Stihl MS271 Farm Boss engine failure

[Jeremy Chatterton]

I bought my MS271 brand new about 10 years ago and have put many MANY hours on it. It has been my "go-to" saw for every day use. A few days ago I was cutting some trees for firewood and had been running the saw for about 30-45 mins. It was running normally and then just quit. No indications of anything weird before the failure. It had plenty of gas and bar oil. It just QUIT! When I went to restart it, I could not pull the cord. I removed the spark plug and still could not pull the cord. I knew it was something internal and took it back to my garage. I have attached pics of the piston and the cylinder walls. It looks like something got into the cylinder and gouged the piston and cylinder wall. The gouge was way too deep to even think about re-surfacing/honing the cylinder. It was toast. My question to all of the knowledgeable folks on here is: What could possibly cause this to happen?? My fuel filter was relatively new, I think I replaced it last summer. It looked perfectly clean when I disassembled the saw and the fuel tank was really clean. I really can't figure out what could have caused this. Have any of you had this happen?
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[Tom M King]

Check the little roller cage bearing in the top of the connecting rod. Were the keeper clips on the end of the wrist pin? If it just shed a clip a piston and cylinder kit will put it back to work. If that little roller bearing is shredded, it will probably need a whole new crank assembly plus seals and cylinder kit, which puts the price of parts more than half the cost of a new saw. Check for slop in the main bearings while the cylinder is off too.

Only use OEM clips regardless of where the other parts come from.

Aftermarket parts are a lot cheaper, but they're a lot cheaper.

[Edward Weber]

Exactly what I was going to say, the photo sort of confirms it.

[Tom M King]

Thinking about this some more, I've never been in the bottom end of a homeowner grade saw. I understand they're not as easy to work on as a Pro saw is. I looked, and it's a $500 saw. If you need to buy a new one, I suggest treating yourself to a MS261cm. It's a couple of hundred dollars more, but a Pro grade saw, lighter weight with more power than the 271.

I googled for a comparison and found this: What is the difference between ms261 and ms271?



The 261 is a mag case, easier to work on and rebuild, more power, lighter. The 271 is more plastic, heavier, and a little more difficult to work on for the avg joe at least. The 271 if probably fine for the avg joe that justs cuts a little firewood.

[Larry Frank]

Were the rings intact when you took it apart? A broken ring could cause such damage.

[Brian Elfert]

Thinking about this some more, I've never been in the bottom end of a homeowner grade saw. I understand they're not as easy to work on as a Pro saw is. I looked, and it's a $500 saw. If you need to buy a new one, I suggest treating yourself to a MS261cm. It's a couple of hundred dollars more, but a Pro grade saw, lighter weight with more power than the 271.


A $500 chainsaw is considered homeowner grade? I always thought the homeowner grade saws are the $200 to $300 saws, and $500 gets you something pretty good.

[roger wiegand]

A $500 chainsaw is considered homeowner grade? I always thought the homeowner grade saws are the $200 to $300 saws, and $500 gets you something pretty good.

For $tihl you need to move the decimal point over ;-) they strictly control their retail pricing, no discounts. Good saws, though, even the "homeowner" grade-- they will run rings around the cheap saws from the Borg.

[Brian Elfert]

For $tihl you need to move the decimal point over ;-) they strictly control their retail pricing, no discounts. Good saws, though, even the "homeowner" grade-- they will run rings around the cheap saws from the Borg.

I was thinking about chainsaws in general, not just Stihl. I have an inexpensive Echo chainsaw, but it won't start after sitting with fuel in it for years. I have been using a cordless chainsaw instead.

[George Yetka]

I hate to be the guy but how much do you use the saw? I switched off the stihl to a milwaukee 3 years back and have sleep better not having to maintain any 2 strokes anymore. My issue was that I used it a couple times a year and was borrowed a couple times a year. So everytime I used it I would have to put a new blade on it and half the times I would have to overhaul it to get it running.

The milwaukee is super fast do to the narrow bar and chain and with 2 big batteries you can cut for a couple hours.They do overheat so you have to swap back and forth every 10-20 minutes. The stihl I gave to the family so if anyone needs to borrow they have to get it running if they want it.

If I were using a saw weekly or more than I would still use gas or if I was cutting very large stuff

[Tom M King]

Those cordless saws are easy to start, but they won't do this to a dry Maple. I thought I'd just be cutting Pines that a big blow blew down across our trails that day, but we came up on this dead maple, so I just used the saw I had set up for Pine. This a hot rod 066 pulling a 10 tooth sprocket.

https://www.youtube.com/watch?v=R2cdN53BxGs

[Edward Weber]

I have a 270, the precursor to the OP's saw. It's been running fine for 20 years. They are a good quality saw, period.
As always, depending on how often you use your saw and the type of cutting, it may be worth while to simply rebuild it.
A new cylinder kit and a few other parts can have it like new for less than $200, in most cases.

[George Yetka]

Those cordless saws are easy to start, but they won't do this to a dry Maple. I thought I'd just be cutting Pines that a big blow blew down across our trails that day, but we came up on this dead maple, so I just used the saw I had set up for Pine. This a hot rod 066 pulling a 10 tooth sprocket.

https://www.youtube.com/watch?v=R2cdN53BxGs

Tom I agree that is ideal to have a nice saw setup like that I just wasnt using it enough and everytime I had it tuned and sharp someone would borrow it to cut roots(always so dull when it came back). But I did cut up a 30" tree last summer with the Milwaukee.

[Tom M King]

I like cordless saws for some things too. I keep a little one and a polesaw in my truck toolbox. I like to use them when up in a lift bucket too instead of having to start a gas one.

I keep a couple of saws for loaning out. I tell whoever wants to borrow one that they are hard to start. They are.

[Maurice Mcmurry]

I bought my MS271 brand new about 10 years ago and have put many MANY hours on it. It has been my "go-to" saw for every day use. A few days ago I was cutting some trees for firewood and had been running the saw for about 30-45 mins. It was running normally and then just quit. No indications of anything weird before the failure. It had plenty of gas and bar oil. It just QUIT! When I went to restart it, I could not pull the cord. I removed the spark plug and still could not pull the cord. I knew it was something internal and took it back to my garage. I have attached pics of the piston and the cylinder walls. It looks like something got into the cylinder and gouged the piston and cylinder wall. The gouge was way too deep to even think about re-surfacing/honing the cylinder. It was toast. My question to all of the knowledgeable folks on here is: What could possibly cause this to happen?? My fuel filter was relatively new, I think I replaced it last summer. It looked perfectly clean when I disassembled the saw and the fuel tank was really clean. I really can't figure out what could have caused this. Have any of you had this happen?
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That looks like a classic case of gas only to me.

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[Edward Weber]

I keep a couple of saws for loaning out. I tell whoever wants to borrow one that they are hard to start. They are.

loaning out :confused:????
no tools lent out, to anyone, ever
(this is an entire thread itself)

[Tom M King]

Those are the only tools I loan out. I got tired of telling people I don't loan chainsaws or tools. I don't loan tools. We have mostly city folks with lake lots near us. There is almost zero chance that anyone could hurt themselves or anything else with one of these. They ran the last time I used them. I don't say that might have been over 30 years ago. I don't have time to work on them.

[Maurice Mcmurry]

Never borrow a gas can is another good rule.

[Adam Herman]

That looks like a classic case of gas only to me.

514867
i have the same saw, and that was my first thought also.

[Maurice Mcmurry]

i have the same saw, and that was my first thought also.

Yup, It is always right at the port, where temperatures and friction are at their highest.

[Alex Zeller]

I had the same thing happen to my Dolmar. Ran great for almost an hour and then the power went. I could pull it over but it was hard. I ended up replacing the piston and cylinder. My saw was a $1000 saw so spending a couple hundred on it wasn't a hard decision. I was told that it's possible that the oil and gas started to separate and for the first half of the tank I burnt too much oil. As the tank got emptier and emptier the ration leaned out. I don't know if it was true but it didn't really matter.

I try to remind myself to shake up the saw before using it now. Often I'm not cutting near the house or if I am it's because I cut a number of trees down a couple of days earlier. So either the ride into the woods will mix it up or there's not enough time for the oil and fuel to separate. Had your saw been sitting for some time?

[Ole Anderson]

Jeremy, I see this is your first post to the Creek, welcome! Out of curiosity, have you posted this question on any arborist or chain saw forums? Wondering how you ended up here? BTW I have a MS 018 and a 290 Farm Boss that has served me well. It always helps if you complete your information so we see your location in the header.

Anybody else follow the Chicanic on YouTube? She repairs nearly a thousand small engines per year including a ton of chain saws. Here is a great episode about an MS 311. https://www.youtube.com/watch?v=XKcqp43HVvI&ab_channel=Chickanic

[Jim Becker]

I never realized there was a "smaller" version of the FarmBoss...mine is the 290 version, bought in 2000. It's been an amazingly reliable tool.

[Bill George]

I wonder if he was using Ethanol and got water in the gas then it would run lean with no oil?

[Alan Rutherford]

Jeremy, I see this is your first post to the Creek, welcome! Out of curiosity, have you posted this question on any arborist or chain saw forums? Wondering how you ended up here?...

I can't answer for Jeremy but there is no where else he could have found the depth of knowledge on almost any subject in the universe in a bunch of down-to-Earth people you find here. Pick any 10 or 20 topics in the Off Topic fourum and see what I mean.

[Edward Weber]

I never realized there was a "smaller" version of the FarmBoss...mine is the 290 version, bought in 2000. It's been an amazingly reliable tool.

Smaller is a bit unfair, it's really just an evolution.
All the Farm Boss models are in the 50cc range, similar weight, and roughly the same hp. It's really just a platform/engine change every so many years. The numbers fluctuate a bit but it's really just a trade off. A few tenths of hp loss for a smaller lighter engine is really all it's been.
Power to weight ratio is pretty much the same.

[Jim Becker]

Oh, I understand and agree about that Edward. I just didn't know about the alternative version with the .271 vs the .290

[Edward Weber]

Oh, I understand and agree about that Edward. I just didn't know about the alternative version with the .271 vs the .290

There will probably always be a Farm boss, it'll just be a little different every so many years.
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[Jim Becker]

Oooh...a widdle qkewtie one.... :) :D

[Tom M King]

One other thing to consider before gambling on a cylinder kit would be to do a pressure test. A 2 stroke depends on keeping crankcase pressure up to a minimum level. If a saw is old enough for the crank seals to leak the least bit, the saw can get to the point that it's running lean, and can get lean enough that not enough fuel is getting to the cylinder walls which causes it to overheat.

To do the pressure test you hook a gauge that you can pump up in the spark plug hole and put plates over the intake and exhaust ports. You can slide the intake one in between the carb and the cylinder.

We haven't heard back from the OP, but if that saw ran lean, I would just replace it rather than spend money and time back into it.

If it has leaking seals, I understand they're harder to replace in a homeowner saw. Pro saws have cases that you can easily split for bottom end work.

Stihl used to have a third category called something like Farm and Ranch. The 290 was in that category. Those saws were build heavy expecting to spend their lives bouncing around in the back of a pickup. They had about the same power as the Homeowner line saws of the same size. I don't remember when they dropped that category.

The homeowner saws are mostly sold in places like hardware stores where they may or may not have someone that knows much about working on saws. The Pro saws are sold in shops where they have trained people that know what there is to know about keeping a saw running. Some shops may sell the whole line, and some may only sell the Pro saws who mostly deal with pro loggers. That's probably changed by now too though.

[Tom M King]

I did a google search for "pressure test ms271 youtube" and this is the first of many videos that showed up. I didn't watch any of them, so can't answer any question on a particular video.

https://www.youtube.com/watch?v=kZglEFo_HV0

[Edward Weber]

One other thing to consider before gambling on a cylinder kit would be to do a pressure test. A 2 stroke depends on keeping crankcase pressure up to a minimum level. If a saw is old enough for the crank seals to leak the least bit, the saw can get to the point that it's running lean, and can get lean enough that not enough fuel is getting to the cylinder walls which causes it to overheat.

To do the pressure test you hook a gauge that you can pump up in the spark plug hole and put plates over the intake and exhaust ports. You can slide the intake one in between the carb and the cylinder.

We haven't heard back from the OP, but if that saw ran lean, I would just replace it rather than spend money and time back into it.

If it has leaking seals, I understand they're harder to replace in a homeowner saw. Pro saws have cases that you can easily split for bottom end work.

Stihl used to have a third category called something like Farm and Ranch. The 290 was in that category. Those saws were build heavy expecting to spend their lives bouncing around in the back of a pickup. They had about the same power as the Homeowner line saws of the same size. I don't remember when they dropped that category.

The homeowner saws are mostly sold in places like hardware stores where they may or may not have someone that knows much about working on saws. The Pro saws are sold in shops where they have trained people that know what there is to know about keeping a saw running. Some shops may sell the whole line, and some may only sell the Pro saws who mostly deal with pro loggers. That's probably changed by now too though.

Stihl, continues to have three categories of gas powered saws, Home, Farm & Ranch and Professional.
https://www.stihlusa.com/WebContent/CMSFileLibrary/InstructionManuals/chainsaw_comparison_chart_2014.PDF

Not everyone can just, "replace" a $500 dollar saw, budget is always a consideration. The OP mentioned that the saw just quit, without any indication. This does not "sound" like a slowly leaking crank case. If anything, the rubber intake tube can crack and leak causing the lean condition, if that was indeed the issue.

Also, Stihl is only sold by authorized dealers

[Tom M King]

edited to add: I was mistaken. There is still a Farm and Ranch line. All my saws are old and I haven't looked at new ones in over a decade. That 066 in my video was new in 1997, if I'm remembering that correctly. https://www.stihlusa.com/products/chain-saws/

Yes, all dealers are authorized, but they all don't carry pro saws. Our close by Ace hardware does not. The pro shops stock the pro saws and might have a few of the smaller howeowner saws. The pro shops around here don't want to bother with homeowners that use a saw once in four years. The Ace hardware will be glad to sell them another saw.

I was just saying it would be worth checking the crank seals before putting more money in it. All you need is a couple of flaps of rubber, a kit from Harbor Freight, something to plug the impulse line with that's probably just laying around, and a spark plug hole adapter.

https://www.amazon.com/Vacuum-Tester-Bleeder-Automotive-Adapters/dp/B073CNGMRG/ref=asc_df_B073CNGMRG/?tag=&linkCode=df0&hvadid=312094794461&hvpos=&hvnetw=g&hvrand=2116021592531404762&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9009808&hvtargid=pla-567457242226&mcid=d426d2b17f423fa38510d3a3cd78d447&ref=&adgrpid=62497261819&gclid=Cj0KCQiA5fetBhC9ARIsAP1UMgGO0twBfCNJ-gF-nUqMuySVQaDhQu4QqaOc7Wxf-K6GcJGoRYcO51YaAsKJEALw_wcB&th=1

I don't know which size threads the spark plug is, but you can probably find a single one of these for less than the cost of two:

https://www.ebay.com/itm/185070658189?hash=item2b1712228d:g:XVcAAOSwtKhhyL2 i

If it's been running lean from a leaking crank seal, there is probably other damage and would be a poor bet for putting money in it for seals and cylinder kit. It's a fairly common thing that burns up saws. That one looks like to me that it ate a clip from the two gouges, which means there was probably something else going on causing it to run hot. The two deep gouges didn't just come from no lube. It could have been caused by straight gas, but that usually just scores the piston and cylinder that sometimes can be resurfaced it it doesn't cause it to lose too much compression. No fixing this one shown here. Could be a number of things from straight gas to a leak somewhere.

Guesswork often costs more money than necessary. If a cylinder kit is put on it, it might well only run for a little while and it crashes again. If indeed it does have more extensive damage than just the piston and cylinder, a new saw will be the cheapest way back to work if you have to pay someone else to work on it.

[Tom M King]

A little bit more about running lean in case anyone is reading this looking for information.

A 2 stroke running lean may seem like it's running fantastically. When running lean, if not too lean, it will rev higher faster when not under load like having the chain in a deep cut. For just cutting small stuff and branches it might seem like it's running better than it ever has. When in a deep cut though it will bog down and not have the power to make the cut.

That's one reason they took the carb jet ports off the homeowner saws. When someone adjusted the jets so it seems like the saw revs better it might just be leaned out a little too much.

They still have the adjustment ports on the Pro saws that aren't computer controlled. The Stihl saws with a CM on the end of the model number are computer controlled. I don't know if it's still the case but some pro models were sold in both regular carb controls and computer controlled. You could buy both an MS261 and an MS261CM. At first there was a lot of resistance from pros for using a computer controlled saw, but as they have gotten used to them they are mostly well liked.

Notice when I sat that 066 on the ground idling that it was not running the absolute best. It's a ported saw (hot rodded) so doesn't like to idle anyway, but I have the jest adjusted so it is running as rich as possible and not shut down. I can't idle it down all the way without the chain moving a little bit, especially with that 10 tooth sprocket on it, so I set it in leaves for a little extra friction.

In short, it's easy to be fooled by a saw running a little bit lean so if a crank seal or something else starts to leak a bit the saw may seem like it's running better than it ever has.

[Ronald Blue]

A little bit more about running lean in case anyone is reading this looking for information.

A 2 stroke running lean may seem like it's running fantastically. When running lean, if not too lean, it will rev higher faster when not under load like having the chain in a deep cut. For just cutting small stuff and branches it might seem like it's running better than it ever has. When in a deep cut though it will bog down and not have the power to make the cut.

That's one reason they took the carb jet ports off the homeowner saws. When someone adjusted the jets so it seems like the saw revs better it might just be leaned out a little too much.

They still have the adjustment ports on the Pro saws that aren't computer controlled. The Stihl saws with a CM on the end of the model number are computer controlled. I don't know if it's still the case but some pro models were sold in both regular carb controls and computer controlled. You could buy both an MS261 and an MS261CM. At first there was a lot of resistance from pros for using a computer controlled saw, but as they have gotten used to them they are mostly well liked.

Notice when I sat that 066 on the ground idling that it was not running the absolute best. It's a ported saw (hot rodded) so doesn't like to idle anyway, but I have the jest adjusted so it is running as rich as possible and not shut down. I can't idle it down all the way without the chain moving a little bit, especially with that 10 tooth sprocket on it, so I set it in leaves for a little extra friction.

In short, it's easy to be fooled by a saw running a little bit lean so if a crank seal or something else starts to leak a bit the saw may seem like it's running better than it ever has.

Many people have no idea what a 2 stroke engine sounds like when running rich or lean. Setting it so it's got what I call a slight "blubber" to it is not hard though. If a warmed up engine wants to bog when you give it throttle off idle then the low speed screw is to lean. When the "smog" motors came out the adjustability went away with the very limited adjustment available. Battery power meets my needs these days.

[Tom M King]

This site has the best information on such adjustments that I know of.

https://www.madsens1.com/carburetor-adjustment-on-pro-saws

[Ole Anderson]

Interesting that the OP has not returned yet to rejoin the conversation.

[Earl McLain]

Interesting that the OP has not returned yet to rejoin the conversation.

That may be the case, but this has been a very informative thread and i'm sure i'm not the only one who has benefitted from it!! Thanks to all who have commented.

[Tom M King]

That Madsen's article titles it as if it's for Pro saws only but all older saws used to have the same sort of adjustments on the carburetor and were tuned the same way. They used to, and may still have somewhere on their website, a simple outline of steps for the tuning process but I didn't look for it. I keep a copy of that in the little box I carry for saw sharpening with the chainsaw stuff.

edited to add: I looked for it but couldn't find it. If anyone wants to study more about chainsaws this looks pretty complete:

https://www.madsens1.com/chainsaw-tips-tricks

And this in particular applies here:

https://www.madsens1.com/piston-seizure-on-pro-saws