke oil. I've read many posts about using a higher octane grade and possible even adding a marine stabilizer to offset the ethanol.

3. Do I need to break the saw in again, like when it was new because of the new cylinder assembly (the manual says something to the effect of only running it for 1/2 hour at a time for the first 10 hours)?

Thanks for your thoughts!

 

[rmh3481]

A stuck ring generally happens from heat. As the piston temperature continues to rise, the aluminum becomes softer and softer until its pulled up over the ring. This of course sticks the ring in the groove of the piston, and then the ring cannot touch the cylinder wall to hold the compression or pressure of the burning fuel.

Make sure you run fresh fuel, under 30 days old. Use Hi Test gas from one of the major stations because it generally does not have the ethanol in it. In addition, run your fuel mix at 32:1 rather than 50:1. I think a little extra oil is in your best interest especially with a new engine.

Phase separation occurs because ethanol will hold water. Gasoline was developed not to hold water. Of course water wont mix with oil either. When the amount of water in your fuel reaches a certain level by volume, the lubricating oil is forced out of the fuel mix either entirely, or to the point where there is not enough to lubricate the cylinder. Hence the heat from friction begins to build and the piston distorts.

Always keep your gas tank tightly capped. There is alot of moisture in the air, and you see this on your yard at night in the form of dew. This moisture will collect in your gas can unless its covered...

Best wishes,
Bob

 

[TraditionalTool]

A stuck ring generally happens from heat. As the piston temperature continues to rise, the aluminum becomes softer and softer until its pulled up over the ring. This of course sticks the ring in the groove of the piston, and then the ring cannot touch the cylinder wall to hold the compression or pressure of the burning fuel.

This is exactly what happened to a Husky 350 I bought last week. I just pulled the piston off, and I thought I could get the ring out by using a file to remove the aluminum that is scorched across the ring. It seems the heat deformed the slot and that the slot is not level anymore, and it won't allow the ring to lift out on that side... I ordered a new piston anyway...

In theory, you can have some tolerance with the piston as long as the ring is seated ok, and can float in the slot. Isn't that correct?

 

[mountainlake]

Saws nowdays come set LEAN, pull the caps and set richer. Ethonal makes it worse and it doesn't store well, add a little Stabil or Seafoam when your going to store it for a while. Steve

 

[mountainlake]

This is a Husky that melted down for all of you that think only Dolmar melts down. I know several people with Stihl's that have lean siezed also. These carbs need to get adjusted right, if the dealer won't then we'll have too. Maybe the 5100 comes set a little leaner for the EPA credit thing with Dolmar thinking that the 5100 won't be in long hard cuts as much like the 7900. I just got done putting a new P@C in my friends 7900 the melted but was more likely from sitting too long with bad gas. They all melt if set to lean with Stihl and Husky having more leeway on their saws as they have more 4 stroke engines in their lineup to balance the EPA credits. Steve

 

[blsnelling]

First of all, it's highly unlikely that the ring stuck first and then caused damage to the piston and cylinder. It would be the other way around. The piston gets too hot and expands, with then gets tight in the cylinder bore. As this continues, aluminum actually melts from the piston and smears on the cylinder wall. The aluminum also smears across the rings and sticks them in the groove. There are three main causes of this.

1. An air leak in the engine that causes it to run too lean.
2. The carburetor not properly adjusted, causing the saw to run too lean.
3. Too little or no oil in the gasoline.

I don't know if your saw has a catalytic muffler or not, but this just further compounds the problems when they do.

Yes, it will have to break in again. It's the topend that has to break in.

If they didn't find the source of the first seizure, it's likely to happen again.

 

[waldonh]

I've learned quite a bit reading everyone's responses. I also learned quite a bit reading the thread on the dolmar saw.

Let me first say I had no idea that 2 cycle engines were so sensitive. I've got to learn how to "hear" my saw and have also got to learn about tuning my little saw.

I tend to think that my saw may have been tuned "on the edge" or lean (it has always been a bear to start when warm -- is that an indication of a lean tuning?). I purchased it at a box store. That combined with 2-3 month old gas (learned a ton about why ethanol means one has to be more particular about gas storage) and a first time saw owner running a chain that probably wasn't as sharp as it should have been may have lead to my original problem.

I like the suggestions presented and will take advantage of them. When told to get hi-test gas, I assume you mean not just the 89 ocatane, but the best the station sells. I also like the idea of making the oil mixture a bit more rich. Am I correct in assuming this will provide a bit more safeguard?

On the topic of storage, when I bought the saw last year, I got a one gallon tank that has a spill proof spout (turns off when fill the tank and the tank is full). I've been storing the tank with the spout facing out in my garage. I'm curious how air tight that spout is, I wonder if it's compounding the problem by letting the moist basement air into the storage tank...

Thanks for the responses, hopefully I can keep this saw running for some time to come.

 

[Cliff R]

My 435 wasn't too far off right out of the box. It was ever so slightly lean, but a lot closer than most of the new saws we see these days.

They require a "special" screwdriver to adjust them. I'd open up the "H" speed screw some during break-in, slightly more open than the ideal setting for best power and most rpm's.

Once you get some time on it, lean it up for the best power in the cut.

I've noticed with the 435, that it really loves to rev, and seems to like a lean setting, but looses some mid-range power if you set it up for best high rpm power and a lot of rpm's. I fatten mine up some, so that it pulls best in the cut with some decent load on it, and "four strokes" immediately if the load is removed.....Cliff

 

[waldonh]

Cliff,

I've heard the term "four strokes" a couple of times. Forigve me, but I'm new at this two-cycle stuff. It's obviously making reference to the four stroke motor, but what is meant by it. How does it sound different than the two-cycle sound?

 

[Cliff R]

"Four stroking" has been discussed in depth on this website. Reminds me of hitting a rev-limiter and the engine starts missing and rpms will not increase any further.

As soon as the engine see's load at this point, it smooths out/cleans up in the cut.

I've never to date had any issues with any saw with pistons, rings, or cylinders.

I add a bit more oil to our mix, around 40 to 1 instead of 50 to 1, using only Premium Husqvarna or Stihl oil.

All of our saws, and the saws we work on are finely tuned for best power in the cut and I don't push them for really high rpm's when setting the carburetors "H" speed screw. I like to start a tad rich, then work them in the lean direction to obtain best power in the cut and still have the engine "four stroking" when the load is removed. This has proven to keep the engines in a safe zone, regardless of make, model type of engine (reed valve or piston ported).

With most modern saws that we see here that have piston/ring or cylinder damage, it's due to the "H" speed screw being set too lean. This happens because the factory is trying to please the EPA by limiting the amount of combustion byproducts that exit the exhaust.

Echo saws are the worst of the bunch, at least for setting their saw extremely lean right out of the box. This causes quite a few P/C failures with them, giving them an undeserved bad reputation. As mentioned above, our 435 wasn't off much, and would have been fine right out of the box, although it was lean enough that it was giving up some mid-range power in the cut.

The 435 uses a strato-charged engine, and after working with it for some time now, I've found that I really like this technology. They make a LOT of mid-range power, and still plenty of high rpm power. The power curve is broader than the other Husqvarna saws I own with closed port jugs, and it makes a lot of power for the size of the engine. I suspect we'll see this technology spreading through most of their line-up, as they are also supposed to be much more emission friendly as well......Cliff