# Stihl ms 290 chainsaw rebuild



## ccrider966 (Jul 8, 2006)

I got the engine out and am getting ready to rebuild with a new cylinder and piston assy I plan to get from Ebay. I am concerned about the 4 engine mounting self tapping screws and how to reinstall. I don't see how the engine can be inserted into the housing without the crank case separating, especially if I have to hold it in place while screwing the self tapping screws in. I had a lot of difficulty getting the engine out of the housing since it was such a tight fit! This is further complicated since the 2 halves of the engine must be sealed with silicone and the crank seals held in place.
Naturally I destroyed the other engine mounting bolt that doubles as a blade mounting bolt. I tried to double nut it but could not get it out that way as suggested here. I will get a new one and it does not look like a self tapping bolt.
I will post other questions here as I get started and hope someone with experience with these saws will bear with me!


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## paulr44 (Oct 14, 2008)

The MS290 and other saws Stihl makes that have plastic based lower crankcase halves, are a PITA to rebuild. The flat rate for a cylinder replacement is like 2 hrs. for an experienced tech WITH clean components, so being unfamiliar will obviously add to that time, as well as cleaning. Flat rates are often averages, so you decide...

Anyway, you'll have to clean all of the sealant from the mounting flanges, and you MUST, ABSOLUTELY MUST use a high-end sealant such as what Stihl sells, Dirko. OR, some other ANAEROBIC, FUEL-IMPERVIOUS sealant ELSE the seal may fail and the saw will probably toast itself running lean from a vacuum leak. REGULAR RTV sealant that costs like $4 a tube IS INSUFFICIENT and inferior for the task at hand.

Any engine that splits at the crank centerline is going to be a bit of a challenge to assemble. You have to compress the rings and get them into the cylinder, while trying not to get the pre-applied sealant over everything.

We usually condemn any of this type of saw needing a cylinder, as it's just too much work and expensive. The MS290, while supplies last (is being phased out) is $399. It's replacement, the MS291 is $100 more.

*I don't understand what you mean by blade mounting bolt...could you mean bar-stud?*

To be honest, even though I've worked on Stihl products for 30 years, I probably have only rebuilt 1 center-line split crankcase saw, and maybe a handful of other units like trimmers or blowers that also split center-line. I am very familiar with the 290 in all other regards though...will try to help but am quite busy myself so if I don't answer right away have some patience.

Paul


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## paulr44 (Oct 14, 2008)

Send me an message with a regular email address in it. I have a manual that'll help you.


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## ccrider966 (Jul 8, 2006)

Hi...I am [email protected]. I have a cd that shows the stihl ms 290 repair manual. I have studied it and will proceed cautiously! The parts arrived today. I need to get the special crankcase sealant next.


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## ccrider966 (Jul 8, 2006)

I have the new cylinder and piston now. I need to get the special crankcase sealant next. I hope I can get the rings on the piston and get the piston in the cylinder ok. Sounds like you put the sealant on before putting the piston in the cylinder, I was hoping to add the sealant later but never looked at it to see if that can be done. I think the rings are positioned with stops to locate them properly. How about the piston? The repair manual shows an arrow on the top to line it up correctly. I have not actually got the piston and cylinder to the house yet since it was raining so hard the post office delivery van did not leave it at the mail box. I do not have a ring compressor either, so I hope I can shove it in ok.
I sure appreciate getting help from you professionals here on this site!


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## ccrider966 (Jul 8, 2006)

Yes, I meant the bar stud. I tore up the original removing it and have got replacement now. I have some loctite but do not know if it is the correct one to use. I guess you double nut the stud and torque it in place using the nuts.


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## ccrider966 (Jul 8, 2006)

I now have all the parts I need except the special sealant. When I looked at the technical data sheets for Dirkco, Permatex Ultra Black or Grey, etc. all of them say they are not gasoline resistant! I am beginning to think the Permatex versions are the same thing only a lot cheaper than the Dirco specified by Stihl in my workshop instructions. Surely Permatex has a product for this type application.
Also I put the rings on the new piston and it seems near impossible to get it into the bore without a ring compressor. Also I wonder if it would not be a good idea to put the piston in the bore and then add the sealant and finally fit the wrist pin to connect the crankshaft, bearings, seals, etc. I can see it might take a bit of doing to get the piston and rings into the bore and the sealant would be in the way more with the crankshaft attached.


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## paulr44 (Oct 14, 2008)

1. The piston rings have locator pins to align with in the piston. You won't be able to get the cylinder on without the rings aligned, else you'd have to force it which would break a ring or both.
2. To apply the sealant after getting the cylinder onto the piston would probably result in less sealant mess, but I don't see how you could apply it effectively and evenly.
3. I was going to send you the manual, but you state you already have it.
4. The bar stud...double nutting it is the most common method.
5. The ring compressor Stihl sells is just a plastic band with finger stops, works well and is very cheap, P/N 0000 893 2600. On standard style 2-strokes (where cylinder comes off but crankcase doesn't split at crank centerline), another Stihl tool that's cheap and effective is the piston block, which you'd put under the piston skirt to assist in installing the cylinder onto the piston. It's just a small piece of wood with a dado cut down most of it's length, P/N 1108 893 4800. For how cheap they are, I don't even try to make 'em.


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## ccrider966 (Jul 8, 2006)

I looked at fitting the piston alone first but found the wrist pin could not be inserted that way. So I got the rings on the piston and fitted the wrist pin to it and the crank rod with the clips positioned so their gap is aligned with the vertical axis as shown in the manual. I think I can get the piston and crank assembly in the cylinder without a ring compressor and I see you are right, the rings will not allow installation if they are not aligned with the location pins.
All I am waiting for now is the sealant for the case. I have read all the tech data sheets of lots of sealants. The only ones I found that claim gasoline resistance is the anaerobic flange sealants that are really expensive. Even the Dirko called for in my shop manual said it was not meant for gasoline! I found one from Permatex that claims it is meant for gasoline and even mentions use in sealing crankcase halves. It is Permatex Moto-1 Ultra Grey I think I will try that. It claims temperature of 350 F continuous duty is ok.


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## jsouth (Jan 31, 2008)

Type in donyboy73 on youtube,and watch the 4 part series on rebuilding a stihl chainsaw,it is very useful. T he chainsaw is a ms250 that he is rebuilding.At the top of is channel is a search box just type in stihl chainsaw ms250. I know yours is a ms290.this may help.

Jerry


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## paulr44 (Oct 14, 2008)

BTW the arrow on 2-strokes always points toward the exhaust port. At least, on all the many I've worked with. Stihl usually puts 1 wrist pin circlip in for you. Can't speak for the MS290 piston, but the circlip they put on the one's I've rebuilt is on the clutch side, as there's more access room on the flywheel side so it's easier to install that clip second. Since the 290 splits at CC centerline and you'll be putting the piston on with the crankshaft alone on the bench, it doesn't matter which one you do first.


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## ccrider966 (Jul 8, 2006)

Thanks, I did look at the youtube rebuild and it is helpful even if it is not a 290. I wish Paul would do one for the 290 to help other guys!
I got the piston arrow pointing to the exhaust port or front of the engine and found the original problem with my saw! One of the circlips for the wrist pin had its "tail" broken off and was likely the cause of the piston/cylinder damage to my saw! I could not find the "tail" inside the saw and assume it finally made it out the exhaust port!
I am surprised the manual cautions putting the circlip "gap" on the vertical axis of the piston. I guess that the inertia forces from such high rpm might cause some sort of fatigue on this part if placed horizontal.
My only remaining problem is the sealant where I found so much conflicting advice on the net and is very critical. Once I get it, I will try to fit the piston assembly into the cylinder without a ring compressor. Then I should be able to lift the crank up slightly and apply sealant to the cylinder half and the seals. The bottom half would be no problem then to apply the sealant and fit it on. The trick then is to get the engine inside the case and start the mounting bolts without moving anything.
I am glad you are following this thread and I am sure others will benefit from your professional advice! If this thing ever runs I will feel a great sense of accomplishment! So far I have less than $100 in parts from Ebay and the saw was only $25 at a garage sale. I have 2 others like it that I have used for years and love............


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## ccrider966 (Jul 8, 2006)

By the way, the manual says to put the "sealing ring" of the seal toward the outside. My original seals were installed with the "open end" of the seals to the inside and the new seals have the conventional "garter spring" on the lip on the open side, and I plan to put that toward the inside. I wonder if the "sealing ring" in the manual refers to the metal ring molded inside the seal and not the "garter spring". 
I am sure the open end of the seal goes to the inside, right?


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## paulr44 (Oct 14, 2008)

On split CC engines, Stihl usually has 2 types of seals available...one for replacement with the engine intact, the other for if you have the CC split. They look different, and perhaps are slightly a different O.D. but never measured them to see.


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## ccrider966 (Jul 8, 2006)

Great news, I got it together and it runs! I broke down and bought the $16 Dirko as Paul suggested. The piston went in easily once oiled up which I was worried about. The aftermarket cylinder and piston for $42 on Ebay seems to work fine. Time will tell though. It took me 4 hours yesterday but I could do it a lot faster now. I have 3 of these saws and will be looking for others that I find at garage sales, etc. to rebuild. I really like them. I think the piston in this one failed because a small piece of the wrist pin wire clip broke off and jammed the cylinder. I never found the piece but hope it went out the exhaust! 
I want to thank those on this board who helped and hope others will find this thread helpful to them as well..................


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## Don L (Jul 14, 2012)

If you like the 290 you'll love the 310 and 390.Basically the same saw,just bigger piston and cylinder which equals more power at the same weight.They also run the 3/8 chain instead of the .325 pitch as on the 290.
The 390 was even equipped with a compression release.
Happy to hear it worked out well,I will definetely look into rebuilding some of my old parts saws at prices like those.Thanks for posting the info.
Don:wave:


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## paulr44 (Oct 14, 2008)

Excellent. I'm glad, and you will be too that you bought the high-end sealant. Having done any number of engine rebuilds, that's one thing you can't play games with. Got my hands busy right now rebuilding several larger saws, so can't say I'll be able to be here much.
Good luck!


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