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Is ths ms 290 piston toast ? etc

Started by chainsaw_louie, March 02, 2011, 07:04:18 AM

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chainsaw_louie

Hi,
Could you fella's please take a look at these pictures and tell me:
   a) is the piston toast, the score marks don't look too good
   b) can I assume that the cylinder is gone too?  On a typical rebuild, do you just do the cylinder automatically when the piston is scored or  does a scored piston not necessarily mean the cylinder is bad too.  Probably need to pull off the cylinder and have a look before deciding

    c) How are the non OEM piston/cylinders for these Stihl saws, I looked at Baileyonline but didn't see a rebuild kit for the ms290
 






Thanks,

Tim

Al_Smith

A 290/029 is a solid block.no removable cylinder .That example in the picture  is just a pile of partially usable parts ,sorry .

lumberjack48

That's new to me to me Al, i have never seen a saw you can't replace the head and piston on, but I've been out of the pic for 15 yrs.
WOW ::) that's what you call a melt down

Looks like it was run with straight gas or she really got hot, held full throttle with a dull chain.
The saw never did run right, you can tell by the carbon build up, set to rich or gas was wrong mixture.

I've seen them this bad, do to my wonderful help, new head and piston, back on the job the next day [ If parts are on hand] 
Third generation logger, owner operator, 30 yrs felling experience with pole skidder. I got my neck broke back in 89, left me a quad. The wife kept the job going up to 96.

lumberjack48

One more thing, another reason this happened, i'll bet the screen is plugged in the muffler, no way to get rid of the heat.

When i bought a new saw, the spark arrestor was the first thing to come out.
Third generation logger, owner operator, 30 yrs felling experience with pole skidder. I got my neck broke back in 89, left me a quad. The wife kept the job going up to 96.

Al_Smith

Quote from: lumberjack48 on March 02, 2011, 10:54:37 AM
That's new to me to me Al, i have never seen a saw you can't replace the head and piston on, but I've been out of the pic for 15 yrs.


 
Most if not all of the Stihl consumer grade saws have been clam shell design for years . They do okay for what they were designed for but for all practical intents are not rebuildable .The price for the parts would be more than  the value of the saw .

FWIW there are numerious saws built by different manufactuers using a type of clam shell design .

lumberjack48

I looked around a little bit, i could fix it for about a $100. in parts, i did my own saw work, its the labor that kills you
Third generation logger, owner operator, 30 yrs felling experience with pole skidder. I got my neck broke back in 89, left me a quad. The wife kept the job going up to 96.

Al_Smith

I think most meet their death exactly like that one .I suppose if the cylinder would clean up it could be saved .New piston and rings maybe .It could have pulled tramp aluminum into the crankcase though contaminating the bearings .

Never the less it will have to be disected to the bones to further evaluate  the damage .Anything less is speculation .

Saw Dr.

Strip it down and get the bare cylinder in your hand.  Read up an using muratic acid to remove the aluminum transfer.  Take your time and do it right.  I have rebuilt dozens of 290's.  More than half of the time the cylinder can be saved.  Aftermarket pistons work fine and are cheap.  DO NOT hone the cylinder to remove the transfer, use acid.  Once it is clean, check for grooves.  little ones don't matter, but if it is big enough to catch a fingernail you might want to look for another jug.  Scratches above the exhaust port roof are the ones that really matter. 

If the crank seals are suspect plan on replacing them.  OEM are VERY expensive ($17 EACH!!!) but are the best.  There are some folks pawning aftermarket seals for these that are much too thick to fit into the machined groove in the cylinder, so beware of that.  factory seals are 4.4mm thick.  Good luck.
I don't try to explain to others why I play with chainsaws.  For those who already know, no explanation is needed.  For those who do not, no explanation is POSSIBLE!

Super 250

chainsaw_louie

Thanks everyone for your comments and suggestions.  I'll proceed with the teardown and see
what the cylinder looks like on the inside.  If the saw is junk, I might as well learn how they
engineer these things, I paid $50 for this saw so may as well get a lesson for my money.

Tim

chainsaw_louie

Hi,

I took the MS290 apart and took some pictures to get your opinions of the the condition.  My inexperienced opinion is that its not too bad because the rings are not sealed to the piston and the intake side of the piston and cylinder is clean.  I am thinking that the cylinder can be salvaged.  Regarding the comment by Saw Dr. that the scratches above the exhaust port  are the worst ones, it looks like there are just a few of those but I really dont have anything to compare the scoring/marks to .

I read posts on cleaning up cylinders and a lot of  advice is to polish off the crud (aluminum?) with 600 grit paper and oil.  But, if Muriatic Acid is the way to go ( Saw Dr.), then I'll pick up some of that, probably a friend has some, it shouldn't take much, you just dab it on with Q-tips and let it work?

Tomorrow I'll call over to the stihl dealer and see what  parts will run. I figure that I need piston + rings + crank seals + sealant.   I know that I can get a new short block for about $150, so thats my mark to beat.

intake side of pistion


Top of piston


Exhaust side of piston




Intake side of cylinder


Exhaust side of cylinder


Thanks.

Tim






sharkey

If you find that the cylinder is grooved too deply and is through the plating, Fish sells the oem 290 long blocks on ebay for around $120.  You would just bolt the new long block into your frame and go.  Long block is piston, crank, seals, cylinder and bottom pan all together and ready to run.  All new stihl parts, if you need a link send me a pm.     

Al_Smith

Well it's not my call because it's not my saw .However you have 50 bucks in a pile of parts, another 120-150 in a short block .So $200 more or less in a 290 that will still  be a 290 no matter what you do to it .

roostersgt

Yeah, he'll have only spent $200 on the most popular "mid" range saw Stihl produces / sells. Not a "pro" saw, but I doubt he really needs one anyway, unless he's using a saw everyday to earn a living, or simply desires bragging rights. I'm very pleased with mine and would buy another without hesitating. His saw is a bargain if he get's it fixed with just a new cylinder kit, or even an entire new R&R of the engine. I'm exited for him and his project. Please keep the pics and progress coming.

Steve
Stihl MS 170 14"
Stihl MS 260 Pro 16"
Stihl 028 Super 16"
Stihl 028 AV 16"
Stihl 028 AV 16"
Stihl 029 18"
Stihl MS 290 20"
Stihl 036 Pro 25"
Homelite Super 2 (mint)
Remmington 10" Tele Pole Saw
Troybuilt / Honda 27ton Logsplitter

Stihl Team Six - Sacramento Unit

chainsaw_louie

Agreed ,  I should never have paid $50 for it , but it was a friend so it seems like the right thing to do at the time. Thats considered a long term investment in generosity!  Next time $15 will be more like it.  

In the name of just seeing whats possible, I am real tempted to clean up the piston skirt, get the rings free and clear, clean up the cylinder and put it back together again and see if it runs.  I'll of course check the crank for holding pressure on the reassembly. I've heard that 2 cycles are forgiving of a tight fit in the bore, so the fact that my piston skirt is a bit scored may not matter.  If it don't run very well, I'll just re-do it .

The problem seems to be that the aluminum transfer on the cylinder wall doesnt allow the rings to seal against a smooth, even surface.  Once I clean that off  and if there are no scratches, I may be fine.  My cost is zero so I am tempted to try it.  Got to get the muriatic acid tomorrow, HD didnt have it  today.
 

Al_Smith

Easy off oven cleaner will work also .

There are several new pistons on flea bay relatively cheap if you can get the cylinder cleaned up .

chainsaw_louie

Thanks Al,  the oven cleaner is great.  It works slow enough that I can use it to clean
up the outside of the cylinder too.  I've just been leaving it on for 15 minutes at
a time then I wash it off with warm water and toothbrush.  It also takes the carbon
off the top of the piston and the cylinder.  I'm thinking that I should leave it on
longer to get all the carbon, but I don't want it to eat at the aluminum either.

I tried the oven cleaner on some of the plastic parts and its pretty effective at breaking down the
oil+sawdust+dirt crud that gets on everything.  The main body of the saw is pretty much covered
in that crud and oil so it will get the oven clean treatment too.  I am not sure how the wires, coil and rubber will feel about oven cleaner but I'll keep it away from those parts for sure.

I got a gallon of muriatic acid yesterday, smallest they had.  After I'm done with a
few more cycles of the oven cleaner, I may hit  the cylinder walls with the acid to get
any remaining aluminum off.  

Here are the results so far, not a huge difference from the same pic at the beginning of this post but I can feel with my finger that the cylinder walls are getting smoother and the rough edges are disappearing. Also, you can see the carbon coming off  :




Tim

Al_Smith

Get a 3M green pad and work on that tramp aluminum around the transfer ports .

You might try sanding the piston but it looks pretty far gone to me .What happens if you leave big deep grooves in the piston is it breaks the surface tension of the microscopic layer of oil  on the piston skirt .Then you get metal to metal contact,not good .

chainsaw_louie

Thanks Al I just saw you post about the 3m pad, but  I'd already done all I can do with 600/800 grit paper and muriatic acid.   Any aluminum is is gone.  There is a small round pit in the nicosil but mostly its smooth and even.  I cant catch a fingernail on anything in there.  See pic below, its kind of hard to tell whats what because the glare and reflection but thats as good as its going to get.



Now the piston is another story, the scoring on the exhaust side has left ridges along the skirt. I polished it as smooth as 600/800 grit paper could make it, but the ridges remain. 



These rings are probably the real no-go of this, I tried to clean them up but they have top to bottom gouges and scratchs that will probably not allow them to hold pressure.




If I could get just as set of rings, I would be tempted to try that , but it may just be throwing good money away .

Your thoughts?

Tim

Al_Smith

You can buy a piston for around 27 bucks on flea bay,rings for around 8-9 . Do what you like but I wouldn't do anything with that piston except use it for a paper weight .

jteneyck

I had a MS290 in about the same condition as yours.  The saw really wasn't that hard to disassemble, as I'm sure you know by now, and the cylinder cleaned up about the same as what yours looks like.  I put in an aftermarket piston/ring kit for around $35, and a used crank as well because the bearings felt rough in the original, for another $35 or so.  The saw has run great for 3+ years now.  So if you can get by with just a new piston - go for it.  The MS290 is a good saw for anything short of pro usage.  And do be sure to check the muffler for blockage before you put it back on.  Finally, check out some other threads about trimming the carb. screw limiters and retuning the carb. to avoid frying the new piston.  Good luck. 

scottedward58

I've got a spare 290 motor that's just collecting dust if you want it. It's practically brand new, it's seen some use but the cylinder and piston look almost brand new except for a little carbon. That I'd be willing to let it go.

chainsaw_louie

Thanks fellas, I went ahead and ordered an aftermarket piston for about $33 and two crank seals for $35.

The new seals have the same part number stamped in the rubber as the old seals do  but they look different and I just want to make sure that I got the right ones.   The difference is that there is this cover on the new ones that is smaller ID than the crankshaft but is flexible, do I just grease them up and push them on and does that disc just flare out around the crankshaft ?

This shows the disc ...new (L)  old (R)


This shows the reverse side of the seals new , old


Thanks,

Tim

bill m

I think you have the sides of the new seals reversed compared to the old ones.
NH tc55da Metavic 4x4 trailer Stihl and Husky saws

isawlogs

Quote from: bill m on April 13, 2011, 08:13:53 PM
I think you have the sides of the new seals reversed compared to the old ones.
So do I !
A man does not always grow wise as he grows old , but he always grows old as he grows wise .

   Marcel

sablatnic

Look like ptfe seals to me. Will see, if I can look it up.

Can't find any service information about them at Stihl, but they do look somewhat similar to the ones used by Husqvarna on the 254 and 242 about 20 years ago. Should be installed with the flexible plate on the inside, well greased / oiled. (I used 2stroke oil on the Huskys).
Husqvarna stopped using them as they were a bit harder to install than the normal seals, but they will last for ever.

Good luck.

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