Stihl MS271 Farm Boss engine failure

[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/...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...JEALw_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/18507065818...cAAOSwtKhhyL2i

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-...nt-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