Stihl 041 Farm boss smashed second piston...

[EngineNoO9]

Ok sorry to post about this saw again but figured I needed to give this one it's own thread. I'm at a loss and I'm probably giving up on this saw after this one unless someone can give me a good idea why this happened for the second time. First piston seized and I assumed it was probably because of crap in the cylinder since it had sat so long. So it sat for a very long time until I just bought a new cylinder and piston. Installed it and it fired quickly. Ran for maybe 30 seconds and then stopped. I couldn't pull the handle and I'm thinking crap... It happened again. Well, I looked it over and I could still spin it but it kept stopping at one part of the stroke. Ended up pulling the bar oil filler and it let me spin it again. Yay. Well. Couldn't get it started still so I looked things over and saw that my spark plug had a bunch of metal on it. Odd. Thought probably from when the last piston seized but this one was still spinning so I figured I'd be good. Well. Out of precaution I broke it down to make sure the piston was clean and there were no flakes in it that'd potentially destroy another cylinder and piston. Get the cylinder off and this is what I see...



That doesn't look good. Take my time trying to get it out to make sure i don't damage the cylinder if possible. It got stuck once but I think I managed to save the cylinder maybe....

So here's a closer look






So um. Yeah. Not sure how that happened. When it was still attached I looked at the stroke and couldn't figure how the heck it smashed that part. Thoughts? As mentioned I can't see dumping more money into this (have a sprocket and bar on the way for it too. Though the bar should easily be returned) unless I can figure out it what's wrong (within reason). It's looking like it's most likely going to be a parts saw though....

 

[Kenskip1]

Was this a new piston? The first thing that comes to mind is if the piston was installed backwards.Second thought that one of the wrist pin keepers let go. Where is the lower ring?Ken

http://www.hlsproparts.com/Stihl-041-cylinder-and-piston-assembly-44mm-p/cp30041.htm

 

[EngineNoO9]

New to me piston and cylinder. Maybe I installed it backwards... Which way should it go? I'm confused cause the first one I never touched... Maybe that was a fluke and this one is my dumb ass self

 

[EngineNoO9]

Arrow was pointing up. Ring gap was on bottom. So that should be right. Crank spoke but there's metal in it for assure from the piston. When the other seized on me I don't remember it breaking like this. I think the ring just broke on it and caught the exhaust port

 

[Kenskip1]

Well this is a lesson learned. The arrow points toward the way the mix is flowing. Out! The arrow always points towards the exhaust side of the piston.Do NOT feel bad. This has happened to a lot of others.You learned a valuable lesson.Unfortunately this little foe~pau may cost a few $$$ Ken

 

[EngineNoO9]

Hmm as I look at it I see the ring caught the cylinder. Not really sure what happened to the back of the piston though. That had me scratching my head a little. If I I had it correct it wouldn't have been able to. *sigh*. The cylinder is toast. Crank needs to be cleaned of metal. I'll set it aside to get a new cylinder at some point when I'm over me being an idiot.

 

[ericm979]

The piston is set up to run the ring gaps in the safest part of the cylinder. If you reversed the piston they'd be somewhere else making it more likely to snag the ring ends on a port. The arrow usually points to the exhaust but check it in the manual to be sure. Ring gap could have been too small, so when the ring expands as it heats up it has no where to go and bulges out into a port. What does the cylinder look like?

Even with OEM parts I sometimes get a part that doesn't fit right. With AM it'll happen more often. Check everything before assembly.

 

[EngineNoO9]

Cylinder is gouged and is toast. I got thrown off by the comments with the arrow pointing to the exhaust cause the exhaust port is on top the same as the carb. But the ring gaps definitely caught because it was flipped upside down. Didn't break somehow though. Smashed the piston up. Lesson learned. I won't toss it. Clean and full rebuild (with another used cylinder and piston) as I'll have to crack the crank open to get the metal out of it.

 

[EngineNoO9]

Well this is a lesson learned. The arrow points toward the way the mix is flowing. Out! The arrow always points towards the exhaust side of the piston.Do NOT feel bad. This has happened to a lot of others.You learned a valuable lesson.Unfortunately this little foe~pau may cost a few $$$ Ken

So riddle me this... Exhaust and carb are mounted on the same side of the cylinder for this saw.... Looking at it the arrow definitely needed to aim down in this case... Am I missing something? And any thoughts to clean the crank short of splitting it?

 

[ericm979]

You can try flushing the cases out with premix. But if there's any metal that goes in the bearings that'll kill them quick.

Try to find a workshop manual. See the "beg for manuals" sticky thread. The arrow points toward the exhaust port on most engines but somehting this old who knows? Best to check what Stihl says.

Another way to tell in piston port engines is that the intake side of the piston often has a shorter skirt than the exhaust side. But that's not always true either. A third way to tell is to see where the pins in the ring grooves will place the ring ends. Like I said above that's usually in a safe place (i.e. the ring ends won't go across any ports). But I have seen engines where the ring ends did cross ports, though they were small transfer ports. Some engines have so many ports that there's no clear cylinder wall for the ring ends.

 

[EngineNoO9]

I'll probably just see about splitting the case open. It sucks but I need to make sure metal is gone.

 

[Wood Doctor]

I'll probably just see about splitting the case open. It sucks but I need to make sure metal is gone.

I had the same thing happen with an 066 engine this past winter. It ate up three pistons and rings exactly the same way before I gave up. The skirts crashed against the case. My solution was an all new case assembly and I rebuilt the saw around it, but to my knowledge that assembly does not exist for an old 041. Maybe it does, but it will likely cost more than the saw is worth.

 

[EngineNoO9]

I had the same thing happen with an 066 engine this past winter. It ate up three pistons and rings exactly the same way before I gave up. The skirts crashed against the case. My solution was an all new case assembly and I rebuilt the saw around it, but to my knowledge that assembly does not exist for an old 041. Maybe it does, but it will likely cost more than the saw is worth.

Interesting. I don't think that's what happened here as the ring gap was right on the edge of a port of the xylinder... But you're making me worried! You think there's any kind of check? Best I can figure is look at the stroke and see if there looks like any interference

 

[ericm979]

You should always run the engine through a couple rotations by hand after assembling it (plug out).

But you can check the piston skirt clearance vs the crank and cases before assembling the motor by putting the piston on the rod and rotating the crank through BDC while holding the piston where the cylinder would put it. This test is not exact because you might not hold the piston exactly right but it'll catch gross mismatches.

All manufacturing has tolerances. For example the level of the crankcase where it's machined for the cylinder may vary .2-.5mm. Rod length can vary. So can piston skirt length. (and of course there can be running changes that happened in that models' life). If you get all the tolerances going the wrong way- low cases, short rod, long skirt- the skirt and crank could interfere. Some manufacturers will spec things so that no matter how the tolerances fall nothing will break. But that can leave a lot of performance on the table. Others (German two stroke motorcycles in my experience) will make the "normal" fit right but that means that you have to check the tolerances when you assemble with new parts.

So did you end up with broken rings? The small dings in the piston crown and the gouge on the skirt look more like broken rings than piston skirt chunks.

 

[Wood Doctor]

I actually considered grinding about 0.008" off the bottom of a piston skirt and trying again. However, the piston on the second attempt chipped particles off the case. I figured the bearings and seals were likely almost shot as well. So, I threw in the towel. The new engine assembly worked perfectly with all my remaining parts, and the rebuilt saw is a keeper, sans serial number of course.

 

[EngineNoO9]

The ring stayed together somehow (Bottom ring broke on assembly so I only ran the top one. My original piston was an older one that had only 1 ring as well. The saw ran for about 30 seconds but I guess as it warmed up and the throttle speed increased that was all she wrote.

 

[EngineNoO9]

Haven't messed with it until I looked at it today. There's a gouge in what almost looks like Teflon on the left side of the case. When I look at gaskets online I'm not seeing what the heck this is. So... Is the crank toast? If it can be rebuilt I'll hang on to it till I split the case and replace all gaskets.

 

[Wood Doctor]

Haven't messed with it until I looked at it today. There's a gouge in what almost looks like Teflon on the left side of the case. When I look at gaskets online I'm not seeing what the heck this is. So... Is the crank toast? If it can be rebuilt I'll hang on to it till I split the case and replace all gaskets.

View attachment 646439

That's similar to the case I replaced. Mine was just chipped worse on the edges where the piston skirt rammed into it near BDC (bottom dead center). Again, mine was an 066, but the symptoms are similar and the results are identical.

 

[EngineNoO9]

Interesting. I've toyed with the idea of buying a crank of of eBay and a new cylinder. Will run me like $80'ish but I have all of the other parts to put it together. Still way cheaper than starting with something else. Feels a little silly though as I'll be replacing almost the entire saw though.

 

[JonCraig]

Any chance it was a 041 regular piston and an 041 Super cylinder? Wondering if the piston rocked in the cylinder?