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Stihl 039 Rebuild

Discussion in 'Chainsaw' started by Brewz, Nov 14, 2015.

  1. Brewz

    Brewz ArboristSite Operative

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    Hi Folks.
    I bought a 2nd hand Stihl 039 about 12 months ago. It had not done a huge amount of work but had not been loved.
    When I got it the entire thing was a ball of metal, sawdust and oil under the plastic covers.
    I stripped it and cleaned it and put it back together. Modded the muffler, tuned it up, bolted on a new bar and chain and off it went.
    IMG_1280 (816 x 612).jpg
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    IMG_1283 (816 x 612).jpg
    IMG_1284 (816 x 612).jpg

    It has run fairly well but not as good as I feel it should no mater what I do.
    I have recently stripped the carb and put a kit through it, which it needed as it was full of crap and the seals were hard.
    I hadn't ventured into the motor as yet and decided to have a better look.
    I removed the muffler and shone a torch in. The top of the piston had a thick layer of black goop on it. I have used the same mix of 40:1 fully synthetic oil in 98 octane ethanol free fuel in this and my 066 and the 066 is spotless inside. Shiny silver top on the piston.
    I figure it is carbon deposited by the previous owner.

    So I popped the jug off and found a 2mm thick layer of black goop burnt onto the top of the piston and even more lining the top of the cylinder head around the spark plug.
    I also found the motor itself has a nice layer of green 2 stroke oil in it, the same as the 066 so my mix is ok.

    Inspection of the piston showed more wear on one side than the other and I found the bottom ring siezed tight on one side of the piston. Once I tapped it out I found thick layers of dry black carbon under the rings, like patched of dry tar.

    The inside of the jug cleaned up nice with a quirt of bore tech rifle barrel carbon remover. It actually looks really nice with no uneven wear or marks. There was also a 2 mm thick layer of carbon lining the exhaust port.

    I have ordered a new piston, rings, seals, bearings, hoses etc etc and will be giving it a full birthday

    I will take some pics of the gunk under the piston rings tomorrow and post em up.

    Does anyone have any advice or tips on rebuilding the motor. I am no small engine mechanic but am a tradie and very mechanically inclined.

    Cheers
     
    7sleeper, huskihl and MGoBlue like this.
  2. lambs

    lambs Stihl crazy after all these years

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    Someone will come along shortly and give you some advice, but wow, what a great looking saw! Keep us posted and good job getting it cleaned up. I am not that mechanically proficient (wish I were) but my advice is to take it slow, think it through, and you also might be able to find a shop manual available that details the steps in rebuilding.
     
  3. Brewz

    Brewz ArboristSite Operative

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    Yeah its a great saw all round!
    I love the older models as they are simple and easy to fault find. No electronic wizardry to complicate things.
    IMO machines like this should be kept simple. Fuel + Spark = bang = spin = cut firewood. Little screwdriver to tune and your good to go.

    I have dowloaded the factory parts manuals that show what goes where, but the pulling apart and bolting back together is not difficult. I spent years standing in a workshop overhauling electric motors, generators and pumps so I know how to fit a bearing properly etc etc
    Its the little tricks, or bits of info that folks that have done this before know that is the valuable information.
     
    VinceGU05 and jeff taswelder like this.
  4. MGoBlue

    MGoBlue Those who stay will be champions

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    That one cleaned up real nice! You didn't say how much you gave... indicating if it qualifies for a you suck! LOL

    When you say it doesn't run as well as you thought it should, what are you comparing it to? I was also a little disappointed with a recent 038 mag I re-did. The saw just did not impress me at all.
     
    huskihl likes this.
  5. 67L36Driver

    67L36Driver Tree Freak

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    I've overhauled eight or ten of the 029/039 Farm Boss types. The quick and easy way is to drop a Farmertec 46mm or 49mm bore complete engine in them. Cost is 60-90 bux.
    Last one I did had the crank broken on the flywheel end.
    ImageUploadedByTapatalk1447511035.304536.jpg
    Dropped in a 65cc engine.
    ImageUploadedByTapatalk1447511073.854920.jpg
    Bim bam thank you mam.
    ImageUploadedByTapatalk1447511118.074938.jpg

    Save the old top end for the next one to turn up.
     
  6. Totembear

    Totembear WoodAholic

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    They are not that hard to rebuild but those clamshells can be a pain in the butt. Got an 039 myself that a landscaper gave back to me (sold it to him) that his HELP (politcally correct) had trashed the p/c. I had a Hyway motor that I had rebuilt a while back so I was good to go. Upon further inspection found out the coil screws had backed out (messed with) and the coil had many encounters with the flywheel. Do youself a favor: pressure and vacuum test that thing as soon as you drop the motor back in. Will save you hours knowing that the engine is air tight before you move on to other things. 1 less thing to worry about if things don't turn out right. Been there done that. Also put in new seals and inspect bearings when you have it apart. Good luck, nice looking saw.
     
  7. Brewz

    Brewz ArboristSite Operative

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    Thanks so much for the replies so far folks.
    Firstly I paid $500 AU for it which is fair but no super bargain here in Australia, however good ones go for $700+
    A new MS391 retails for about $1500 AU so was worth getting and working on.

    First up, here are some pics of the piston. You can see the black carbon that had glued the bottom ring in place and the wear on one side.
    IMG_1593.jpg

    IMG_1594 (1077 x 808).jpg

    IMG_1595.jpg

    I then cleaned up the exhaust port with a file to remove all the carbon and any rough casting surface. Leveled off the muffler mounting surface as well so it will seal better. It always leaks a bit.
    Also cleaned up all the bottom end and got it all ready to be put back together.

    IMG_1597.jpg

    IMG_1596.jpg

    The crank looks good. The oil seals are hard and worn, and there was a bit of play creeping into the original bearings so they are getting replaced.
    My bearing puller is a 3 arm unit so wont work. Need to wait till the tool shops open Monday morning to get a 2 arm puller. Once they are off, its is officially fully stripped.

    IMG_1601.jpg

    IMG_1603.jpg

    The entire frame and all parts have been decreased and cleaned.
    I also found where all the oil comes from that gets it all wet and sticky. The 2 little O-Rings on the plastic connector between the oil pump outlet and where it feeds the bar are hard and flattened off, making them leak.
    Will source a couple new O-Rings to seal it back up again. I might order the factory parts through the local Stihl shop to make sure they fit properly.

    IMG_1604.jpg

    IMG_1598.jpg

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    Now to wait for all the parts to turn up on a slow boat from the USA. Its a shame express postage costs so much.
     
    7sleeper and DSS like this.
  8. Brewz

    Brewz ArboristSite Operative

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    My dad has an identical 039 that he has had since new. Its been loved and fed a good diet of good oil and fuel and maintained.
    His just seems to pull harder in the cut.
    Also, mine is far more temperamental, running great sometimes and like a pig others.
    Its why I decided to strip it and I am glad I did.

    Its also good fun to tinker in the garage at my work bench, where I can take the time to ensure the job is done perfectly.
    Music on, cold beer in hand..... It could be worse ;)
     
  9. Brewz

    Brewz ArboristSite Operative

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    Also, what is a good way to test the motor compression when I am done without having to buy expensive test equipment.
    I won't be doing this sort of work often.

    Edit: Youtube :rock2:

    I found a fitting same thread as the spark plug and will track down a 200psi gauge tomorrow
    Should get me out of trouble.
     
  10. anlrolfe

    anlrolfe Honor GOD, Country and Corps

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    Just run it. When you get the new piston and rings in the old cylinder it will take them a bit to settle in. There's not much you can do about it either. Can't play with gasket delete. Squish is fixed. No sense worrying about something you can't change. Just run it.

    About the carbon build up, rebuilding the carb and changing to a quality mix oil will probably do wonder. Get 'er tuned up well and run 'er mate.

    btw, looks like you've got a handle on the rebuild.
     
  11. Brewz

    Brewz ArboristSite Operative

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    Yeah I have no plans to modify it other than a muffler mod. I just want it all running reliably with loads of compression and no oil leaks.
    I am really pleased with how it has come apart and cleaned up.

    When I get it back together, what is the best way to run it in to ensure it stays happy. I don't want to just rev the guts out of it in some hardwood and damage it again.
     
  12. Totembear

    Totembear WoodAholic

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    Yeah, looks like you have a good idea of where your going with this rebuild. I would still p/v test it before putting flywheel, clutch, handle on it. If you dont have access to a p/v tester just make sure your seals are good. I always use Stihl, aftermarket can be hit or miss IMO. Always put a really thin coat of sealant around the seals, just for good measure. Send pics as soon as you are done!
     
  13. Totembear

    Totembear WoodAholic

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    As far as running it, just make sure the fuel mixture is right and its oiling right. Make sure its 4 stroking and in the cut it cleans up and doesn't bog down. Might take a few cuts to get it right. Make sure you clean the air filter too as this can help prolong its life. Other than that, enjoy the fruits of your labor!!
     
    jeff taswelder and anlrolfe like this.
  14. lambs

    lambs Stihl crazy after all these years

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    The 039 was my go to saw before I found my 046. It's a good idea to clean your air filter with compressed air after each use. You may never wear it out!
     
  15. Brewz

    Brewz ArboristSite Operative

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    I replaced the air filter when I got the saw and keep it clean
    I blow it out gently from the inside and then wash in warm soapy water.
    Keeps it like new
     
  16. fearofpavement

    fearofpavement Trying them all

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    That piston is probably still serviceable. Don't toss it.
    As far as the muff mod, I've found about 1.25 open on the H and 1.0 on the L will put you in the ball park. Here's the mod I've finally settled on after trying a number of variations on different saws of this series.
    Make sure you get all the chips/shavings out of the muffler before installing.

    upload_2015-11-15_21-15-35.jpeg
     
  17. Brewz

    Brewz ArboristSite Operative

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    I have done this:

    039 muffler mod new 1.jpg

    I angled the holes to direct the gas towards the exit in the front cover.
    I also enlarged the hole in the exit from the little square one it was originally.
    I still want to make this bigger, and will do before it goes back together.
    I also have some fine SS mesh with more open area than the factory mesh..... up around the 56% open area mark. I would put the factory mesh at 40% open if its lucky. It is definitely darker to look through.

    039 muffler mod new 4.jpg

    I ordered the O-rings for the bar oil system today through Stihl and have a bearing puller on the way so I can finish stripping the crank.

    I really cant wait to get this baby back together and fire it up. I'm all excited :crazy2:
     
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  18. Brewz

    Brewz ArboristSite Operative

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    My bearing puller turned up yesterday so I have now removed the old bearings and cleaned up the crank. Its in very good condition!

    IMG_1617 (1077 x 808).jpg

    I also replaced the oil pump connector o-rings. For anyone interested they are a Stihl 4 x 1.5mm o-ring. It now fits on tightly and should stop the leaking oil making the saw an oily sawdust coated mess.

    IMG_1616 (1077 x 808).jpg

    IMG_1615 (1077 x 808).jpg

    Now I just need to wait for a box to turn up full of new bits to install.
    One other thing I have chased up is a tube of gasket goo
    I was recommended this stuff below. Anyone have any experience with it?

    IMG_1618 (450 x 600).jpg
     
  19. fearofpavement

    fearofpavement Trying them all

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    I wouldn't use any type of rtv on a chainsaw. Some do and claim good results but you should use a sealer designed for continuous fuel contact which is what you'll have. There's lots of posts regarding good sealers. I personally use Motoseal 1. (a Permatex product)

    On the crank bearings, I lay them on a piece of wood and heat them up with a heat gun. They will easily slide onto the crank. Hold that end of the crank up until the bearing cools a bit. Then do the opposite side.

    Cutting a hole in thin sheet metal on an angle will not redirect the flow of exhaust gas. Won't hurt anything, just doesn't accomplish anything for the additional effort. Your muffler mod looks fine.
     
    Brewz likes this.
  20. Brewz

    Brewz ArboristSite Operative

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    Thanks for the advice fop
    I will shelve the Permatex Black and have contacted a local Permatex distributor to have some Motoseal 1 ordered in as no-one carries it on the shelf.
    It is the stuff Permatex recommend for 2 and 4 stroke engines.

    Bearings wont be an issue, I worked for years overhauling electric motors from the size of your fist to the size of a truck. Have fitted one or 2 over the years.
    Never re-built a petrol motor though, and its bits of advice like yours above that was the motivation for starting this thread.

    Thanks!
     
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