Still 039

[jerkputter123]

My cousin has an older Stihl 039 chainsaw ser # 231608771 that burned up the cylinder and piston , maybe more.

The oil mix was correct according to him. He bought this saw new but let his grandson use it to cut firewood. He left mixed gas with it when he loaned it out. Grandson used the gas granddad brought and this gas mix has been used in his other saw and no issues.

Now the problem is would this 039 be worth replacing the cylinder and piston or get a rebuilt unit off ebay ? I told him I would think long before I ordered just a cylinder and piston. I viewed this chainsaw yesterday and it is indeed toast. Anyone had any luck buying a compete engine assembly ? Suggestions welcomed.

[bgsengine]

can usually fine a jug & piston kit on ebay in aftermarket offerings that would rebuild the saw pretty well - in my experience they are no worse than original Stihl parts any more.. However, just gonna have the same problem again if the root cause is not found - doesnt necessarily have to be the gas mix causing the issue - there's other maintenance items that can cause lean condition or overheating (2 most common things causing engine failure) so, you'd need to actually diagnose thee root cause of the failure so it can be corrected while the saw is being fixed to begin with.

[jerkputter123]

Thanks. I will pass that on to him. I had actually mentioned that to him before . You think it would be best to just get the complete engine or just cylinder and piston? He said the crank seems to be ok but I have not checked it for him. I found a NEW Complete Assembled Engine for around $100. I would think that would be the way to go being this would be nice a sealed up.

[jerkputter123]

Forgot to mention that he told me about few days before this chainsaw blew that it was running like it had never before. I asked to explain and he said it was screaming like a super saw. I told him the only thing normally that would cause that issue would be the saw was too lean. Now he will have to find what happened when he gets it back going or the same thing will happen again.

[StarTech]

Max. permissible engine speed with bar and chain: 13,000 r.p.m. 13,000 r.p.m.
Mean idle speed: 2,700 r.p.m. 2,700 r.p.m.

If these are being exceeded tune the rich side to slow down.

[jerkputter123]

Thanks for the info. His saw does not have the decompression valve. The engine assembly I found so far all as the decompression valve. His is a 49cc. Still looking. Thanks again.

[StarTech]

Thanks for the info. His saw does not have the decompression valve. The engine assembly I found so far all as the decompression valve. His is a 49cc. Still looking. Thanks again.

Sorry the .039 is not a 49cc engine. The .039 has a 49mm cylinder with a 34mm stroke and it is 64.1 cm3 (3.9 cu. in) so it is basically 64cc displacement saw.

You can use the PNC kit 49mm for Stihl MS390 chrome (PN 1127 020 1213). $51 including shipping of Amazon for the aftermarket PNC.

[bgsengine]

Thanks for the info. His saw does not have the decompression valve. The engine assembly I found so far all as the decompression valve. His is a 49cc. Still looking. Thanks again.

Some kits come with a plug to plug the hole for units that do not use decomp valve, some kits come with the decomp valve so you can convert the saw to use the valve just FYI. Also might want to replace the crank seals while at it (if they leak they can cause saw to run lean) and inspect the intake boot for any leaks or cracks.. (which will also cause lean running) we usually plan on replacing ALL rubber parts when doing a rebuild like that (intake boot, pulse hose, fuel lines, etc) and fresh fuel filter, just to eliminate "come-back" work because those parts are common failure and/or maintenance items anyhow. make sure muffler heat shield is in place, spark arrestor is clear, and crankcase has been well cleaned also.

[jerkputter123]

Thanks for the info. His saw does not have the decompression valve. The engine assembly I found so far all as the decompression valve. His is a 49cc. Still looking. Thanks again.

Sorry the .039 is not a 49cc engine. The .039 has a 49mm cylinder with a 34mm stroke and it is 64.1 cm3 (3.9 cu. in) so it is basically 64cc displacement saw.

You can use the PNC kit 49mm for Stihl MS390 chrome (PN 1127 020 1213). $51 including shipping of Amazon for the aftermarket PNC.

Sorry about that. I wrote the wrong information down.

[StarTech]

Yelp bgsengine those things do need checking and replaced if necessary. I just work on too many to remember the common sense things I do automatically so I do forget to mention those checks at times. Yes crank seal are commonly replaced items along with fuel lines. Intake boots not so much. New spark plug usually gets installed due aluminum coating of the old one.

These are basics of any rebuild that you check everything and replace the worn items as you do the rebuild. On straight gassed 2 cycles most of the damage is contained in the PNC so the other items are usually good. It when you don't know the cause is when you do things out caution and experience. It better to be over cautious then not.

Jerkputter, if you can I would recommend the modding to a decomp setup when available as long as you get a cylinder cover to match. Just note not all saws came with them or have them available later. Many of us older operators need all the help we can get on these larger saws when it comes to starting one. Actually anything above 42cc should have one. Boy some of old saws are hard to crank even using some tricks I have learned over the years.