Scored Piston on MS290 Haunting me at night (pics)

[jmavro]

Hello,

First time posting here, but I have been reading the message boards on this topic for awhile.
I will try to keep this as short as possible.. Doing some post Sandy clean up with my MS290.. My 2 cycle mix can had straight gas in it from filling everything I had during the fuel shortage.. (here comes the "youuuu idiotttt" part) Ran straight gas through saw.. Saw stalled after about 30 seconds of cutting.. realized what i did, dumped fuel put proper mix in, put a little oil in the cylinder and restarted.. It ran fine but i did not try cutting with it. Fast foward to 2:30 am lying awake in bed thinking about it, I go back to the garage and remove the muffler. Piston is showing obovious signs of scoreing. I have not run a compression test on it yet (just ordered a gauge online, waiting for it to come) but im sure many of you can tell right off the bat how bad this looks. I am prepared for the worst and have been checking Balieys and found the fully assembled short block that would upgrade the saw to a 390. Being that I have never fully taken apart a saw before I did watch a few videos on youtube of a guy who completely breaks down a MS250 and re-assembles it. I have also obtained a copy of the service manual and have read every thread and posting regarding this saw i have worked on small engines before but for some reason am hesitant on this one.. Does anyone have advice on how I should proceed and if the short block is the way to go if im going to have to replace the p&c anyway? BTW.. went to my local Stihl dealer and they pretty much laughed to eachother tried to get me to give it to them to service and scoffed at the idea up upgrading to the 390.. From the postings I have read, I trust most of your opinions much more than theirs! Thanks for the help.

 

[H 2 H]

Welcome to the Jungle

 

[ResQGreen]

Welcome to the Jungle

indeed
it's like the other side of the looking glass
or turning your back on the dark side, if you're that worried about taking it apart, just take detailed pictures as you go, I've had my laptop on the workbench more than once. and get the plastic piston ring kit from baileys too, cheap and effective, almost worth buying a new one for each build, but I've used it for multiple engines to date.

 

[514mach1]

Meh. Just pop in a cheap piston (use the factory circlips) and clean the cylinder with some acid and 400 grit wet/dry. Should run you about $30 or so. If you want to be fancy, get Caber rings.

 

[Whiskers]

There's some good threads on here detailing complete teardown and rebuilds of a 290. They take a bit of time to get apart the first time around, but they really aren't that bad. I was able to save the cylinder in mine and slap in a new piston, otherwise it would have gotten the 390 upgrade. $150 to do drop in a 390 engine from baileys or have the dealer fix you up for a few bills. Not really a decision in my mind.

 

[TonyRumore]

I'm an amature when it comes to straight gassing a saw, but that sure seems like a lot of damage for only running 30 seconds.

Tony

 

[roger m]

there is a seller on fleabay selling new stihl long blocks for around $150 you can get U.S. cast or mahle.

 

[WidowMaker1]

is that a crack in the jug above the port im seeing, something looks Fubar

 

[roger m]

man,that close up looks real bad,i'm wondering if you have discovered an ongoing problem,i have seen a few 290's that friends of mine had that had scored pistons,and i know they had the correct fuel mix,i doubt that they had them retuned other than what they came set at the factory

 

[Dan_IN_MN]

Welcome to AS!

Check out my sig for MS290 help.

 

[nmurph]

You won't know if the cylinder can be saved until you pull it off. If the cylinder can't be saved I would go with the Baileys for price, power upgrade, and customer service. That definitely didn't happen with only 30 seconds of run time.

 

[sefh3]

In my signature line there are few threads to tear these saws down.

I think you have more issues than straight fuel. Check your fuel line. They are known for cracking and sucking air.

 

[THALL10326]

Hello,

First time posting here, but I have been reading the message boards on this topic for awhile.
I will try to keep this as short as possible.. Doing some post Sandy clean up with my MS290.. My 2 cycle mix can had straight gas in it from filling everything I had during the fuel shortage.. (here comes the "youuuu idiotttt" part) Ran straight gas through saw.. Saw stalled after about 30 seconds of cutting.. realized what i did, dumped fuel put proper mix in, put a little oil in the cylinder and restarted.. It ran fine but i did not try cutting with it. Fast foward to 2:30 am lying awake in bed thinking about it, I go back to the garage and remove the muffler. Piston is showing obovious signs of scoreing. I have not run a compression test on it yet (just ordered a gauge online, waiting for it to come) but im sure many of you can tell right off the bat how bad this looks. I am prepared for the worst and have been checking Balieys and found the fully assembled short block that would upgrade the saw to a 390. Being that I have never fully taken apart a saw before I did watch a few videos on youtube of a guy who completely breaks down a MS250 and re-assembles it. I have also obtained a copy of the service manual and have read every thread and posting regarding this saw i have worked on small engines before but for some reason am hesitant on this one.. Does anyone have advice on how I should proceed and if the short block is the way to go if im going to have to replace the p&c anyway? BTW.. went to my local Stihl dealer and they pretty much laughed to eachother tried to get me to give it to them to service and scoffed at the idea up upgrading to the 390.. From the postings I have read, I trust most of your opinions much more than theirs! Thanks for the help.

Looks like you may be under estimating the 30 seconds there. Thats alot of scoring for 30 seconds on pure gas. If your 30 seconds is correct it was scoring before the pure gas went in. Makes no nevermind, she's scored. You got the right idea, toss a 390 jug on it and go cut wood, its not hard to do. Here's some help for ya,
http://www.arboristsite.com/chainsaw/133453.htm

 

[1dragon]

Looks like you may be under estimating the 30 seconds there. Thats alot of scoring for 30 seconds on pure gas. If your 30 seconds is correct it was scoring before the pure gas went in. Makes no nevermind, she's scored. You got the right idea, toss a 390 jug on it and go cut wood, its not hard to do. Here's some help for ya,
http://www.arboristsite.com/chainsaw/133453.htm

To the OP THALL's right! The power difference with a MM, 390 kit, and properly tuned carb is very nice! I was upset that my factory piston broke UNTIL I fired up the 390 and cut with it. Gotta say I'm glad it happened now! I don't know how you are with tools but they are not hard to do. Just follow some of the excellent posts on it and you'll be fine.

 

[Rockjock]

I had exactly the same dilemma and the great help I received here made it all but a distant memory. Great people here that you can ask questions and get good answers. 1 bloke even took a brand new saw and began to tear it down just for the pics.. NOW that is what I call helping out. IF you get stuck just ask and you will have your answer in no time!

 

[Gushh]

She's a goner... I'd say that's at least about a minute of WOT under load with the straight gas. Try rebuilding it yourself, it's a great learning experience. If you can upgrade, go for it!

Also, what mix ratio do you normally use?, don't go for the green bs ratios, always add a bit extra of oil even if it means a slightly fouled plug or having to clean the carbon off the ports earlier (unless you use some magical additives in your gas) oil is the life of an engine.

I may need to replace the bearings on a small 26cc engine soon, the piston and rings should also be replaced... I noticed a small score mark on the cylinder, corresponds to the current piston, intake side ... could've been contamination from the intake that caused it?, too lean mix? (not trying to hijack the thread, just curious)... couple very fine scratches on the exhaust port side, but minute. It's loosing compression anyway through the damage on the intake side, clearly noticeable when you pour oil into the cylinder, seals it up momentarily. Couldn't feel any damage on the cylinder but I didn't remove it yet, maybe it's worse than it feels?

You can buff out all cylinders with lye or only if they're a specific type?, some people use acid?, assuming they've got alu inclusions on the walls.

 

[Stihlofadeal64]

Looks like you may be under estimating the 30 seconds there. Thats alot of scoring for 30 seconds on pure gas. If your 30 seconds is correct it was scoring before the pure gas went in. Makes no nevermind, she's scored. You got the right idea, toss a 390 jug on it and go cut wood, its not hard to do. Here's some help for ya,
http://www.arboristsite.com/chainsaw/133453.htm

Yeah what he said

 

[jmavro]

Wow, Thanks for the replies.. What a great tool this site is.

Thinking about my run time on straight gas, it could have been longer (and probably was) but the more i tell myself it was only 30 seconds the higher the compression gets on the saw.

I appreciate all the advice and will undertake the rebuild, I am actually looking forward to doing the upgrade to the 390 and learning the saw alot more. (Anyone have any issues with the Short Block from Baileys being aftermarket and made overseas?) Also besides the x27 torx driver, and clip to hold the piston rings is there anything else i should have handy? Again thanks for all the help.

Stand by for the next post on trying to tune the carb to the new engine.

 

[barneyrb]

At the WKY GTG it took (I think) 47 min to change the shortblock and have it running. Tree Monkey did it in under 30 at their GTG. It can be done quickly.....

 

[H 2 H]

Wow, Thanks for the replies.. What a great tool this site is.

Thinking about my run time on straight gas, it could have been longer (and probably was) but the more i tell myself it was only 30 seconds the higher the compression gets on the saw.

I appreciate all the advice and will undertake the rebuild, I am actually looking forward to doing the upgrade to the 390 and learning the saw alot more. (Anyone have any issues with the Short Block from Baileys being aftermarket and made overseas?) Also besides the x27 torx driver, and clip to hold the piston rings is there anything else i should have handy? Again thanks for all the help.

Stand by for the next post on trying to tune the carb to the new engine.

Take the limiters off the carb when you have the carb off the saw