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MS 381 Piston Damage - Is this OK?

Started by NoobMike, September 18, 2017, 02:29:22 AM

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NoobMike

Hi Guys,

Forum and chainsaw noob here, feeling really dumb, embarrassed and let down (by myself).
Just got myself my first chainsaw, and first day in, I accidentally ran straight gas through it before I twigged that my 2-stroke can didn't have any oil in it... dahhh.
I am absolutely kicking myself and haven't had the balls to tell my wife yet...

Thinking back to last summer, I now realise why it didn't have 2-stroke fuel in it, but that isn't making me feel any better now...

So I purchase a Stihl MS 381. The shop filled the tank before they gave it to me (with 2 stroke mix - cos they ain't as dumb as me). They also filled the chain oil, and convinced me to buy the Stihl oil with the saw to get an extra 2 year warranty.
I had a small to medium sized well dead and partially rotten tree in the back yard.
Took it down and finished the first tank of 2 stroke. Well when i say finished, I do notice that there is always about maybe 1/5 of a tank left when it cuts out. Anyway at this point the stupidity kicks in and I fill up with straight gas from my 2-stroke can and continue on my way.
I ended up putting 3 tanks of straight gas through it before I noticed the colour was not blue..at which point I had a mild panic attack, stopped the saw, filled it with ACTUAL 2-stroke mix, ran it a bit to get the oil through, turned it off and started googling what the impact might be.

Now the general consensus is that even a couple of minutes with no oil will likely kill your piston and maybe cylinder, often with seized engine.
During this whole time, I did not notice any difference in performance, noise and certainly no seized engine.

I took the exhaust cover off and inspected the piston and to my surprise there is very little damage, and none that i can see to the rings. 

I'm after some advice from anyone who knows more about these things than me, on whether or not this damage is significant enough to warrant getting it serviced / fixed, or if it should be fine.
Secondly, if it should be fixed, what sort of cost would i be looking at for genuine parts.

What is the risk in not getting it fixed?

Below are two photos, as well as a link to a clearer video of the piston.



  



 




video (~80Mb)
https://www.dropbox.com/s/40ye0gf4spb59d7/Piston.MOV?dl=0

Thanks in advance, and please avoid any negative comments about how stupid it is to do this to a saw.. I am already aware of that and beating myself up enough.

ladylake


Straight gas will score the intake side also, maybe pull the carb off and have a look.  The exhaust side looks good to me.   Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

NoobMike

Thanks for the reply Steve.

From all the googling I did, I was under the impression that worst damage would be on exhaust side. Is that correct?
It's much trickier to get a look into the intake side on this saw. It seems like i'd have to take half the saw apart.
I was kinda hoping that I could assume less damage than the exhaust side...

If there is concern around needing to check that, perhaps I should just take it into the shop?
Thoughts?

thecfarm

Wait until you put chainsaw oil in where the gas goes and wonder why it won't start.  ::)
Welcome to the forum.
I have a gas can marked chainsaw. Nothing else is put into it or used for besides the chainsaw. I put the oil in first. If it's cold,the oil is warmed up first,could be brought into the house. I think it flows better when warm. I let the oil bottle drain into the chainsaw gas. I probably let it drain out for a half our. I want to get every drop. Than off to the gas station I go to fill it up with gas. I myself use the highest octane I get can. But that is another whole thread on that one.   :D
I do hope you are wearing chaps and other safety gear.
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

blueberrymuzik

From the pics you posted, it appears that you were very lucky. It looks as though you stopped cutting before any significant damage. If it were mine, I would run it and never forget how close you came to a disaster.

ladylake

 

Straight gas will score the piston rather even all the way around so it should be good ..   Running lean it will score at the exhaust port.  Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

sawguy21

That doesn't look like excessive damage, I would keep running it as is. Just make sure the carburetor is properly adjusted, they come lean out of the box.
old age and treachery will always overcome youth and enthusiasm

HolmenTree

Mike, welcome to the forum.
Getting er running and check the compression, then get back to us.
Get 2 readings 1 cold and 1 warmed up.
Making a living with a saw since age 16.

Woodcutter_Mo

 You may have lucked out and it may be just very well broke-in. I would get a separate gas can to use specifically for mix fuel.
It may not hurt to add a few drops of oil into the cylinder to make sure it's lubed before starting it again though I'd get a 2nd opinion on this.
Also may not hurt to check the compression after running it with some fresh mix fuel to prevent potential further damage in the case that it simply needs a new ring installed.
Those are just my thoughts, a 2nd opinion on this would be good.
-WoodMizer LT25
-592XP full wrap, 372XP, 550XP, 455 Rancher, RedMax GZ3500T
-Fixer-uppers/projects:
024AV, MS260, MS361, MS460, Shindaiwa 488, 394XPG

NoobMike

Thanks for the replies all.
I don't have means to do a compression test, but testers don't appear to be too pricey. Might check that later.

I dropped past the Stihl repair joint (without the saw) on my way to work and showed them video and asked their opinion. The guy was very surprised to hear that there were 3 tanks of fuel through it and said if it still idles fine and is running, don't worry about it. He nearly fell of his chair when I told him it was running fine.
He was actually very dubious about the possibility of getting 3 tanks of straight fuel through it without it seizing and being completely f'ed up.

Seems that I truely have dodged an expensive bullet (and possible divorce) here.. :-)

Perhaps the cold weather, sharp chain, soft tree and gentle use saved it... In either case it will NEVER happen again..

I do actually have a separate can just for 2 stroke. It was previously just for my brush cutter.
Problem came about because my other can that was just for the 4 stroke lawn mower started leaking last summer, so "in the interim" I filled up my brush cutter can with lawnmower juice so I could finish the lawns... Well clearly I forgot about that by this spring..

Ada Shaker

Being a new saw you may have just worn the rings out a little before any damage to the piston skirt. I would definitely get a compression test done and consider ring replacement. If the rings overheated it may effect the longevity of the engine. Just food for thought, even though it runs ok now, the rings may have a reduced life expectancy. Best to talk to your stihl dealer.
If it hangs to the left, your likely to be a Husqvarna man.
If it hangs to the right, your likely to be a Stihl man.
Anything else is an uncomfortable compromise.
                             AND
Walking with one foot on either side of a barbed wire fence can become extremely uncomfortable at times.

Texas-Jim

If it will start and run smile and dance a bit, now it likely shortened its life but at least it will run. If the shop serviced out with ultra oil it very well could last a minute without mix in it. Lot depends was it completely empty or did you top it off? We all argue over oil ratios but that synthetic oil does help at any mix ratio.
What we do in life echoes through eternity.

luvmexfood

Quote from: thecfarm on September 18, 2017, 06:06:15 AM
Wait until you put chainsaw oil in where the gas goes and wonder why it won't start.  ::)
Welcome to the forum.
I have a gas can marked chainsaw. Nothing else is put into it or used for besides the chainsaw. I put the oil in first. If it's cold,the oil is warmed up first,could be brought into the house. I think it flows better when warm. I let the oil bottle drain into the chainsaw gas. I probably let it drain out for a half our. I want to get every drop. Than off to the gas station I go to fill it up with gas. I myself use the highest octane I get can. But that is another whole thread on that one.   :D
I do hope you are wearing chaps and other safety gear.
Been there done that. Poured out the bar oil, little mix and shook and poured out then oil/gas mix. Fired up and smoked just a little at first.
Give me a new saw chain and I can find you a rock in a heartbeat.

Kbeitz

This kinda reminds me of the day my brother was driving his VW dune buggy over a rocky mountain
and knocked his valve cover off and lost all his oil. He filled the engine with water out of the creek and
drove 10 miles home with no engine damage at all.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

teakwood

National Stihl Timbersports Champion Costa Rica 2018

sawguy21

I have to wonder what was in the water. ;)
old age and treachery will always overcome youth and enthusiasm

Maine372

where are you that you can get a 381 new? how much does it resemble the original 038?

thedoublejranch

Keep in mind, as the pressure drops in the crankcase (the fuel goes there first on its way up through the transfer ports to the topside of the piston) the oil falls from suspension from low pressure and lubricates or coats the parts.

So the fact you had fuel with no oil, there was a nice coating and of course, it was probably pretty thin by the end of that second tank. Worst scuffing will be exhaust port side as this is where most of the heat is. 2 cycles are very inefficient and over fuel (run rich/fat) and run cooler than a 4 stroke and with the oil coating, though thin, still some there, you may be fine.

At this point, I would run it, if it runs fine, produces good power, no noises, then you are probably OK, any damage will show up in short order if there was any. You have more than cylinder to deal with, there is crank bearings and both rod bearings, small and big end.

You probably always has a small amount of fuel left with oil, so the ratio may have been real thin, but good synthetic oils can be run super thin. I wouldn't go over 50:1 (2.6 ox per gallon) but that's just me. Good luck, dont tell the wife, EVER.  ;D
The Double J Ranch & Timber Farm.
Member "NWOA" National Woodland Owners Association"

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