Killed the MS880 while milling

[Kicker_92]

Got the bar pinched in the middle of a slab and must've gotted a bit too hot, and it died. Trying to start it afterward revealed very little compression. :censored:

It melted off a corner of the piston. This also galled up the cylinder head, which might be salvagable with some honing, but the piston is toast.I tried to sand off some of the slag, but the ring grooves are soo tight that the rings are stuck inside.

I'm thinking the mixture must've been a bit lean, the plug was brown, but a very light shade of brown. It'd been running really nice up until then too, but looks like our milling might be on hold for a bit.

Any suggestions? :help:

 

[stihlboy]

sounds like you are in the market for another saw......

p&c is about $350 plus install....

 

[LoggN]

Thats harsh, bit to lean looks to be a factor. Maybe you know but never run the saw dry out of fuel, I hear the quality of our pump gas is garbage! Kinda like this ultra low sulpher diesel they pump into us to ruin our older diesel trucks. Just a thought.

 

[DRB]

So sad

I don't think the cylinder can be saved?

Hope you find a reasonable way to get fixed up a new 880 is not cheap.

 

[chuckwood]

looks exactly like a Husky 350 I'm fixing

So sad

I don't think the cylinder can be saved?
Hope you find a reasonable way to get fixed up a new 880 is not cheap.

The photos of the piston and cylinder look exactly like what I saw when I examined a Husky 350 someone gave me. I read all the threads about restoring cylinders, and started working on mine with muriatic acid, also used oven cleaner. With a bit of work and wet sanding with 400 grit, I removed the smeared on aluminum and got the bore smoothed out. The nikasil coating is so tough that maybe it can withstand a beating like that from a melting piston. I've got a cheap 30 dollar aftermarket piston coming via ebay, and in a week or so, I'll find out if my first rebuild is gonna work. Don't really need the 350, got too many saws as it is, but it was free and I just want the experience of doing it and to see what happens.

It may be that the 880 can be revived with a bit of chemicals and sanding, but with an expensive saw like that, a cheap aftermarket ebay piston may not be a good idea.

 

[BobL]

In analysing the circumstance I'd be asking myself the following
How does a bar get pinched when milling?
What type of wood were you cutting?
How long had it been since the chain was sharpened?
What fuel/lube mix are you running?
How many RPM below max have you got the H screw set at ?
How much pushing was happening?

Fear of this is what leads me to this.

I reckon your cylinder is salvageable.

 

[BlueRider]

In addition to the questions Bob asked I would also want to know what kind of bar oil you are running and if you are using a roller/sprocket nose bar and the lenght of the bar. Of course the piston siezing may have just made it seem like the bar was being pinched.

Your toasted p&c is exactly why I like the older saws over the new ones, specificaly the 075/076 as their design puts the exhaust away from the log where it bounces back into the saw. Bob has addresed this problem with his awsome exhaust pipe mod. I think Bobs clutch cover mod may also lower the running temp due to the decreased heat from a clutch being run clogged full of sawdust. I am a bit on the fence on this mod due to removing the cluth cover also removes a bit of the thermal heat sink that helps cool the saw.

If that is a head temp guage on Bob's saw that is also a great mod and would tell the truth about the effectivness of any future mods. I was just thinking about how to add an on board tack and temp guage as well as extended H and L screws for on the fly tuning.

 

[huskyhank]

Sorry for your troubles.

The rev limit on my 3120 is looking better after seeing this. But I sure wish it had a high speed screw. Keeping the saw on a very slight blubber under load will help prevent this.

 

[Andrew96]

Being an 'engine guy' and having raced..burned, broke many a 2 stroke motorcycle over the years...it's very easy to see what happened to your saw...even without getting a lope out and having a real look. Immediately I see two signs. Signs of detonation (preignition). Yes...very hard to tell on a 2 stroke until it fails if you cannot 'read' a plug properly with todays fuels. However...look at the photo up the cylinder. See the funny burn pattern? Less carbon in the intake side (cooler)..thats good, more on the exhaust side still OK....but look a bit closer...see the specs..the specs where the carbon is missing...the dot like marks. You ran this hot, and fast..but this was preignition that overheated the assembly and overheated (burned) the piston edge. There was more heat in that cylinder than you could cool off due to the ping. Look again at your piston photo. I know you took the photo to show a melted piston onto the rings..but look at the combusion pattern on the top..get your magnifying glass out..that's the key..that's what you should be looking at. On the exhaust side (of course..that's where the heat is), you can see the speckling again. Detonation has broken off the carbon deposits on your piston crown. The problem is..this 'just didn't happen' IMO. Sorry to tell you but look at the missing piston edge. Where did it go? It certainly isn't down the piston skirt. It's been burning off for awhile. Ping by ping. This should have shown up on your spark plug (don't just look at the colour...look for zits on it...speckles of carbon looking stuff..which is actually aluminum). As for a failure mode..well preignition for sure. I don't think getting the saw stuck (still don't know how) had much to do with it..other than some extra heat. This has been on a route to failure for awhile...at least for the last 10 - 20 minutes or so.
I think you'll be able to save that cylinder (if you're careful with the acid). I'd pull the crank and make sure there isn't anything, other metal debris down there. I'd then be checking your ignition timing. If that's fine and hasn't moved..then your fuel has water in it, is of too low an octane for your compression, or location, or (though I don't think so..without looking at your assembly under magnification) you just plane ran it too lean (lean doesn't usually = preignition though). Too much timing, or low octane like water or wrong gas, old gas.
Just my thoughts. I've only seen insides of various engines that look like this oh....say 250 times.....

Just looking at your photos again...did you run the proper amount of oil in your fuel? It's hard to tell from the photo but it looks like you have some galling on the piston pin? That's very hard to do...but could just be dirt from your fingers...or some other mark.
Kind of a lot of blow by for such a low compression engine. Are you sure this didn't have tons of hours on it..coupled with some preignition?
When you get it together....put a lope in your tool box to look at your spark plug (check for acne on the ceramic bit, electrodes).

Here's a new rule for you....If you're ever running an engine and all of a sudden it just decided to run really really great...remember to enjoy it since it's just about to fly apart. After a few failures you'll remember to shut it down pull the plug, get the lope out to read the plug.

 

[huskyhank]

I think Andrew96 has hit the nail on the head.

 

[BlueRidgeMark]

:agree2:

 

[Kicker_92]

The problem is..this 'just didn't happen' IMO. Too much timing, or low octane like water or wrong gas, old gas.

Just looking at your photos again...did you run the proper amount of oil in your fuel?

Are you sure this didn't have tons of hours on it..coupled with some preignition?

Thanks for all the great info! Your probably right that this was just a coincidence with getting stopped mid cut. The wedges in the cut slipped, the chain cut a groove and free revved for 4-5 seconds.

- We mix with stihl oil, and run at 40:1. Perhaps we should go with a little might oil, say 35:1?

- The engine did have a lot of hours on it to start with, and I've put on around 80 hours of milling time. When I say it's been running great lately, I meant for the last 10 hours or so. Had put in a new plug and washed out the air filter really well.

- Chain is sharp, fuel is about half full, and lots of bar oil. Not a lot of resistance in a 20" wide cut, but with the low rakers (8°) it wasn't screaming.

- I'm using 89 octane fuel, no more than 1 month old. We don't have any options here other than ethanol blends, so I try to not keep it around too long.


I'll try cleaning up the cylinder and hone it. If it comes up well then a piston & rings should do it...

 

[chuckwood]

honing?

- We mix with stihl oil, and run at 40:1. Perhaps we should go with a little might oil, say 35:1?

- I'm using 89 octane fuel, no more than 1 month old. We don't have any options here other than ethanol blends, so I try to not keep it around too long.

I'll try cleaning up the cylinder and hone it. If it comes up well then a piston & rings should do it...

I'm a bit paranoid and run around 30:1, no problems so far, however I do check for soot and carbon buildup from time to time.

I'm also paranoid with the 89 octane, and I mix 93 and 89 together to get something like 91 octane.

There's lots of threads and discussion on AS about repairing cylinders. What I've read, and what I've done, is to wet sand with 400 or 600 grit black wet sandpaper, the expensive stuff. I believe if you use anything more like a cylinder hone attached to a drill you risk breaking through the nikasil coating and ruining the cylinder. There's a thread about this right now on the chainsaw forum, a guy had a Stihl shop hone his cylinder, and they cut through the plating. There are photos with the post and you can see the contrast between the aluminum and the nikasil. I've found that hand powered honing isn't much fun and can take quite a while, you must wear heavy and uncomfortable rubber gloves. I used corrosive chemicals as the wet sanding agent, it seemed to work pretty well. I can see the temptation of trying one of those hones with all the little carbide balls attached to them. I've seen them advertised as being useful on 2 stroke motors. Maybe you only use one of those if you plan on having the cylinder replated.

 

[mtngun]

Andrew96, how does a chainsaw guy know when his saw has pre-ignition problems ? It is easily heard on a 4 stroke, but I've yet to hear pinging on a 2-stroke.

Unless his saw is modded, I doubt if the problem is too much compression or too low octane.

Correct me if I am wrong, but pre-ignition can be caused by heat -- if a hot spot on the piston or head ignites the fuel -- or by too MUCH squish. Saws rarely have too much squish, so that brings us back to heat.

Aside: my old SBC pings like crazy with only 8:1 compression. The culprit is poor head design with EXCESSIVE squish, typically 0.080"+. The preignition starts in the squish zone. I'm told that tightening squish to 0.040" will greatly reduce preignition.

I don't have your eye for spotting preignition, but what I see has "lean" written all over it. My saw's piston and dome are sooty, and sometimes caked with carbon. Kicker's piston and dome are way too clean.

Kicker, I'd try cleaning the cylinder with acid and maybe skip the sandpaper and hone. You might get by with just a new piston. But figure out why it was lean ! ! !

Sorry about your saw. Thanks for the pics. We'll all learn from your experience.

 

[huskyhank]

Just my opinion --

Make sure it has the right spark plug. I hope whoever worked on it put the right plug in.

After you put it back together, tune it in a milling cut. Lean it out until it runs fast then back to a very, very slight blubber - maybe even where its just clearing out after being under load for 10-15 seconds. Make a couple of cuts to get it hot and check it again. I'd call it perfect when its blubbery at the start of a cut but clears out after you getting going good. Do not ever run it any leaner than this when milling.

 

[SilverBox]

I don't have your eye for spotting preignition, but what I see has "lean" written all over it.

Yup. I'd vote for too lean myself, when it all goes back together run it PHAT!! . I like to hear a little four stroke in the cut myself, sounds like hell and I'm probably 1k rpm slower then I could safely be, but I know it won't lean seize.

 

[spankrz]

the standard line for a blown up saw. they bring it in, set it on the counter and say " she run better than she ever did till she quit". lean.

 

[rmh3481]

How many hours are on the engine? Could there have been an air leak? I would run a pressure test to see if there are any air leaks to know for sure.
http://www.arboristsite.com/showthread.php?t=112928

Dont use a hone. The plating is .003 thick. Use acid. Acid comes in drain cleaner, oven cleaner, brick cleaner or toilet cleaner. You can use any of these.

Spread out some newspapers, put the acid in a small glass and use a Qtip. Dab the acid onto the aluminum and allow it to bubble for a minute. Then rinse the acid out of the cylinder with cold water in the sink. Repeat until clean. Acid will not harm the plating. Keep the acid out of the ports and off the combustion chamber. As the aluminum dissolves into the acid, it will turn green.

Order a new piston kit from Baileys;
http://www.baileysonline.com/itemdetail.asp?item=QS+1124+030+2007&catID=

Fuel the saw with 32:1 mix and set the carb rich for future milling.

Best wishes,
Bob

 

[brncreeper]

Being an 'engine guy' and having raced..burned, broke many a 2 stroke motorcycle over the years...it's very easy to see what happened to your saw...even without getting a lope out and having a real look. Immediately I see two signs. Signs of detonation (preignition). Yes...very hard to tell on a 2 stroke until it fails if you cannot 'read' a plug properly with todays fuels. However...look at the photo up the cylinder. See the funny burn pattern? Less carbon in the intake side (cooler)..thats good, more on the exhaust side still OK....but look a bit closer...see the specs..the specs where the carbon is missing...the dot like marks. You ran this hot, and fast..but this was preignition that overheated the assembly and overheated (burned) the piston edge. There was more heat in that cylinder than you could cool off due to the ping. Look again at your piston photo. I know you took the photo to show a melted piston onto the rings..but look at the combusion pattern on the top..get your magnifying glass out..that's the key..that's what you should be looking at. On the exhaust side (of course..that's where the heat is), you can see the speckling again. Detonation has broken off the carbon deposits on your piston crown. The problem is..this 'just didn't happen' IMO. Sorry to tell you but look at the missing piston edge. Where did it go? It certainly isn't down the piston skirt. It's been burning off for awhile. Ping by ping. This should have shown up on your spark plug (don't just look at the colour...look for zits on it...speckles of carbon looking stuff..which is actually aluminum). As for a failure mode..well preignition for sure. I don't think getting the saw stuck (still don't know how) had much to do with it..other than some extra heat. This has been on a route to failure for awhile...at least for the last 10 - 20 minutes or so.
I think you'll be able to save that cylinder (if you're careful with the acid). I'd pull the crank and make sure there isn't anything, other metal debris down there. I'd then be checking your ignition timing. If that's fine and hasn't moved..then your fuel has water in it, is of too low an octane for your compression, or location, or (though I don't think so..without looking at your assembly under magnification) you just plane ran it too lean (lean doesn't usually = preignition though). Too much timing, or low octane like water or wrong gas, old gas.
Just my thoughts. I've only seen insides of various engines that look like this oh....say 250 times.....

Just looking at your photos again...did you run the proper amount of oil in your fuel? It's hard to tell from the photo but it looks like you have some galling on the piston pin? That's very hard to do...but could just be dirt from your fingers...or some other mark.
Kind of a lot of blow by for such a low compression engine. Are you sure this didn't have tons of hours on it..coupled with some preignition?
When you get it together....put a lope in your tool box to look at your spark plug (check for acne on the ceramic bit, electrodes).

Here's a new rule for you....If you're ever running an engine and all of a sudden it just decided to run really really great...remember to enjoy it since it's just about to fly apart. After a few failures you'll remember to shut it down pull the plug, get the lope out to read the plug.

As Paul Harvey would say: "The rest of the story", great observation and write up!

 

[BobL]

Could there have been an air leak? I would run a pressure test to see if there are any air leaks to know for sure.
http://www.arboristsite.com/showthread.php?t=112928

After reading kickers responses, my money is, it was on the lean side (ie mtngun's comment, Kicker's piston and dome are way too clean) to start with and then the saw developed an air leak.

I'm using 40:1 in much harder wood so it should not be necessary to run 30:1 - at t his ratio many of the additives in the lube are not burned and all it really does is fog the air around the operator with unburnt gunk.