Basic Rebuild: MS 290

Once again we have a scored piston:



To know why it is scored a complete evaluation will be done. In this thread I will do the teardown and inspection.
The next thing off will be the carb, and to take off the throttle link does not require the handle cover to be removed. Just squeeze the throttle trigger and pop the link out of the trigger with a pair of needle nose pliers.



Then just twist it and unhook it from the carb.



Carefully push on the fuel line at the lower left, and the impulse line under the carb on the right, to loosen up these two hoses, and slide the carb off of the studs.



I have just found the first major fault on this saw. The limiter caps are missing from the carb. The base settings for the mixture screws with the limiter cap removed is one turn out from lightly seated. When I checked the H screw, it is only out ¼ of a turn. The L screw is out about ¾ of a turn. There is also a chance that these screws may vibrate out of adjustment on some models. The fact that the caps are missing means someone has been in here messing with the adjustments and the H screw is definitely in too far, which will cause a lean running situation.
The saw passed the pressure vacuum test, the tank vent is working properly, and the fuel filter is OK. It would appear at this point that the operator was under the misconception that more RPM meant faster cutting, and tuned the carb too lean.
Now the saw will be completely taken apart and inspected.
The black handlebar is removed by prying out the plugs from the anti-vibe buffers, and removing all the T27 DG screws holding the handle on.



Next the orange handle housing comes off. Using the lube fluid makes it easier to get the anti-vibe buffers out. Just use a small screwdriver to push back the buffer and allow a few drops to fall in. This also makes reassembly of the buffers and pulling any hoses back through the housing much easier.



Push the intake manifold back through the handle housing.

The handle housing will be flopping around now so be careful as the rest of the items attached to it are removed.
Disconnect the wiring harness from the master control lever by pulling the round connector out to the left, and undo the other wire and carefully pull it out of the groove that holds it in place. Make note of how it wraps up and back down in the slots.





Push the grommet out towards the engine and pull the wiring harness through the hole in the handle housing.



Remove the impulse hose by carefully pulling it back towards the engine.



Now insert the piston stop through the spark plug hole and very carefully feel it into place against the top of the cylinder wall between the top of the piston and the squish band. Do not let it slide on through the exhaust port. Bring the piston up to hold the stop in place and remove the flywheel nut and the left hand threaded clutch. The clutch will be very tight. Never use an impact wrench on an engine with a multi piece crankshaft in it. Always use a piston stop that locks up the engine at the edge of the piston where it is stronger. One that screws through the spark plug hole may poke a hole in the center of the piston, on late model high RPM engines.







Use a flywheel knocker tool threaded onto the crankshaft to separate the flywheel from the taper on the crankshaft. Screw it down until it just touches the flywheel, then back it off about one turn, and gently pry up against the flywheel from behind. It does not take a lot of pressure from the screwdriver behind the flywheel. Then hit the tool solidly with a hammer and the flywheel will come loose.

I now remove the oil pump, and chain brake mechanism if desired for cleaning.
In order to get the engine module out of the engine housing, there are four screws that go up through the bottom of the housing and pinch the engine pan to the cylinder while holding the whole affair together. There is also one bar stud, the rear one, that screws into the engine pan, and it has a thread locking compound on it and is very difficult to remove. What I do is lay some pieces of metal on the housing to act as a heat sink and protect the plastic from the heat I will use to soften up the thread locking compound. The oil passage nipple is right in this area and is easy to ruin if the heat gets near it.





I use a propane torch and very carefully heat the engine pan area where the stud goes in. A little heat is all that is needed, and then wait about a minute to let the heat soak in. The ribbed area sticking out from the pan is the area the stud screws into from the other side. Disclaimer: Flame and gasoline do not mix! Drain the tank and plug up the fuel line, clean off your bench, and do not blow yourself or your shop up!!!
I do not even try to save the bar stud. It will still be hard to remove, and locking pliers are needed to get a grip on the stud. There is not enough threads to try the double nut method. A new stud will be required. I borrowed a high dollar Snap-On stud tool one time to try this and it wouldn’t work either. Heat is the only way I have found to get the stud out. I would like to know if there is another way. The front stud is a DG thread screwed into plastic, and comes out easily. Remove it first so it is not in the way.





Notice the difference between the two studs, and how much thread locking compound comes out with the rear stud. The engine pan will need the hole cleaned out well and the new stud will need some fresh compound applied when installed. I use the blue stuff.
Now the engine is loose from the engine housing.
This is what is meant by STIHL when the phrase “engine module” or “modular engine design” is used. Pro saws have a split magnesium crankcase, like the 034 I did in another thread, with the cylinder held on from the top by four screws. A modular design holds the crankshaft in place to the bottom of the cylinder with an engine pan, and all the rest of the bits and pieces bolt onto the engine module.



This design allows for a lower cost of production, but results in a total tear-down to get to the piston and cylinder. There is nothing wrong with this design, it is just more labor intensive for service, and is used for saws that are considered home owner or occasional user models.
The engine pan is just stuck with Dirko, and comes off easily, then slide out the piston and crankshaft. Here is the exhaust side. This is a typical lean seizure, with the scoring starting in the middle and spreading towards the sides. It probably stuck and was restarted several times to do this much damage.





Notice that the intake side has no scoring at all. If the saw was operated on fuel with no oil mixed in, there will usually be scoring on both sides of the piston. Also notice the scuffing on the bottom of the intake skirt. Since a saw usually does not have a rev-limiter or any sort of constant load to hold the RPM down, as it goes lean the RPM goes up, and the piston starts slapping in the cylinder, and may have this polished look at the bottom. The exhaust side is hot anyway, and without the vaporization cooling that the missing fuel normally supplies, the piston overheats and melts, and metal transfer takes place.
The cylinder is very rough, so it is unlikely it can be saved.
A total waste of a good saw because the operator wanted to cut faster.
So once I gather enough parts I will show you how to put it together.

Great thread Eddie

Only thing I do alittle different is I don't heat that one bar stud up to take it out. I have the special Stihl bar stud remover socket. It goes over the stud, as you turn it it grabs the stud with tension and you can remove it without putting a mark on the threads of the stud. Sadly this specail socket costs around 50.00 but its worth every penny.

I'd make that saw a 390 Eddie, or as I call it mine, the little hot rod 290, no one would ever know,hehe

Great thread. Thanks for sharing.

great pics,very informative. It will help with my 029 project. Thanks.

great thread

shows just how much a working man has to go threw to fix someones dumb mistake

Great thread.. but I disagree with the flywheel removal method. yes, it's how it's taught in the silver school, but that doesn't make it right

You are applying impact force directly onto the balls/races of the bearings. Not good at all.. if you don't intend to reuse the bearings, o.k., but...

A better way (IMO) is to hold the saw by the flywheel a inch or so off the padded bench, then tap the remover (crank protector) with a small hammer. The crank is then being pushed out of the flywheel instead of being pounded into the work surface and bearings; the mass of the saw works with you.

All crank removal methods that require hitting the crank suck... some suck less.

And for all of you that think you're vindicated for hitting your cranks and using screwdrivers, this method is ONLY for the short fat taper versions as found on the likes of the stihl consumer grade saws (and the MS200/T with needle rollers) - try it on a long taper crank that requies a REAL puller, and I'll come looking for you

very informative thread Eddy, thanks for posting it. a few comments :

- I am very weary of using any torch on my workbench for repairing saws. as you correctly mentioned, fuel and fire do not really create a safe workplace. Too bad you need a special tool to remove the bar stud. Not the kinda design I like.

- the modular engine, (I have seen them on many smaller Macs), explains very well the difference between a pro and homeowner saw. You can easily understand that they save a lot on assembly cost, but there's a price to be paid for eventual service later. I'll stick with a pro saw anytime.

One question, if you do a major repair like this, do you recommend changing the crank seals or not ? I just performed a crankcase seal replacement on an Alpina 0-70, and it still has an airleak somewhere :censored: Lake will tell me I should have performed a vacuum test after case reassembly, but the seals looked good to me, so I took the risk... What do you think ?

Great thread and pics!

When you get a free moment...pm me, am curious where you are in Va.?

Nice step-by-step instructions. I think I agree with Andy on the FW removal.... I did one with the tap-off remover and it works quite well if the saw is held by the flywheel and the threaded sleeve is tapped with a small hammer (I used a plastic mallet, took two quick hits and the FW came loose) I really like the clean saw you started with, did you take it to the car wash?

Good to be back, but I sure miss rock climbing in the New River Gorge. Met an AS member there, and we got to talk saws quit a bit!

Did some concrete steps for my mother on this trip, and the TS 360 stihl works like a champ!

Back to work........vacation was much funner.

Awesome thread Eddie,,,, I have a set of Cornwall stud pullers and they pull those studs beautifully without destroying them,,,,You are right,,, a little heat works great on the rear one but I use a butane charged soldering torch while I have the stud puller camped on the stud with a 3/8 drive air ratchet just holding a little manual pressure applied, applying heat in mini burst until the stud begins to move then gas the air ratchet,,, I find the soldering torch which has a smaller diameter flame pin points the heat better!!!!

Good Idea with the heat sink metal though!!!!! I like that,,

This is a great thread,,, thanks so much!!!! for your time,,, Many can benifit from this one!!!!!

Rep incoming from tha River man!!!!! :greenchainsaw: Uhhh as soon as the system will let me,, comon guys,,, show him some Love!!!

And I use andy's method on the flywheel,,,, works every time!!!

Eddie good job!!!



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Great thread!! I wish the forum was designed so threads like this could be made into stickies and posted into a special "tech. section".

THALL10326 said:

Only thing I do alittle different is I don't heat that one bar stud up to take it out. I have the special Stihl bar stud remover socket. It goes over the stud, as you turn it it grabs the stud with tension and you can remove it without putting a mark on the threads of the stud. Sadly this specail socket costs around 50.00 but its worth every penny.

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Me too... but I use an $18 chinese SET of stud pullers. Vicegrips should be banned from all tool boxes! In any case, a stud puller doesn't have any interference from the other stud - takes seconds instead of a lot of cuss'in. And I never have to buy new studs.. The rear stud isn't cheap.


The rear stud does like heat... and the heat frees the loctite. I use a Bosch digitally controlled heat gun... best toy I bought for a long time - any temperature from 120F to 1200F in 5 degree steps (?) at any fan speed... Tom would like it 'cos it has memory - one for the Folgers warmup, one to light the cigs, one to dry the fingernail polish, and I won't even touch on the others...:greenchainsaw:

One heck of a good thread

Lakeside53 said:

Me too... but I use an $18 chinese SET of stud pullers. Vicegrips should be banned from all tool boxes! In any case, a stud puller doesn't have any interference from the other stud - takes seconds instead of a lot of cuss'in. And I never have to buy new studs.. The rear stud isn't cheap.


The rear stud does like heat... and the heat frees the loctite. I use a Bosch digitally controlled heat gun... best toy I bought for a long time - any temperature from 120F to 1200F in 5 degree steps (?) at any fan speed... Tom would like it 'cos it has memory - one for the Folgers warmup, one to light the cigs, one to dry the fingernail polish, and I won't even touch on the others...:greenchainsaw:

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Hahahha, has memory huh, may have to get me one of those if I can remember,LOL

I spoke with Eddie on the phone just a few minutes ago. He too has the stud puller like I have but he said his didn't seem to grip the stud very well, all the saws he works on his is probly wore out. Being the nice guy I am I told him I would sell him mine for a mere 100 bucks. From his reply I don't think he's gonna buy mine, I hate losing a sale. He and I must discuss this mattter further,LOLOL

Hey Tom, there is nothing left to discuss... LOL
And I agree that a good stud puller is the right tool, but the STIHL one is about $50, the Snap-On I tried was probably $100s of bucks, and I have not seen any cheap imports anywhere to try at all.
The reason I started this thread was to see what other methods are out there, but it seems the poor man method is to use heat. And I like using Vise-Grip pliers, I have several different sizes and nose configurations, and I will not get rid of them, no matter what Andy says...So There! Besides the stud is less than $5 retail, and I don't do enough of these to buy a high dollar or even medium dollar stud remover.
But I do agree with Andy that holding the saw by the flywheel and hitting the knocker is probably better, or just let the saw sit on it's base and hit sideways might be better. I always put some pressure on the back of the flywheel in some manner, such as the screwdriver, and have never had a bearing problem yet.
Belgian, it is always best practice to replace crank seals as long as you are there. Be aware on several STIHL models with engine pans, there are 2 sets of seals available. If the pan is off, you use the type that came from the factory, put a little Dirko on the outer edge and especially where the pan and cylinder mate up, as well as all the way around the pan and of course always grease the seal lips. If the pan is on there are a different set to install with a driver sleeve, and they look real different too. I will lay out the different sets and get a pic posted later.
Anyway, thanks for the comments from everyone, and eventually I will do the back together thread.

Stihl #1 said:

Hey Tom, there is nothing left to discuss... LOL
And I agree that a good stud puller is the right tool, but the STIHL one is about $50, the Snap-On I tried was probably $100s of bucks, and I have not seen any cheap imports anywhere to try at all.
The reason I started this thread was to see what other methods are out there, but it seems the poor man method is to use heat. And I like using Vise-Grip pliers, I have several different sizes and nose configurations, and I will not get rid of them, no matter what Andy says...So There! Besides the stud is less than $5 retail, and I don't do enough of these to buy a high dollar or even medium dollar stud remover.
But I do agree with Andy that holding the saw by the flywheel and hitting the knocker is probably better, or just let the saw sit on it's base and hit sideways might be better. I always put some pressure on the back of the flywheel in some manner, such as the screwdriver, and have never had a bearing problem yet.
Belgian, it is always best practice to replace crank seals as long as you are there. Be aware on several STIHL models with engine pans, there are 2 sets of seals available. If the pan is off, you use the type that came from the factory, put a little Dirko on the outer edge and especially where the pan and cylinder mate up, as well as all the way around the pan and of course always grease the seal lips. If the pan is on there are a different set to install with a driver sleeve, and they look real different too. I will lay out the different sets and get a pic posted later.
Anyway, thanks for the comments from everyone, and eventually I will do the back together thread.

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Whatcha mean there is nothing more to discuss, we haven't closed the deal yet my freind and you know me, no sale is beyond hope in my opinion. Its barter time now and I'll be fair about it and come down a tad, to oh lets say $99.99,LOLOL

Excellent thread Eddie. Many find the 290 a huzzy to work on as I did once. After doing a few they're like any other saw , just requires a bit more time and patience. When you show the pics putting it back together be sure to show the guys that ring compressor made for that saw. Many folks break rings trying to install the piston without that compressor. That handy tool is a must for the 290 family of saws.

Keep up the good work!!!

Stihl #1 said:

Anyway, thanks for the comments from everyone, and eventually I will do the back together thread.

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Right on time... I've got a ms290 to put back together soon. Waiting on the new parts now. I'm still trying to find a stud puller to get that bar stud out myself. The guy I bought the saw in a box from, looks like he tried vise grips, but he didn't mess it up too bad... No cheapie stud removers I've found. Great pics and explanations.

The saw in a box... How many parts are there on a MS290? Well, at least he put most of them in little baggies. I still have to clean them... Dirty as the day that saw got busted. I really should start taking pics of before. When you see it after I get done with it, it will be like night and day.