Chainsaw died;

[oldballs]

This is a 11 year old Farm Boss Stihl MS290. It has been quite dependable and I have taken good care of it even though it has a lot of hours on it.

A couple days ago I was cutting a 30 inch White Pine Stump close to the ground so as to get my Stump Grinder on it. I have done this many times.

The bar is 20 inch, so I was working my way around it when all of a sudden it just died. In checking it out I can see nothing wrong...except that it seems to have not much compression when I pull the rope. It won't fire at all. Any ideas??

Cheers,
Mike

 

[Wagtail]

Have you checked the screen? Carbon build up (wire brush removal of any residue) is a quick check.

 

[oldballs]

Thanks Wag. The screen was clear/clean....as I usually keep it that way.
Cheers to you Wag
Mike

 

[MoKelly]

Do you have a gauge to check compression when you pull start? That can tell you if it’s an internal issue.

Good luck.

MoKelly

 

[oldballs]

Heck, I think I have a gauge for some old car engines around here somewhere....but I really don't know much about it other than routine maintenance. I wonder what the compression should be, just in case I get into it. I can see the piston go up/down thru the exhaust/muffler hole. Maybe the piston has rings??? I don't pretend to be much more than shade tree mechanic.

Thanks Mo

 

[ericm979]

Turn the crank so the piston skirt is visible through the exhaust port with the top of the piston right at the top of the port, take a good picture and post it here so we can look at it. If it's seized it'll usually show damage on the exhaust side piston skirt. That's the hot side so it goes first.

Compression should be above 120 psi. With a small engine like this you need a compression tester that has a Schrader valve in the hose at the spark plug end. Some don't.

 

[dodge man]

Check the spark plug first, make sure it hasn't started to come out. I’ve attached a pic of a MS250 that had piston damage. As bad as it was, it still had decent compression and ran but idled badly. This looking in the exhaust port.

 

[oldballs]

Thanks gents. I'll get back to you with a pic. Already checked the spark plug....cleaned again and gapped a different one. Will look for my compression tester.

Right now having problems with my eyes i.e. macular degeneration, cataract and waiting on a call from the doctor.

Cheers,
Mike

 

[thclimer]

If you hold the saw by the handle of the pull cord with only the weight of the saw does it unwind the cord rather quickly (5 sec)? Its a crude test but I have seen the weight of the saw unwind the cord and it a pretty good indication of poor compression.

 

[oldballs]

Okay guys,....still waiting for the eye doctor office to return my call. You know how that goes

So I went outside to do the above cord test that "thclimer" posted. It took about 6 seconds for the weight of the saw (without the bar & chain) to drop to the ground....tested several times.

Then with the sunshine I got some pics....some not very focused. It may be better to buy a new saw that take this one to a repair shop....Geeze I would hate to do that.

My compression tester is just a rubber hand held device with no Schrader valve.

Cheers,
Mike

 

[thclimer]

I had to edit my post to correct the wording, but it sounds like you got the idea.

To me 6 seconds, especially without the bar and chain sounds like poor compression, hopefully others will give their opinion.

 

[ericm979]

Pics are poor but I see that it seized and the piston (at least) is toast. Which is what I expected from the description. You can see the marks on the piston in the 004 pic. It also looks like the rings are missing? Maybe just the direction of the light.

The 290 is a clamshell design. That's where there is a plastic frame and the engine is a single casting that includes the head, cylinder and top of the crankcase. There's a metal cover that covers the bottom half of the crankcase. The whole thing bolts into the plastic frame.

If you want to fix it yourself you can get a complete engine from Farmertech: Aftermarket Stihl MS390 MS290 MS310 029 039 46MM Engine Motor Cylinder Piston Kit Crankshaft Assembly 1127 020 1210, 1127 030 0402, 1127 021 2500

Or a genuine Stihl: Genuine STIHL MS290 029 OEM Complete Longblock Motor Engine STIHL 46mm for sale online | eBay

(that one has a pic that shows what the rings should look like through the exhaust port).

You'll want to verify that that's the correct part. Sign on to arborsite, find the "Beg for manuals" thread and ask for the MS290 IPL and shop manuals. That will give you the parts list and instructions on how to work on the thing.

If you want you can disassemble the engine and inspect the damage. If you're lucky the cylinder will be unscathed and not too worn. Then you could replace the piston, rings (and while you're there the wrist pin bearing) and of course the circlips, reseal the bottom cover and run it.

Of of course if you don't want to deal with it you can buy a new one. I'd want to know what caused it though. #1 cause is accidentally running straight gas. #2 is air/fuel mix was too lean. The crown of the piston often shows it when that's the cause. Your piston damage extends to the crown which makes me think that's probably it. Saws can run lean because the carb was adjusted wrong or the crank seals are leaking and sucking air, or a few other things.

 

[oldballs]

Dang Eric.........that's quite a report and helpful. I thought that the rings were missing when I first looked in there....not knowing what to look for. Sounds like I'm looking at a new one....probably a MS291. With all my health issues I'd be forever getting that 290 rebuilt. The gas mix is the same that I have used the past couple gallons or so....and the carb settingd have not been deliberately adjusted.

The eye doc just called to set me up for a new appointment ....and probably some cataract surgery. I guess at 88 YO some of my parts are wearing out too.

Cheers,
Mike

 

[thclimer]

I think Eric confirmed your saw is in need of being rebuilt. I hope you were able to get some good use out of it it before this. I think if it was me and in your circumstances I'd buy a new one, sometimes you can invest a lot of effort and money into a rebuild, but I can understand if you enjoy that type of work as it can rewarding to fix it yourself.

I hope your eye appointment is soon and goes well.

 

[oldballs]

There's gotta a place in heaven for TBN'ers who are so helpful for others.

Cheers,
Mike

 

[ericm979]

You're welcome! I've gotten a lot out of TBN, it's cool when someone can use the obscure knowledge I do have.

You might look into the MS261CM. It costs more but it will be lighter and easier to pull start due to the compression release. The Mtronic electric carb auto-adjusts the mixture. I have it's slightly smaller brother the MS241CM and it's really sweet compared to the 025 (MS250 with screw caps) I was using for that size stuff.

 

[thclimer]

You're welcome! I've gotten a lot out of TBN, it's cool when someone can use the obscure knowledge I do have.

You might look into the MS261CM. It costs more but it will be lighter and easier to pull start due to the compression release. The Mtronic electric carb auto-adjusts the mixture. I have it's slightly smaller brother the MS241CM and it's really sweet compared to the 025 (MS250 with screw caps) I was using for that size stuff.

The 261CM is my favorite saw as well for the Hp to weight ratio its hard to beat. I've had one now for about 6 years and probably cut 25 full cords of firewood with it, always starts with 3 or less pulls and it just runs.

 

[dodge man]

I just rebuilt my MS250 a few months ago, Eric helped a lot and send me some manuals. It’s not bad to do but your heart needs to be in it. Mine looked similar but the rings were still there but the top one was fused to the piston. I spent about $100 doing mine. Your saw is worth more so worth a rebuild but not if you have to pay for it. My cylinder walls were scored and I bet yours are too.

I also THINK I ran mine with straight gas but can’t figure out how.

I also can agree a MS261 is a nice saw, I bought one a few months ago. Mine isn’t the CM model. It really cuts for its size and weight.

Good luck with the eyes.

 

[Bearsixty7]

I just bought my first Stihl last month at the local dealers annual spring sale, a MS261CM!

I have only used it to cut up about 3 trees at a friends to get them off his fences. Cold it starts on the 2nd or 3rd pull. When warm it will start on 1/2 pull. It does feel very light for a 20" saw but the best part is it has instant throttle response and it cut every tree like it was butter. The good/bad thing was it didn't spew saw dust, it was throwing sizeable chunks of wood! Needless to say I was grinning ear to ear after using it that little bit and very pleased with the money spent. Now if it is just trouble free for 20 years like my other saw has been I'll be thrilled.

 

[RandyT]

Pics are poor but I see that it seized and the piston (at least) is toast. Which is what I expected from the description. You can see the marks on the piston in the 004 pic. It also looks like the rings are missing? Maybe just the direction of the light.

The single ring in one location looks like it is missing due to the aluminum has smeared over it.