Killed the MS880 while milling

[Andrew96]

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.

It's very hard to do. I seem to notice when going through a mode whereby you get high cylinder pressures but not high rpms..you can feel/hear it then. Snapping the throttle open when it's just off idle will create nice high cylinder pressures. You might hear it knock now. Way hard to feel or hear than on a 4 stroke since they have a lot of time (more revolutions) to spin down and make a noise. Suffice to say..you look for it with a 2 stroke..feel it/hear it on a 4S. You look for it on the plug under 4x or 10x maginification. Easy to see acne on the plug if you use magnification. Or make sure you give yourself lots of room for problems. Over octane is one way, fresh fuel, avoid enthanol.

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

Well I don't think so...he didn't have too much compression..he had too low an octane for that run. 1 month old gas he said...race gas can go 'off' in a day depending on how it was kept. Some guys have gas left in open cans in the sun...that allows some chemicals to flash off into vapour. That affects it's anti knock properties. A can left with the vent open will collect moisture in a few days..ruining it for hard core use. How long did it stay in the gas station? Was that tank full, empty, filled with water to saturation? Lots of things affect the fuels anti knock properties...I mean...he only started off with 89 which around here..is loaded with up to 15% ethanol. That's not going to help. (alcohol holds water, if allowed to absorb it, extra water screws up the anti knock properties of the fuel). There are also 'winter blends' sometimes distributed. Did the station sell him that?

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.

...yup that's a classic assumption....don't get caught up in it. Clean is not lean...burnt carbon...light coloured is lean (there are more good signs). Look at the colour of the carbon..it's not far off...there just isn't any. Where did the carbon go? It got cleaned off with preignition. Hammered off. Of course, that created extra heat. However, 2 strokes can deal with heat better than some 4s. They eat a lot of heat..then die fast. (the operator would have felt a super hot engine in his hands...or bobl would have popped a barbie lid when he saw his temp gauge numbers), 4s burn valves and run bad before a meltdown (exotic fuels aside). Want to see what his head should have looked like?...look at the side of the piston..the area under the top ring. Lots of blow by...the head should have had more carbon on it than that. Look at the exhaust port..starting to look 'normal' now? Lots of carbon in that assembly..just not in the chamber.

One of the hardest things I've been doing with engines in the last 15 years..is trying to read plugs/heads burn patterns with the unleaded pump fuels of today. They are hard. I've been reading plugs for a long time and I get stumped many times reading unleaded pump fuel. Harder than you think. Read a head or piston..same signs.

You might see lean....I still see fuel that has the wrong properties. We know he didn't change the compression..we know he didn't put a blower on it, no nitrous. It might have had ethanol in it (which I think should be avoided for non self regulating engines)..it wasn't new fuel, it had a proper mix with good oil. It was a month old, I'll assume a month sitting premixed. I wouldn't completely rule out a vacuum leak but it didn't do a 'lean' meltdown. He just put bad fuel in a 2/3 used up piston.

There is a lot more to a proper fuel mixture than just rich or lean..how much oil. Changing the oil ratio creates a lot of other changes. Running more oil (changing your ratio) to combat high heat so you don't have a meltdown can actually promote running lean (more oil in the fuel means less fuel in your volume). It's not something that you can just twist the needle and richen 'er up a bit..Oil burns at a different speed that fuel (usually slower so it hangs around). Read what the oil manufacturer wants you to mix it at...follow that unless you know 'why' you should change. Prepare to be wrong.

 

[Andrew96]

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.

Bob...being rather new at playing with stihl saws...I'm not familar with the properties of the plating. However, I doubt you'll find it's 0.003" thick. Maybe that was just a typo. More like 0.0003" thick. However....That's the way to remove the piston flesh from the bore. Qtips, acid and patients. Ha...no hone either...those are for iron bores. Just like you said...unless you are just going to hone it all off and then have to replate.

The rings are the mating parts here. That beautiful chrome bore you are lucky enough to have for cheap these days..doesn't want to be honed, sanded or otherwise @#$%ed with. Clean it up, new rings on a FORGED piston. Pull the trigger and hang on.

Sorry for the long posts guys. I've been absorbing info from here for a long time...at least now I'm on familiar ground.

 

[Kicker_92]

I should probably mention, all my engine experiance is with big V8 4s motors, the 2s repair world is quite new to me.

As far as acid goes, you'd mentioned a couple differant sources, is there a particular acid to look for on the label?

Assuming I can get the cylinder to clean up ok, is there anything else to do while it's apart? On the 4s we'd usually take off any shrap edges or flash that can heat up and cause a preignite, and polish the exaust ports. Does that apply to 2s as well?

Our 89 gas is a 5% ethanol mix. I have the option at some stations of a 94 octane, but that has up to 15% ethanol in it. We'll go down to one gas can instead of two, that should keep it down to a week old max. Would you suggest mixing the oil in right away, or only as we need it? I think the Stihl mix has a stabilizer in it.

Will try the acid & q-tip to clean the aluminum off, just need to know which acid to use.


Thanks for all the help!

 

[DRB]

Bob...being rather new at playing with stihl saws...I'm not familar with the properties of the plating. However, I doubt you'll find it's 0.003" thick. Maybe that was just a typo. More like 0.0003" thick. However....That's the way to remove the piston flesh from the bore. Qtips, acid and patients. Ha...no hone either...those are for iron bores. Just like you said...unless you are just going to hone it all off and then have to replate.

The rings are the mating parts here. That beautiful chrome bore you are lucky enough to have for cheap these days..doesn't want to be honed, sanded or otherwise @#$%ed with. Clean it up, new rings on a FORGED piston. Pull the trigger and hang on.

Sorry for the long posts guys. I've been absorbing info from here for a long time...at least now I'm on familiar ground.

Not long winded at all.

I have enjoyed your input.

 

[huskyhank]

I should probably mention, all my engine experiance is with big V8 4s motors, the 2s repair world is quite new to me.

As far as acid goes, you'd mentioned a couple differant sources, is there a particular acid to look for on the label?

Assuming I can get the cylinder to clean up ok, is there anything else to do while it's apart? On the 4s we'd usually take off any shrap edges or flash that can heat up and cause a preignite, and polish the exaust ports. Does that apply to 2s as well?

Our 89 gas is a 5% ethanol mix. I have the option at some stations of a 94 octane, but that has up to 15% ethanol in it. We'll go down to one gas can instead of two, that should keep it down to a week old max. Would you suggest mixing the oil in right away, or only as we need it? I think the Stihl mix has a stabilizer in it.

Will try the acid & q-tip to clean the aluminum off, just need to know which acid to use.


Thanks for all the help!

I'd keep my gas as fresh as possible and mix just before use. I'd think about how I store my gas. Can that be improved on? Are you sure there are no options for non-ethanol gas where you live? I'd consider aviation gas if I was in a location where non-ethanol fuel is absolutely not available.

But here is the most important part -- I am pretty sure that if you had the high speed screw set just a bit richer you'd still be running your saw. So the main thing is to pay attention to the tune of your saw every time you run it. Check the tune every time you mill. I almost killed my big saw from a small air leak and not paying attention. I want mine blubbering a bit at least at the start of a cut. If its not, I want to know why.

 

[WadePatton]

op says he really cleaned up the air filter and the saw ran great between then and failure. if not re-tuned could that be the source of a lean condition? i'm no expert, i'm just asking.

i too am a burble freak.

 

[mtngun]

You can't trust month old gas ? Get real. In rural areas, people have their own gas tanks which they fill once a year. I use a 55 gallon drum, fill it in the fall, that's my winter supply. Usually there is some left over that I continue to use into summer. Yes, it does soak up water, which settles to the bottom and looks different than healthy gas. The last 5 -10 gallons from the barrel get dumped. Got careless and ended up with some of the watery, one year old gas in my pickup. It didn't like it one bit, but sputtered along.

I am more careful with gas for saws, though. Try to use fresh ("fresh" can mean several months old, instead of a year old. My "freshest" gas at the moment was purchased in November).

50:1 is recommended for EPA reasons. Some of the same saws, when sold in Europe, have a 32:1 recommendation. What does that tell you ?

I can believe that there was pinging, as evidenced by the broken piston edge, but it's a chicken or egg question. Did pinging lead to overheating, or did overheating lead to pinging ? I find it easier to believe that the engine was lean, either due to a leak or due to carb tuning, which made the piston too hot, and the hot piston edge acted like a glow plug and caused pre-ignition.

All theory aside, considering the value of an 880, it's worth buying a vac tester and tach to make sure things are right before putting the saw back to work. Check the fuel lines and fuel filter, too, maybe just replace them to be sure.

It's a darn shame about the saw.

 

[WadePatton]

i second the vac test notion.

only 088/880 i've ever seen (purchased new by a woodworker who free-hand slabs with it) has been to the shop twice for air leaks. (which cause lean conditions). i know it was a crank seal at least once.

 

[Andrew96]

You can't trust month old gas ? Get real. In rural areas, people have their own gas tanks which they fill once a year. I use a 55 gallon drum, fill it in the fall, that's my winter supply. Usually there is some left over that I continue to use into summer. Yes, it does soak up water, which settles to the bottom and looks different than healthy gas. The last 5 -10 gallons from the barrel get dumped. Got careless and ended up with some of the watery, one year old gas in my pickup. It didn't like it one bit, but sputtered along.

I am more careful with gas for saws, though. Try to use fresh ("fresh" can mean several months old, instead of a year old. My "freshest" gas at the moment was purchased in November).

The problem here is your comparing your situation with the OP and I don't think they are the same. I doubt your fresh November gas is stored in a plastic container...no you have it in a steel drum. Either way....I think the reasons your saw is alive right now has to do with your particular combination of lower compression, a well sealing top end, and you have chosen to run overly rich as your insurance rather than some other options, as many others choose too...but not our OP... Old fuel has to do with how it's stored. It would be less useful if it was kept in an open topped container. You store fuel just like the actual gas station does, then mix when needed. Not everyone does, sadly, not our OP.

I can believe that there was pinging, as evidenced by the broken piston edge, but it's a chicken or egg question. Did pinging lead to overheating, or did overheating lead to pinging ?

I think wear led to overheating. I feel the piston was too worn and leaking, that will help it heat up nice (as evidenced by the blowby). I also agree that burbly rich = cool so he could have still been running this if it was over rich. It would still have been pinging away though until he used other fuel. You cannot get around the clean combustion chamber, pre ign marks on the piston top and head. Would it be rich enough to overcome ping? Maybe but that would have to be pretty fat...there are many options to overcome the shortcomings of poor fuel (for that combination).

All theory aside, considering the value of an 880, it's worth buying a vac tester and tach to make sure things are right before putting the saw back to work. Check the fuel lines and fuel filter, too, maybe just replace them to be sure.

It's a darn shame about the saw.

Good discussion.....it's no fun to have a failure though, and that is a nice saw.
I might add that the fuel pump diaphram be checked for cracks..which will turn into/are leaks, another source of a vacuum leak though I think I made my failure mode clear.
No one seems to want to follow up on the timing issue. Having a solid state timing box fail offering up too much advance, or physically moving from it's fixed timing location would be a problem...follow right along with what I think happened.

 

[Andrew96]

I should probably mention, all my engine experiance is with big V8 4s motors, the 2s repair world is quite new to me.

I started with 2s then moved to 4s, I'm a consultant now for various builders we have around here (cars bikes, sleds, boats...only 1 aviation engine though). I get called in when they are stumped...or cannot get a good tune going.
The about the only difference is vacuum leaks. On a big V8 a vacuum leak causes some idle games, stumbles..all of which can be dialed out. A 2s...vacuum leaks just cause a meltdown. You cannot have any. You cannot just fire them up and see...you need to check first. If you play with v8s...get out your leak down tester..you'll need 1/2 of it.

As far as acid goes, you'd mentioned a couple differant sources, is there a particular acid to look for on the label?

What you are really after here is muratic acid...but almost any strong acid will work..that's why all the sources. If you are only going to use if for this project...get the smallest container you can. You're after about 50ml at most. I think you'll have to buy 1 liter though. Read the instructions though..it's real acid and will burn your nose eyes and skin..not to mention everything else.

Assuming I can get the cylinder to clean up ok, is there anything else to do while it's apart? On the 4s we'd usually take off any shrap edges or flash that can heat up and cause a preignite, and polish the exaust ports. Does that apply to 2s as well?

No...keep the files away from this one. I think you need to concentrate on how you're going to check everything so this doesn't happen again. Just because I guessed (based on a couple of photos) that you ran poor fuel in a worn top end...I could be wrong. There are tons of things you need to check.
Did some of your piston end up down near the crank? That needs to get cleaned out?
You need to check your crank seals don't leak..your case 1/2s (the block)..the whole assembly (the block plus intake manifold which is part of the cylinder) needs to be pressure tested...but I also vacuum test it (too many reasons why to go into here). You'll need to figure out how to do that with fittings and such. Read about it on the chain saw part of the forum.
How about your ignition timing. What's it's initial..does it curve correct?
Your fuel pump runs off vacuum...could leak.
Your carb base gasket..carb itself. I know it's just a small looking block..but everything runs off vacuum and needs to be sealed.

Our 89 gas is a 5% ethanol mix. I have the option at some stations of a 94 octane, but that has up to 15% ethanol in it. We'll go down to one gas can instead of two, that should keep it down to a week old max. Would you suggest mixing the oil in right away, or only as we need it? I think the Stihl mix has a stabilizer in it.

Warning...issuing free advice here!....I think you need to locate some other fuel source. Try anything that is ethanol free. Another gas station? Mix it on demand. If you can't I'd still go for 94 + ethanol over 89 + little less. Neither are the best choice though IMO.

 

[huskyhank]

And since the OP stated the saw had a new spark plug installed just before it melted down -- when you put it back together be sure to check the plug to see if its the right one for this saw.

 

[WadePatton]

i recalled that someone posted a laundry list of "acids" in this thread. oven cleaner and drain cleaner are not acid. they are base a/k/a lye. don't know if that makes a difference or not. the hardware store sells various acids.

i've used plenty of lye cleaning cast iron, but do not know which is preferred or if both will work on the aluminum here and not the nikasil.

 

[the westspartan]

How old was the gas you were running?

I teach college sculpture classes and bought an ms180 for the students to rough out shapes with. Ran like a top for the first semester(early spring). Was hardly ever used. Next semester(late fall) a student fueled it up before I had a chance to dump the old fuel from the can he was using. TOAST! in about a tank of gas it was toast. Piston looked just like this one.

I know these are very different scenarios (light use on homeowner grade saw VS heavy use on a beast of a pro saw) but I imagine bad gas would do the same in either situation.

Good luck.

By the way. I am very strict about freshening my fuel supply now. Lesson learned!

 

[BobL]

A lot of what occasional CS operators think is old mix is just old straight gas. I wouldn't trust any fuel that someone else mixed 6 months ago.

 

[the westspartan]

A lot of what occasional CS operators think is old mix is just old straight gas. I wouldn't trust any fuel that someone else mixed 6 months ago.

I agree! I don't ever use the school gas in MY saws, just in case. However, it was definately mix he ran through the 180 it was blue. LOL

 

[BobL]

i recalled that someone posted a laundry list of "acids" in this thread. oven cleaner and drain cleaner are not acid. they are base a/k/a lye. don't know if that makes a difference or not. the hardware store sells various acids.

i've used plenty of lye cleaning cast iron, but do not know which is preferred or if both will work on the aluminum here and not the nikasil.

Both strong acids and strong bases will work on aluminum but Muriatic acid or HCl is the most commonly used for this purpose.

 

[Kicker_92]

Muriatic is common as a pool/spa chemical, is it not?

I'll give that a shot and see what the cylinder looks like. Learned that the same piston is used for the 880, 088, and 084, so that helps.

While I have this open, any suggestions on improvements for a milling saw? Was thinking of keeping the port timings the same, but widening and smoothing out the ports.

Any other improments for mid range power? What about thickening the base gasket to lower the compression a bit, reduce the chances of detonation?

 

[mtngun]

Any other improments for mid range power? What about thickening the base gasket to lower the compression a bit, reduce the chances of detonation?

I was going to suggest the opposite. More compression is one of the easiest ways to gain power.

But, the logical thing to do is check compression and squish after you bolt the new parts on. I assume you are near sea level, so you should see around 160 psi. If not, I'd be inclined to tweak it in that direction.

I'm not a 2-stroke guru but 4-strokes with aluminum heads can run 9:1 or 9.5:1 compression ratios on cheap gas. OEM Stihls seems to be 8:1 to 9:1, not exactly radical.

 

[Brmorgan]

Kicker, Canadian Tire has Muriatic (Hydrochloric) acid down in the paint/solvent dept (maybe around pool stuff too). It's in a white cylindrical container with blue lettering about 4" round and a foot high or so, and is kept wrapped inside a plastic bag for extra protection. It's not expensive; it's been a while since I bought mine but I think it was 6 or 7 bucks.

As a warning though, this is a STRONG acid. It fumes quite a bit, and if you leave it out in an open container it will very rapidly oxidize and corrode any nearby reactive metals. Be very careful not to sniff the fumes too - they can easily overpower you or burn your lungs; think of swimming pool chlorine but dozens of times stronger. If you get a bit on your skin, don't panic, but do wash it off with lots of water right away. Since water only dilutes acid and can't neutralize it, it can take quite a bit of water to truly wash all the acid away.

So sad for the 880. What was it blowing for compression before? I can't imagine a stock 880 having high enough compression to cause detonation / pre-ignition without there being another factor involved. Good ~91 octane should be good to near 200 PSI; I run it in my 180 PSI 181SE without any issues. And I'd be willing to bet there isn't a stock 880 anywhere that is running that high. If it definitely isn't fuel/mix/carburetion/airleak related, and it turns out detonation was the true culprit, I'd also be highly suspicious of the new spark plug being too hot or the ignition being out of time for some freak reason.

This has been posted many times over in the chainsaw forum, but maybe not here in the milling hangout:

READING PISTON DAMAGE EXAMPLES

 

[Kicker_92]

Got most of the alum off the cylinder, it looks pretty good other than several small grooves through the plating. Even with the plting worn out a bit on that side, I'll put a new piston & rings in and run it for a while. Will clean up the exhaust ports a bit, and knock down any high spots.

I didn't do a compression test on the MS880, I've only measured the 385xp and it was around 140. I'll buy my own comp tester and check it when I get everything back together.

It's a good time to do a BobL style muffler mod too, since this is basically a milling only saw. The parts are all in the dishwasher getting cleaned up (I have a great wife!) so will start working on it this weekend.