Stihl 039 Chainsaw Rebuild

[BigBrian]

Good morning all!

Today I will be cutting down a few smaller trees on my property. When I went to grab my medium sized saw to fuel it up and make sure it is ready to go, I saw my old Stihl 039 that I got given to me for free from a buddy. It has a seized cylinder from when someone ran straight gas. I received it partially disassembled, with the removed parts in a bag tied to the saw. It did not come with a bar although I have several spares.

Now that my project motorcycle is finished, i'd like to try my hand at repairing this saw. I have never gone that deep into a chainsaw before but it seems fairly straightforward. I have a garage full of tools, an open mind and a willing attitude.

Never having done this before, I assume I will need a new cylinder, piston & rings. Possibly the crank as well? Where are the best places to purchase these parts? If I could buy a complete rebuild kit with everything I need, I'd rather go that way.

Thank you!

 

[Davefr]

This is not a good candidate for your first chainsaw rebuild. This series of saw had the dreaded clamshell style cylinder. (as opposed to professional grade saws where you could easily replace just the top end.)

I suggest you watch this video just to get a feel of what's involved. (same family of saw)

Your choice of parts will be OEM (spendy) or aftermarket (iffy). Pick your poison.

Good luck.

 

[308guru]

The cost of Stihl parts will blow your mind when you look. There are kits by Meteor or Cross Performance that will net you a good running saw again if you care to save some coin.

 

[B_Bimmer]

I rebuilt one of those in a similar situation with a cheap chinese kit off ebay. I had low expectations but have put fourty gallons on mix through it over the last four years and it runs strong.

 

[classic70]

How much are you wanting to invest? You could end up putting 300 plus in the saw if you bought stihl parts. Aftermarket parts are super cheap for that saw. I would pressure/vac test the saw before tearing it apart to make sure crank seals are good. If crank seals are good, you could put a AM piston and cylinder kit in for less than 100 bucks. These saws are kind of a pain to work on compared to other saws but if you are mechanically inclined should be no issue for you to rebuild. T27 torx bit and a few sockets is all the tools you should need.

 

[Firebrick43]

Get it apart first. Many times you can save the cylinder with Muriatic acid (concrete etch) applied carefully with a q tip to de solve the aluminum transferred from the piston to the nickisil coating stihl uses.

I, and many others have used Meteor for pistons with good results.

Unless the saw was just beat and wore out before it was straight gassed it’s not that common to have crank damage.

 

[finn]

Plan on replacing the crank seals. Unless you’re absolutely sure it is the victim of straight gas, it could be bad crank seals or a worn throttle shaft that leaned out the mixture and caused the scoring.

I have seen both.

The 039, although not as easy to rebuild, is still worth rebuilding unless it’s spent the last twenty years in a pond.

They’re pretty sound firewood saws, and if this is your first saw, you don’t need a pro grade saw.

 

[freudianfloyd]

Good morning all!

Today I will be cutting down a few smaller trees on my property. When I went to grab my medium sized saw to fuel it up and make sure it is ready to go, I saw my old Stihl 039 that I got given to me for free from a buddy. It has a seized cylinder from when someone ran straight gas. I received it partially disassembled, with the removed parts in a bag tied to the saw. It did not come with a bar although I have several spares.

Now that my project motorcycle is finished, i'd like to try my hand at repairing this saw. I have never gone that deep into a chainsaw before but it seems fairly straightforward. I have a garage full of tools, an open mind and a willing attitude.

Never having done this before, I assume I will need a new cylinder, piston & rings. Possibly the crank as well? Where are the best places to purchase these parts? If I could buy a complete rebuild kit with everything I need, I'd rather go that way.

Thank you!

The Farm Boss series of saws are easy to rebuild and parts are plentiful if you are ok with going after market. You may also get lucky and be able to clean up the cylinder and get by with just a new piston and rings. Typically when a saw is straight gassed, which that one appears to have had happen judging by the picture where the piston is visible through the exhaust port, you can use muriatic acid to remove the aluminum transfer that is sticking to the cylinder walls. A ball hone with lots of oil after to refinish. I have done this several times with good results.

***I see a few others mentioned the same as myself so sorry to repeat the same thing again.

 

[Packard V8]

FWIW, I attended an introduction when that series of saws came out. After the formal presentation, over a beer, a factory engineer said those saws were built with the idea they'd never get any maintenance in their lifetime and would be throwaways rather than rebuilders.

When I said I was shocked Stihl was cheaping out, he said, "That's the US market for you. Much more profitable to sell more for cheap than fewer gooder."

jack vines

 

[BigBrian]

Thanks everyone!

I am going to try my hand at rebuilding this saw. It cost me $0 so I don't have a whole lot to lose. Worst case, I learned some knowledge and spent a little money (not going Stihl parts because $$$).

I was extremely busy today, all I was able to do is confirm that the saw is not locked up like I previously thought. I was able to get the piston to move with little effort from the pull starter. It is obviously in poor shape from all the scoring you can see on the piston skirt.

I'll pull it apart this week if I have time and keep you all updated.

Thanks again!

 

[BigBrian]

Well I was able to get everything torn down & inspected soon than expected.

This saw wasn't difficult to take apart. The biggest struggle I had was removing the stud that bolts to the engine through the frame.

It looks like someone had been in the saw before, there's lots of blue rtv that was used to seal the 2 halves of the engine.

Ok now on to the bad...

Piston is shot, obviously I knew that already. The cylinder walls are scored on the exhaust side only. I did the muriatic acid & q-tip trick, that's pretty neat!! However, I can still feel a deep gouge in the wall, not sure it's worth trying to hone.

The crankshaft bearings were no good. One side is completely missing the cage and the other feels rough. Fortunately I work for an industrial supply company and we stock the replacements. The oil seals are also hard as a rock since they're so old. I suspect Stihl makes them an odd size (17mm x 30mm × 4.4mm) so you can't just go down to any parts store and get them. I'm going to check with my suppliers at work tomorrow and see if they have them.

I'll also need to replace the fuel line and a small line that has a brass "screw" inside. Not sure what that is...

Despite a portion of the saw being in parts in a bag, im only missing 1 T27 torx screw & muffler bolt.

After all was torn apart, I took the parts to my parts washer and scrubbed them really well. They were filthy and no one likes working on dirty equipment.

So that brings us to now, I'm debating on what to do. Do I try & hone the Stihl cylinder or just get a new one?

 

[NUTTSGT]

Interesting. I still have an 046 that I bought a big bore kit for and it's just sitting on a shelf. I bought most of my stuff from Saw Again.com as they had decent prices at the time.

 

[Rich.Wolfson]

Well I was able to get everything torn down & inspected soon than expected.

This saw wasn't difficult to take apart. The biggest struggle I had was removing the stud that bolts to the engine through the frame.

It looks like someone had been in the saw before, there's lots of blue rtv that was used to seal the 2 halves of the engine.

Ok now on to the bad...

Piston is shot, obviously I knew that already. The cylinder walls are scored on the exhaust side only. I did the muriatic acid & q-tip trick, that's pretty neat!! However, I can still feel a deep gouge in the wall, not sure it's worth trying to hone.

The crankshaft bearings were no good. One side is completely missing the cage and the other feels rough. Fortunately I work for an industrial supply company and we stock the replacements. The oil seals are also hard as a rock since they're so old. I suspect Stihl makes them an odd size (17mm x 30mm × 4.4mm) so you can't just go down to any parts store and get them. I'm going to check with my suppliers at work tomorrow and see if they have them.

I'll also need to replace the fuel line and a small line that has a brass "screw" inside. Not sure what that is...

Despite a portion of the saw being in parts in a bag, im only missing 1 T27 torx screw & muffler bolt.

After all was torn apart, I took the parts to my parts washer and scrubbed them really well. They were filthy and no one likes working on dirty equipment.

So that brings us to now, I'm debating on what to do. Do I try & hone the Stihl cylinder or just get a new one?

Bring that cylinder to a Kart shop and they will fix it right up. ///Rich

 

[Firebrick43]

Well I was able to get everything torn down & inspected soon than expected.

This saw wasn't difficult to take apart. The biggest struggle I had was removing the stud that bolts to the engine through the frame.

It looks like someone had been in the saw before, there's lots of blue rtv that was used to seal the 2 halves of the engine.

Ok now on to the bad...

Piston is shot, obviously I knew that already. The cylinder walls are scored on the exhaust side only. I did the muriatic acid & q-tip trick, that's pretty neat!! However, I can still feel a deep gouge in the wall, not sure it's worth trying to hone.

The crankshaft bearings were no good. One side is completely missing the cage and the other feels rough. Fortunately I work for an industrial supply company and we stock the replacements. The oil seals are also hard as a rock since they're so old. I suspect Stihl makes them an odd size (17mm x 30mm × 4.4mm) so you can't just go down to any parts store and get them. I'm going to check with my suppliers at work tomorrow and see if they have them.

I'll also need to replace the fuel line and a small line that has a brass "screw" inside. Not sure what that is...

Despite a portion of the saw being in parts in a bag, im only missing 1 T27 torx screw & muffler bolt.

After all was torn apart, I took the parts to my parts washer and scrubbed them really well. They were filthy and no one likes working on dirty equipment.

So that brings us to now, I'm debating on what to do. Do I try & hone the Stihl cylinder or just get a new one?

If the nickasil coating is scratched there is little chance of saving it and it’s not economical enough to pay the people who can possibly fix it.

An Italian made meteor kit with cylinder and piston/rings is only 135$~

 

[BigBrian]

If the nickasil coating is scratched there is little chance of saving it and it’s not economical enough to pay the people who can possibly fix it.

An Italian made meteor kit with cylinder and piston/rings is only 135$~

It's more than scratched, it's gouged. I can catch the gouge with my fingernail. It's done.

I'm having trouble finding a meteor kit in stock, the Hyway kit is around $99. I know its Chinese but appears to have decent reviews.

 

[Lasu]

I would remove most of the aluminum from the cylinder walls with sanding pads, cloths/paper + maybe a new piston.

 

[F-22]

Meteor is high quality, I'd suggest you get that and a new crank. Those saws are certainly worth it. I have the exact same one. As you already took it apart, you probably have your own opinion about it - but I think they are quite simple and straightforward to take apart. Yes the "pro" models are even easier but for a homeowner saw this is more than fine.

 

[BigBrian]

I would remove most of the aluminum from the cylinder walls with sanding pads, cloths/paper + maybe a new piston.

I dissolved it all with muriatic acid, it's scored badly

Meteor is high quality, I'd suggest you get that and a new crank. Those saws are certainly worth it. I have the exact same one. As you already took it apart, you probably have your own opinion about it - but I think they are quite simple and straightforward to take apart. Yes the "pro" models are even easier but for a homeowner saw this is more than fine.

I must admit, the saw was user-friendly as far as disassembly goes. Absolutely worth putting money into it especially considering I got it for free.

Out of curiosity, why would you also replace the crank? The big end bearing did not have any up and down play and I can replace the 2 support roller bearing for cheap.

 

[NUTTSGT]

It's more than scratched, it's gouged. I can catch the gouge with my fingernail. It's done.

I'm having trouble finding a meteor kit in stock, the Hyway kit is around $99. I know its Chinese but appears to have decent reviews.

Yep, looking like it's sold out. Probably more people rebuilding right now than buying new.

 

[M635_Guy]

I love threads like this & glad it won't just end up in a landfill.

Will be interested to see it getting put back together!

 

[cgrutt]

Meteor Nikasil cylinder piston kit for Stihl MS390 039 MS310 MS290 029 49mm - Wolf Creek Saw Shop

Brand new Meteor 49mm cylinder/piston kit. Fits Stihl chainsaw model MS390

www.wolfcreeksawshop.com

Says 2 kits in stock. There is a discount code at top of page. No experience with these kits or vendor just passing along.

 

[BigBrian]

I love threads like this & glad it won't just end up in a landfill.

Will be interested to see it getting put back together!

I love watching others save stuff as well so I figured it was my turn!

Meteor Nikasil cylinder piston kit for Stihl MS390 039 MS310 MS290 029 49mm - Wolf Creek Saw Shop

Brand new Meteor 49mm cylinder/piston kit. Fits Stihl chainsaw model MS390

www.wolfcreeksawshop.com

Says 2 kits in stock. There is a discount code at top of page. No experience with these kits or vendor just passing along.

Now there's only 1 left!

 

[BigBrian]

Now that the majority of parts are ordered, I stihl (ha-ha) need a few other odds & ends that I'll be ordering from my local Stihl dealer today.

I need;

Muffler bolt (I'm missing one)
Fuel line (mine is ripped)
Oil seals (hard as a rock)
T27 torx screw (missing one)
Tank breather (ripped)
Muffler gasket (wear item)
Wrist pin bearing (wear item)
Air filter (wear item)
Yamabond (to seal the chamber to cylinder)

 

[Davefr]

Now that the majority of parts are ordered, I stihl (ha-ha) need a few other odds & ends that I'll be ordering from my local Stihl dealer today.

I need;

Muffler bolt (I'm missing one)
Fuel line (mine is ripped)
Oil seals (hard as a rock)
T27 torx screw (missing one)
Tank breather (ripped)
Muffler gasket (wear item)
Wrist pin bearing (wear item)
Air filter (wear item)
Yamabond (to seal the chamber to cylinder)

Do you have the Stihl 039 OEM workshop manual and parts list? If not, go to the "beg for manuals" thread at arboristsite.com. (they've never let me down when I need factory manuals)

 

[BigBrian]

Do you have the Stihl 039 OEM workshop manual and parts list? If not, go to the "beg for manuals" thread at arboristsite.com. (they've never let me down when I need factory manuals)

I was able to find and download a parts diagram & saw manual, but I appreciate the tip.

I also ordered the parts I needed from the Stihl dealer along with a new chain & bar, I went with a 20" setup.

Speaking with my buddy who gave me the saw, I was under the impression that he had purchased the saw new and lent it to a neighbor who straight gassed it but apparently it was his neighbors saw and the neighbor gave it to him after he (the neighbor) accidentally straight gassed it. I'm glad it will get to live again.

 

[F-22]

Out of curiosity, why would you also replace the crank? The big end bearing did not have any up and down play and I can replace the 2 support roller bearing for cheap.

Would probably just swap the side bearings then, the crank is likely pricey?

 

[BigBrian]

Would probably just swap the side bearings then, the crank is likely pricey?

That's the plan. I'm going to put the new bearings on today after work.

 

[BigBrian]

New bearings are installed, put crank in freezer and heated bearings with a heat gun and they just about fell onto the crank.

New piston kit is in as well. I'm still waiting for the wrist pin bearing to assemble everything but I did install the rings on the piston and 1 circlip. I made sure to check the ring gap first. Put 1 ring in at a time and squared it with the piston then used my feeler gauge to measure the gap. At 49cc, the manufacturer says I should have .004" per 1 inch of bore, that means the gap should be .077" I was able to get a .008" feeler gauge in albeit slightly tight. Should be right on the money.

I'm using Stihl 2 stroke mix as my assembly lube, was always told the best assembly lube is the same that will be running through that area once it's all completed i.e. brake fluid for caliper rebuilds, etc.

I cleaned the carb as well, didn't look dirty but a dunk in the sonic cleaner won't hurt, just used a mix of hot water & dawn dish soap.

As far as what to use for the gasket material to seal the cylinder, I have a tube of Hondabond 4 in my toolbox, that will work just fine and certainly better than the blue RTV someone else used.

Speaking of blue RTV, I have a feeling someone was in the saw before me, the blue RTV is suspicious. No way Stihl used that from factory. Also, I believe I found the real reason the saw died. I think there was an air leak at the base. The symptoms of that, (at least from what I have been reading) are usually exhaust side scoring and that is exactly what I found when I pulled this saw apart. Plus the blue RTV that was used as a base sealant is not to be used for things in contact with gasoline as it is soluble in gasoline.

Anyway... just ranting waiting for my local ACE to get my wrist pin bearing in stock so I can finally put this 'ol girl back together.


ALSO! If anyone has any tips to installing the piston that would be great! I don't have a piston ring compressor that goes that small, I was just going to use patience and my fingers... (easy boys!)

 

[mike93lx]

ALSO! If anyone has any tips to installing the piston that would be great! I don't have a piston ring compressor that goes that small, I was just going to use patience and my fingers... (easy boys!

Hose clamp and some aluminum from a soda can?

 

[BigBrian]

Hose clamp and some aluminum from a soda can?

I just found & purchased a $10 piston ring compressor set for small engines.

 

[Rinspeed]

New bearings are installed, put crank in freezer and heated bearings with a heat gun and they just about fell onto the crank.




ALSO! If anyone has any tips to installing the piston that would be great! I don't have a piston ring compressor that goes that small, I was just going to use patience and my fingers... (easy boys!)

I've found it easier to just use your thumbs to compress the rings while someone else helps guide the piston in.

 

[cgrutt]

New bearings are installed, put crank in freezer and heated bearings with a heat gun and they just about fell onto the crank.

I'm actually surprised that worked aren't you supposed to freeze the bearings (cold contracts) and heat the crank (heat expands)? Anyway congrats.

 

[BigBrian]

I'm actually surprised that worked aren't you supposed to freeze the bearings (cold contracts) and heat the crank (heat expands)? Anyway congrats.

In a normal setup you'd be 100% correct but this is the clamshell style cylinder where the bearings are pressed onto the crank and are clamped in the cylinder by the 4 bolts through the engine.

Look at my disassembly pic, it will make more sense.

 

[cgrutt]

In a normal setup you'd be 100% correct but this is the clamshell style cylinder where the bearings are pressed onto the crank and are clamped in the cylinder by the 4 bolts through the engine.

Look at my disassembly pic, it will make more sense.

Oh gotcha my apologies. I rebuilt my son's dirtbike and bearing dropped into the case i was thinking it was like that. My bad.

 

[BigBrian]

Oh gotcha my apologies. I rebuilt my son's dirtbike and bearing dropped into the case i was thinking it was like that. My bad.

No worries!

 

[BigBrian]

Still waiting for my local ACE to get the rest of my parts in. They said the parts would be in sometime this week thankfully.

 

[BigBrian]

Still no parts, and I have a week of sales meetings coming up so I won't have time to work on the saw even if I had the parts... sigh...

 

[Snapped-off]

Surprised @bulletpruf hasn't popped in.

 

[bulletpruf]

Surprised @bulletpruf hasn't popped in.

Thanks for the heads-up.

Lots of good info here, and sounds like you're on the right track.

I also use 2 stroke oil as assembly lube, but don't go overboard and/or drain the excess out of the crankcase once it's together or it won't be very easy to start at first.

I would definitely rebuild the carb. Easy enough to do and now is the time to do it.

It will also be well worth your time to do a muffler mod. I've never built an 039, but I generally disassemble the muffler and drill out or remove the baffle and add an exhaust port. Lots of YouTube videos on how to do this.

Are you doing a base gasket delete and using Yamabond instead of base gasket? If so, might be worth your while to check piston to jug clearance - I use soldering wire held on to the top of the piston with a dab of grease in 4 different places. I typically do a base gasket delete on all the saws that I rebuild, but on some, you don't have enough clearance so I either use a factory gasket or make a custom one with thinner material.

Edit - a 20" bar is about right for that saw, but it should be able to handle up to 24", especially in soft wood. You're going to run 3/8" chain, right?

 

[BigBrian]

Thanks for the heads-up.

Lots of good info here, and sounds like you're on the right track.

I also use 2 stroke oil as assembly lube, but don't go overboard and/or drain the excess out of the crankcase once it's together or it won't be very easy to start at first.

I would definitely rebuild the carb. Easy enough to do and now is the time to do it.

It will also be well worth your time to do a muffler mod. I've never built an 039, but I generally disassemble the muffler and drill out or remove the baffle and add an exhaust port. Lots of YouTube videos on how to do this.

Are you doing a base gasket delete and using Yamabond instead of base gasket? If so, might be worth your while to check piston to jug clearance - I use soldering wire held on to the top of the piston with a dab of grease in 4 different places. I typically do a base gasket delete on all the saws that I rebuild, but on some, you don't have enough clearance so I either use a factory gasket or make a custom one with thinner material.

Edit - a 20" bar is about right for that saw, but it should be able to handle up to 24", especially in soft wood. You're going to run 3/8" chain, right?

I appreciate all the information!

As far as the 2 stroke oil as assembly lube goes, I am not planning on using a ton, just enough to get everything coated and slippery, certainly not enough to pool in the lower end.

I actually did pull the carb apart and give it a dunk in my sonic cleaner to make sure there was no debris or obstructions in any of the passageways.

I thought about doing a muffler mod, but I was a bit hesitant due to the fact that I don't have a lot of experience tuning carbs on small 2 stroke engines. I've tuned my other saws before so I have some experience and the tools required (carb screwdriver set, tach, etc). Maybe I will look into this.

From looking at the Stihl parts diagrams online, it appears that there is no base gasket. Stihl lists a tube of sealant as what is used to seal the 2 halves instead of a gasket so I think I will be ok. Also, when I took the saw apart, there was blue RTV instead of a gasket and I didn't see any issues with clearance, but I appreciate the warning.

I am planning on running the 20" bar as I have a Stihl 056AV for larger trees and I find that the 20" bar is a perfect size for 90% of what I do. I will be running a 3/8" chain as that's what my clutch is setup for already.