Could I fix my Stihl MS 250?

I've ordered the parts (p&c) to fix an ms290 sitting in a box in my garage. $80 and however long it will take me. My time is free so I'm only out the parts cost. Ir'll be a learning experience for sure since I've never rebuilt anything bigger than a model airplane engine before.

I rebuilt my FarmBoss 290 with new piston/cyl from Ebay after my brother in law ran it with straight gas. On a 1 to 10 scale for some one who is handy and likes to tinker, I would put it at a 5. It is a great learning experience, and will give you a world of knowledge on chainsaws. However, before you go off buying parts for your saw you need to find out what destroyed your first piston & cylinder, good luck!

If you've got the time, a warm place to work on it, and you like the saw, go for it. It's fun to play and the risk is minimal.

S

There isn't to much to a 2 cycle engine( so to speak) no valves or head gaskets. I would dive into it . I myself am a big job guy and stink at tuning. If it were me put the cylinder on and have the shop fine tune it. The other great news is there is so much knowledge on this site that if you get stuck ask some questions .

I've never done it myself but I'm itching to try, just have to find the right dead saw. I think its a relatively simple procedure overall and while it mght take us twice as long as the guy in saw shop, I thin kits time well spend.

Since its dead anyway you have nothing to lose, so disassemble the saw and get the cylinder off the piston and get some good sharp photos of the damamge. If its not too bad you mgiht be able to clean up the cylinder with muriatic acid and only replace the piston and rings, whcih will knock the parts cost down considerably.

Take a look at the damamge and see where its ruined. Intake side damamge is debris getting in past the filter or in the gas, exhaust side damamge is too lean, or stragiht gas damage or an air leak (which causes a to lean condition).

If you opt to not fix it let me know what you want for it, maybe we can work something out. I've never owned a Stihl and it could be a fun winter project.

thinkxingu said:

If you've got the time, a warm place to work on it, and you like the saw, go for it. It's fun to play and the risk is minimal.

S

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Warm place is key! :cheese:

I can't tell you what your time is worth.

if you got tools and time, then I say "do it".

Get a good workspace and take the entire thing apart, if you decide that it was just too complicated to do that, then don't buy the new P&C and pack the parts in a box and sell them on ebay (or send me or Mayhem a PM) and you are no worse off then you are right now.

If you decide it wasn't as bad as you thought, then we'll direct you to replacement parts and help you any way we can over the interweb while you reassemble it!

let me know if you need a service manual and parts list. i think I have them somewhere on this computer (dad has a MS250)

this doesn't look so bad, does it?


BTW, that leads me to a cool thing I've been doing on my saw projects. If you go to the mailing supplies isle of your local store, then you'll find a big roll of brown paper for like 10-15 bucks (it's been a year since I bought it). it is a perfect fit for my work table and you can spread parts all over and draw circles around them and make labels and write notes, etc etc. It's awesome. Then when you are done with it, you rip it off the roll and throw it away. pretty much works like that white paper doctors use on their examination tables. If nothing else it keeps your table from being ruined with oil and gas (the paper absorbs most, but not all of those things, so still be careful)

donmattingly said:

. The guy also said with all the crap they put in gasoline these days, it has a shelf life of about 14 days. I will be more vigilant now.

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What ever.

Danno77 said:

this doesn't look so bad, does it?

BTW, that leads me to a cool thing I've been doing on my saw projects. If you go to the mailing supplies isle of your local store, then you'll find a big roll of brown paper for like 10-15 bucks (it's been a year since I bought it). it is a perfect fit for my work table and you can spread parts all over and draw circles around them and make labels and write notes, etc etc. It's awesome. Then when you are done with it, you rip it off the roll and throw it away. pretty much works like that white paper doctors use on their examination tables. If nothing else it keeps your table from being ruined with oil and gas (the paper absorbs most, but not all of those things, so still be careful)

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Perfect, now keep everyone far away! :lol:

so, what did you decide? gonna try it or not?

Danno77 said:

so, what did you decide? gonna try it or not?

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Looks like a piece of the case and fuel tank. Only seeing four screw I think there should be more of those as-well.

smokinjay said:

Danno77 said:

so, what did you decide? gonna try it or not?

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Looks like a piece of the case and fuel tank.

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not you, ya dork! I was wondering if Don was gonna try to fix his 250!

I asked Pen to split our fun game off of this thread, but he couldn't. I'll start a new one so I can stump you!

Danno77 said:

smokinjay said:

Danno77 said:

so, what did you decide? gonna try it or not?

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Looks like a piece of the case and fuel tank.

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not you, ya dork! I was wondering if Don was gonna try to fix his 250!

I asked Pen to split our fun game off of this thread, but he couldn't. I'll start a new one so I can stump you!

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lol, Whats all missing?

Glad to hear it. We can definitely help you if ou need it!

Check your PM inbox...

donmattingly said:

Thank you for all the responses. The gentleman at the shop said it was most likely bad/old gas that killed the piston and cylinder which I believe. I remember the last time I used it after the October snowstorm, I just used the mix that could have been a couple of months old. The guy also said with all the crap they put in gasoline these days, it has a shelf life of about 14 days. I will be more vigilant now.

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The 'bad gas' line is typical of a bad shop/mechanic. Gas does drop in octane fairly fast, and with ethanol blended into it these days it can go bad over time. Unless you are dealing with marine engines, 14 days is a little fast for gas to go off. It shoud be fine for a few months in a land based tool like a chainsaw unless it is kept badly or exposed to heat, extreme cold, or water. I get gas to stay fresh for over a year, and can keep it fresh for up to two years. The simple solution for "bad gas" is in a small bottle on the shelf at your local auto parts or HW store. Its called Sta-Bil. It will do two things to keep your gas fresh; one is that it keeps the octane high so you will not get pre-ignition (engine knock) by keeping the lighter components in gas from evaporating away, and the other (more important these days) is that it will keep the ethanol in the gas from picking up water and separating out (phase separation) and doing damage to the fuel system and engine.

Before I go on, no I do not work for Sta-Bil or any oil or gas addative company. I use and swear by this stuff becasue it works. The trick to using Sta-Bil is that you need to add it as soon as you buy the gas, as it cannot restore the original octane once the higher octane and more volitile components like butane and propane have wafted away. There are two types of Sta-Bil, one is the older red formula which is the one you want for chainsaws, and the other is green that is for marine engines. Either will work fine though. Add it as instructed on the label, and you will never have bad gas, even if you leave it in your chainsaw over the winter season, you live in a humid climate, or if you have 10% ethanol gas like we do in Oregon.

As an aside, all Stihl saws made after the MS number changes sold in the US have been designed and tuned to run on crappy US grades of gasoline. Saws like Dolmar have had problems with being tuned at the factory to higher octane German gas and then imported and sold in the US and run with lower US octane gas without being re-tuned. You should re-tune your saw after filling it with whatever gas/premix oil that you use, and with whatever bar and chain you are running. Different length bars will alter the peak RPM of a saw, so you can overrev a saw if you tune it with a long bar and then put a shorter one on. I have also seen saws with scored engines that were tuned at high altitude and then brought down to lower elevation and run in denser air, causing a lean running condition leading to overheating. At 6,000 ft. elevation there is roughly 90% of the air that there is at sea level.

Which brings me to the issue of the two main causes of engine scoring in 2-stroke chainsaw engines. One is straight gassing them. You are basically one tank away from your BIL blowng the engine by filling the tank with plain gasoline. Without premix oil in the gas the friction increases rapidly and the engine parts rub and heat up and the piston, rings and cylinder become scored. The other main cause of engine scoring is overheating from running too lean. There are several possible causes of running too lean, the main one being that the H jet on the carb is set in too far not allowing enough gas in the mix at high revs. At WOT (wide open throttle) a saw should 'burple' or 4-stroke, meaning that there is enough gas in the mix to keep it from overheating. Other less obvious ways to run your saw too lean are removing the air filter and running a saw; tuning your saw with a dirty air filter and then cleaning it; tuning your saw with a dirty muffler screen and then cleaning it, running your saw at a lower elevation than where it was tuned (we are talking several thousand feet here); running your saw out of gas (at the last minute or so that the tank is drained the saw will typically run lean and rev higher); and gas line pinching and clogging. Also if you modify your muffler you will lean it out, so you need to retune the saw after doing so. Modifying the muffler on a newer Stihl saw will require your removing the carb H limiter cap and removing the limiter tab and putting it back into the carb so it can be tuned richer. Note that no service dealer can alter a saw legally, and if they come across a saw that has been tampered with (muffler opened up, cylinder ported, limiter tabs trimmed, etc.), they must correct it or reject working on it. That is the new federal EPA law.

Just some ideas about some of the things that are blamed on 'bad gas'....

A PS about bad gas...

Other problems that can occur to the engine due to gasoline are allowing it to rev too high, or running your saw with lower octane gas than it was tuned at. Each saw has a top rev max that the saw should be tuned to using a good digital tach. Going beyond that limit is apt to damage the saw. Note that the max rev factory numbers for all Stihl saws are actually 500 RMP lower than the maximum engineered red line for all their saws. So if you know what you are doing with a tach you can set your saw to run at higher revs (and get better performance without blowing up your Stihl saws).

Running lower octane gas can lead to engine knock (at the worst) but it may also lead to more subtle problems due to pre-detonation, cumbustion flaring, and uneven burning. These all can cause uneven pressure on the piston dome at TDC and may casue the pistion to slightly tilt to one side or the other, leading to scoring of the cylinder wall. In this case the term 'bad gas' actually applies. The result is engine scoring similar to overheating. The solution to this is to keep your gas fresh and use a gas stabilizer to keep the octane high. I also use premium gas in my saws. Higher octane will result in more even burning, and a more stable piston at TDC. I used to go to Washington State to get 100% premium gasoline there after they made all gas in Oregon a 10% ethanol blend. However, WA state now only has ethanol blended gas. 4% ethanol is all that is required to 'oxygenate' gas to lower smog levels in winter months, and that is typically what you see in gas in states like California (after they phased out MTBE). However, the corn lobby and green do-gooders all want more energy independance, so states like Oregon have gone overboard and passed laws that require 10% ethenol blends. As a result of this marine engines have had massive problems, as ethanol likes to absorb water. Once ethanol absorbs water, it likes to separate from the gasoline with the water and settle to the bottom in gas tanks, fuel lines and engines. Marine engine damage went through the roof here after they reformulated the gas here, and there has been a lot of backlash. As a result Oregon passed a law allowing for gas stations to sell pure premium gas for marine and off-road use. However, there is no mandate that they do that, so only a few stations sell the stuff and at a steep price (which is actually worth it in 2 stroke and marine engines).

Note also that while ethnol has higher octane that gasoline, it also has a lot less energy than gasoline. About 40% less. A 10% blend of ethanol will result in 4% lower gas milage in your gar, and a noticable drop in power. It results in the same power loss in a chainsaw. Keep in mind that more octane does not mean more power from gas, it just means that it burns more evenly. Historically it ment that you could run higher compression engines and get more power out engines using higher octane gas without getting pre-ignition. Some people I know use 100 octane LL AvGas in their saws, but that stuff has lead in it to get the octane boost. I would rather not be exposed to the lead in the exhaust running a chainsaw on leaded gas. Even small amounts of lead can do damage to humans. In my view, that is what I would call, "bad gas", even though it smells really good (lead tastes sweet to humans).

Great posts Stihlhead!

Blasket said:

Great posts Stihlhead!

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+2..great info

Stihlhead-excellent post! i was about to submit a post on what octane gas i should use in my stihl saws-old and new,but you summed it up perfectly! tomorrow i fill my cans with premium.i think indiana still has 0 ethanol premium-i'm 5 miles to indiana. i will find out first. will also be sure to use sta bil more religiously in the future. thanks a bunch! art

STIHL officially recommends a mix ratio of 50:1 high quality (89 US octane minimum) unleaded gasoline to premix engine oil. 89 octane is typically what is called 'mid grade gas' in the US. Octane ratings vary worldwide as to what the octane numbers mean and how they are determined. In the US, octane is rated as the average of the research tested (at the refinery when it is fresh) and the gas station tank tested (after it has been delivered by pipe, truck or rail or some combination thereof). Meaning that the octane rating here is the average between the best octane level that the gas will ever have and what it will typically be when pumped into your tank. So when gas is pumped into your tank it already is likely to have a lower octane rating than what is posted on the pump. Once it is in your tank, if left untreated, it will typically continue to fall.

The rate at which the octane falls is influenced by the time of year that the gas is bought, and the container it is kept in. The volatility of gas in the US varies as to the time of year that it is refined. In the US we have what is called winter gas and summer gas. Winter gas is more volatle (lower vaporization pressure) and tends to have more lighter components (mainly butane) that waft off easier. Summer blends are heavier and tend to be more expensive, because butane and propane are cheap but they have to add less LP gas in summer. Which is one reason that gas is more expensive in summer than in the winter. There are 20 or 30 different seasonal blends so the actual vapor pressure requirements vary by region, and all states have their own requirements for gasoline blending on top of that, making it rather complicated. In many regions they require (or used to require) the adding of an oxegenate to gas in winter to lower smog during air inversion times. In places like California, they used MTBE to do that, but that is now banned. So they use ethenol now as an oxygenate for reducing smog year round as well as to appease the corn/ethanol/green lobby.

I try to buy and store winter gas becasue it is lighter and better as well as cheaper. Bigger bang for the buck. It will bubble up plastic gas cans more in the heat. Plastic gas cans breathe more than metal ones do, and some recommend that you store gas in metal cans for that reason. I use both types myself. I have a staged system for premium gas for my 2-stroke powered tools. I buy premium gas in a 5 gallon plastic jug and add Sta-Bil as soon as I get it home. Highest priority; get that stabilizer in there. Now it will be good for a year. Then I pour it into two one gallon plastic jugs as needed and I add premix oil to at that time. Adding premix will lower the octane rating as well, but adding any heavier oil to gas will do that. I use Elf 100% synthetic oil that I get from a motorcycle shop. It has a blue color added so that you know if the gas has been mixed with oil. If my gas is clear, it is regular for the lawn mower or unblended super for the 2-strokes. I keep my regular gas in metal cans so that it does NOT get into my 2-stroke engines. All 2-stroke engines are only one tank full away from being scored by straight gas! I know way too many people that have straight gassed their saws to death. I have bought several of them and refitted them with new P&Cs;.

BTW; there is much debate as to what type and how much premix oil to use. I would recommend any 100% synthetic JASO FC or FD 2-stroke oil rated for air cooled engines. Do not use MARINE 2-stroke oil! Noooooo! That is TCW rated, and is designed to run in water cooled engines. It will work in a pinch, but it will gunk up an air cooled engine over time. Read: AVOID! Also avoid any non-rated premix oil or 'all purpose' generic premix oil. They are likely to gunk up your engine, muffler screens, and foul your plugs. The same thing will happen with JASO FB rated oil over time, as I have experienced using Castrol FB premix oil. I flipped to Mobile 1 100% synthetic years ago and I noticed the difference instantly. The saws ran better, revved higher, the muffler screens stayed clear, and the engines looked better when I tore them down. I have some friends that are gold certified Stihl mechanics and they all note that even using a dyno or dyno-syn mix oil FC rated leaves more residue in the engine than 100% synthetic. Mobile 1 is not sold here any more, so I flipped to using Elf.

Lastly there is the topic of how much oil to add to the gas. You cannot really go wrong with 50:1 as recommended. There is an old argument from us older 2-stroke enduro motocross riders that more oil makes for a better ring seal and better lubrication of the low end and hence more power. But there is a tradeoff in lower octane and less power buring more oil as opposed to gas, as well as more fouling. So I tend to use about 45:1 for slightly better ring seal, and to err on using a tad more oil than a tad less. Some run 100:1 gasil, but I would not recommend that.

Wow StihlHead... Wow... I think he's typed more in these 3 posts than I have in my last 100....

FYI: Lead is in 100LL AvGas for lubrication/valve seat wear issues amd doesn't contribute to the octane rating. The lead leaves behind deposits. Since the deposits keep coming, the lead never wears off the valve seats and that coating helps them seal up better too.

Many people here report great results using Star-Tron fuel additive for treating fuel against storage deterioration and phase separation.

Good points on the plastic cans breathing more than metal ones.

Excellent on nailing Marine 2-stroke oils being used in air-cooled engines. I've opened up a couple engines that were running marine oils and the burnt-on deposits are well, yucky. :lol: