Stihl MS 290 Engine Failure

[Wood Doctor]

Glad you guys are kicking this thing around. The owner bought the saw used. He has no idea whether these parts were aftermarket and neither do I. The input boot looks older, but that's hard to tell. The piston looks rather new and the exhaust side is unscathed. I have to wonder how long it takes a ruptured boot to generate enough heat to trigger snap ring failure. I suspect this happened rather rapidly and yes, the ring could have flown off on its own. I also noticed a worn crank seal but the bearings are still in fine shape.

The owner says he got his money's worth out of the saw. He used it on two or three tree removal jobs, so it lasted about 20 hours for him and ran like a bandit until the snap ring broke loose. He has no idea how long it had been run before he took possession, but the seller told him he had sent several tanks through it. In addition, if I rebuild it, I can keep it or sell it. Cosmetically, it was in rather good shape. Now it looks like an array of parts, like every clam shell 290 being rebuilt does and why nobody really enjoys rebuilding them. That includes me because it takes me four times as long to rebuild this beast than a Husky 350 or 353.

I really liked the forensic medicine post by TheTone. Kay Scarpetta could not have done better and neither could Maura Isles. Two thumbs up! But, the saw is not dead yet; I think I can resurrect it with a little luck, time, and skill.

 

[cuinrearview]

So it leaked at the seal and the boot, and a circlip busted loose. Hmmmmm..... surely OEM parts right @TheTone ?

 

[lone wolf]

How about the boot cracked and toasted the orig piston and cyl then someone put in a crap piston and bent the circlip too much installing it and it came apart?

 

[HarleyT]

Put up more pics!!!! Of the cylinder, other side of the piston, the rest of the saw!!!!

I am amazed how this overheated condition was isolated to only one of the circlips!!!

 

[Wood Doctor]

... I am amazed how this overheated condition was isolated to only one of the circlips!!!

So am I, but that is precisely what happened. The other side of the piston is normal with no scars. One of the crank seals is a bit worn. The small spring inside the seal is visible, but the seal is not in pieces. I imagine I could try to save the cylinder, but when you sink in 8 to 10 hours of work into a restoration, it srrms senseless to not replace it at the same time. The risk is rather huge.

If I ever get this saw to run again with good power, I'll do my best to post a Pic of the restored product.

 

[HarleyT]

put up a pic of the other side {exhaust} of the piston, please.

 

[dmb2613]

How about the boot cracked and toasted the orig piston and cyl then someone put in a crap piston and bent the circlip too much installing it and it came apart?

Gentlemen, that is what we call hitting the nail right on the head .
And by the way I can rebuild one of these little suckers in about 2 hours start to finish, I like em good saws for the money. You can make them run like a raped ape for pocket change. That is with funky dory parts. cost an arm and a leg with OEM stuff . I sell em to farmers and firewood cutters $300 a pop and guarantee them for 6 months
and I have NO unsatisfied customers.

 

[TheTone]

I really liked the forensic medicine post by TheTone. Kay Scarpetta could not have done better and neither could Maura Isles. Two thumbs up! But, the saw is not dead yet; I think I can resurrect it with a little luck, time, and skill.

That's the great thing about saws . . . throw in a few good parts and send them back into the game. Wish people were like that.

 

[grizz55chev]

Gentlemen, that is what we call hitting the nail right on the head .
And by the way I can rebuild one of these little suckers in about 2 hours start to finish, I like em good saws for the money. You can make them run like a raped ape for pocket change. That is with funky dory parts. cost an arm and a leg with OEM stuff . I sell em to farmers and firewood cutters $300 a pop and guarantee them for 6 months
and I have NO unsatisfied customers.

Turn an 029 into an 039, for around $50, easy Peazy!

 

[TheTone]

So it leaked at the seal and the boot, and a circlip busted loose. Hmmmmm..... surely OEM parts right @TheTone ?

I don't see where you could come to that conclusion from anything I said. Care to elaborate?

 

[dmb2613]

Turn an 029 into an 039, for around $50, easy Peazy!

New seals and Bearings if needed most of the time just seals. Punch out the muffler, cut the flywheel key about a 3rd richen up the H side and let it eat. Will run a long time for farmers and firewood cutters

 

[grizz55chev]

I’ve done a few, they are heavy, boxy, unbalanced, but homeowners love em!

 

[dmb2613]

And I put a cross pop up in em too , run like a 440 in 20 in and under wood, pull the hell out of a 25 inch bar too

 

[dmb2613]

Yes they do

 

[cuinrearview]

I don't see where you could come to that conclusion from anything I said. Care to elaborate?

Indeed

 

[dmb2613]

I do use Stihl Piston pin Clips

 

[HarleyT]

I do use Stihl Piston pin Clips

In aftermarket pistons? The groove/slot is the same?

 

[dmb2613]

No it is larger , but the clips fit tight and is good meat for the wrist pin

 

[HarleyT]

fit tight and is good meat for the wrist pin

Words to live by........

 

[Wood Doctor]

put up a pic of the other side {exhaust} of the piston, please.

As requested, along with the clutch side crank seal that is starting to show its spring:
Rings on this exhaust side seem to be in good shape -- a far cry from the input side as shown in Post #1. The circlip flipped a coin and then said, "I want to mess up the input side first." Then he jumped off the piston pin and went to work doing exactly that. He succeeded.