MS 390 Reassembly

[heyduke]

Sorry, no offense meant. I priced the oem bearings last week at my dealer. Like $16, it was Stihl that frustrated me.

The reason I priced the bearings at the dealer was because I have 7 open saws on my bench and wanted to close one.

There's a 015av on my bench for 6 weeks waiting on a Stihl gasket set that's paid for.

My problems are not with the dealer or with you, it's Stihl and their parts and policies. Intermountain Stihl is in Denver where my dealer is with three stores and they can't get me a gasket set so I can get two seals for $26?

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no offense, i agree with you. i refrain from making comments about stihl and its company culture because there are so many guys on this forum with a religious devotion to orange and cream. i'm a little south of you in northern new mexico and most of the hombres here think if you're not cutting with a stihl there's something wrong with you and the funny thing is that they're mostly using these little 039's and other "homeowner" stihls that are nothing to brag about. and when they take them to the dealer for service they find that bar oil has another use. often those saws find their way to my bench. The standard operating procedure for our local dealer is to give you a repair estimate that is $60 less than a new saw. then he charges you $60 for the estimate.

on the other hand, i'm doing the numbers on the 029 now. i'll be lucky if i get by with less than $200 in parts and materials, using a hyway kit and non-oem seals and bearings. the saw isn't worth much more than that.

 

[heyduke]

The OEM bearings (with plastic retainers) says "made in Turkey". I feel no remorse at all with replacing them with asian bearings with metal retainers.

Don't blame the fine Turkish people. It's the suits from Stihl that order low quality bearings.

 

[cedarshark]

Don't blame the fine Turkish people. It's the suits from Stihl that order low quality bearings.

The Turkish bearings would have been fine were it not for the compression release bearing rattling around in one of them. Same thing would have happened to a Asian,German or American bearing.

 

[heyduke]

The Turkish bearings would have been fine were it not for the compression release bearing rattling around in one of them. Same thing would have happened to a Asian,German or American bearing.

Well, that's not arguably true. The plastic retainers are cheap and prone to failure. You don't really know what the root cause of your catastrophic failure was. It might have been debris from a failing crankshaft bearing that damaged the compression release valve. I've never seen a decomp valve fail that way. Occasionally they quit sealing well but that's about it. But again, let me remind you that these were not Turkish bearings. The specifications were written by Stihl engineers and a Turkish manufacturer, among others, built them to spec.

 

[cedarshark]

Heres what I do know:

1) The crank was locked with a small ball lodged under the crank lobe.
2) The piston top was dimpled slightly in the area of the compression release. There was no damage to the sides of the piston or the cylinder walls. I suspect the ball bearing got to the crankcase via a transfer port.
3) The compression "pin/shaft" was in the muffler.
4) Inspection of the OEM bearings (w/ a magnifying glass) indicated no damage to the bearing retainers. I wanted to know why I failed to recognize the bad bearing on the first teardown. No pieces of the retainer were in the bearings or in the crankcase. All the crank bearing were adequately seperated. There were bearing balls that appeared to be dimpled or scored, probably because the loose ball made it into the bearing briefly before lodging under the crank lobe.

I find it very difficult to believe a piece of plastic retaining ring did enough damage to a closed decomp valve while running to shatter the decomp valve. I believe the decomp valve failed at or slightly before startup thereby causing minimal damage
. If it would have happened at full throttle, I think the damage would have been much more severe. Whatever the reason, it was enough for me to remove all decomp valves on the saws I own and plug them. Just one less thing to worry about. A comp release on a saw of less than 70 cc is like "teats on a tarapin"......pretty useless. If Stihl thought my 044 does not need a compression release....why did they put one on a 390 or worse yet...an 026 Pro ? Marketing is why....lets add a decomp and adjustable oiling and charge a premium.

I guess I am little weird. All this hype about the clamshells not worth the effort to fix or rebuild. I kind of enjoy them. I just bought another 039 from the Stihl dealer today that they convinced a customer was "not worth fixing" .

But...you are absolutely correct....its all just speculation. Cheers and thanks for your input.

 

[heyduke]

Heres what I do know:

1) The crank was locked with a small ball lodged under the crank lobe.
2) The piston top was dimpled slightly in the area of the compression release. There was no damage to the sides of the piston or the cylinder walls. I suspect the ball bearing got to the crankcase via a transfer port.
3) The compression "pin/shaft" was in the muffler.
4) Inspection of the OEM bearings (w/ a magnifying glass) indicated no damage to the bearing retainers. I wanted to know why I failed to recognize the bad bearing on the first teardown. No pieces of the retainer were in the bearings or in the crankcase. All the crank bearing were adequately seperated. There were bearing balls that appeared to be dimpled or scored, probably because the loose ball made it into the bearing briefly before lodging under the crank lobe.

I find it very difficult to believe a piece of plastic retaining ring did enough damage to a closed decomp valve while running to shatter the decomp valve. I believe the decomp valve failed at or slightly before startup thereby causing minimal damage
. If it would have happened at full throttle, I think the damage would have been much more severe. Whatever the reason, it was enough for me to remove all decomp valves on the saws I own and plug them. Just one less thing to worry about. A comp release on a saw of less than 70 cc is like "teats on a tarapin"......pretty useless. If Stihl thought my 044 does not need a compression release....why did they put one on a 390 or worse yet...an 026 Pro ? Marketing is why....lets add a decomp and adjustable oiling and charge a premium.

I guess I am little weird. All this hype about the clamshells not worth the effort to fix or rebuild. I kind of enjoy them. I just bought another 039 from the Stihl dealer today that they convinced a customer was "not worth fixing" .

But...you are absolutely correct....its all just speculation. Cheers and thanks for your input.

There's nothing I can argue with here. I've never seen a decomp valve fail like that but anything is possible. Maybe the same engineer who wrote the bearing specs worked on the decomp valve. I think you got me going when you inferred that Turkish people were somehow inferior to us. I've been fortunate to know a few and I'd have to disagree with you there. Don't EVER play backgammon for money with a Turkish person.

Regarding clamshells, I agree with you on that too. I'm about to do my first one, an 029 upgrading to an 039 top end, and looking forward to the experience. I'll try to post some fotos and analysis. I think there is a lot of value in being able to access the crankshaft bearings and seals without a suite of special, expensive tools, and you can replace bearings and seals any time you do top end work. Truth is some of the hottest 2 strokes, like cart engines and motorcycles, are clamshell designs. I have worked on quite a few clamshell saws, top handle climbing saws, but I've never seen one that needed much more than minor repair or new plastic after being run over or dropped from a tree. Same regarding the decomp valve on a 60cc class saw. What were they thinking? They saved fifty cents on bearings and spend five bucks for decomp on a saw that any sissy can turn over, my apologies to sissies.

 

[cedarshark]

I have great respect for the Turks production ability. They make some beautiful shotguns. I hope you post some pics of your 290 to 390 conversion. I understand it is pretty straightforward but have not done it personally. I know the Hyway kits have a following but I am more comfortable with the Meteor kit, if one is available. I just put a Hyway piston in an 024 but it has not been tested fully in wood.

 

[anlrolfe]

I found another video for 290/310/390 assembly. It begins with inserting the completed clam shell into the chassis.

Its a LONG video, almost 1-hour.

 

[cedarshark]

My 390 is back together and running well. I learned you can pull the av bushing into the housing in a similar way as you pull the intake boot thru the housing using a looped piece of string. Much easier to do. Thanks for the video!

 

[Wood Doctor]

My 390 (an upgrade from a 310) is also running nicely. However, a vintage Stihl 038 AV that my friend let me borrow will run circles around it and cut faster without breathing hard. I think I would have been better off buying his saw, which is 18 years old and runs like a bandit, rather than spend hours trying to save a 390.

 

[cedarshark]

038 has loads of torque but I have not run my 039 yet....needs a new sprocket