MS 390 Reassembly

[griffonks]

I use aftermarket seals from Weedeaterman.com, highway pistons too, they run fine.

On the first one I did I used all Stihl parts. Right now I have an OEM 390 and a 290/390 with a Highway piston in a NWP jug. The 290/390 has more compression.

Also it has a bridge over the transfers, poorer finish work in the ports though. 20 minutes with a grinder fixed that.

So folks show up to dicker for the OEM MS390 then I tell them have an Asian conversion for a little less $. They leave with the conversion every time.

Stihl puts plastic bearings in the sprocket and on the crankshaft ends..... Asian sets are steel for less.

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[griffonks]

Here's the current crop of seller's, pardon the bad pic it's getting dark:

026, MS390 with old school caps/crankcase, 290/390, and a MS250. There are two more 025's in a box and a nice MS200t engine, pto and carb- needs a body, man they are hard to find now.

I like repairing Stihl homeowner saws because they sell easily, AM parts are easy to find, and they sell for too much money. I build Huskies for me with the money, lol...

 

[cedarshark]

Thats a nice crop of saws. I use mostly meteor pistons but am about to try a Hyway piston in a 024 that scored a piston. The hyway is cheaper than meteor. It will be interesting to compare quality. The MS200 (running or not) sell for crazy prices.

 

[griffonks]

I have only used Hyway's on clamshells. They seem better than the rest except for Meteor, Episan, or Tecomec. I had a poor Hyway piston and rings in a NWP Bailey's kit, but the Hyway's I buy from Weedeaterman are ok. It was like the NWP kit had an earlier Hyway piston (stamped with the stylized H under the crown) or one made with lesser quality. The rings were a two peice design.... nasty looking.

The NWP kit was bought from Bailey's two years ago and failed almost immediately. The NWP jug was ok though, just minor rough casting in the ports.

Did you reassemble your MS390 yet?

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[SawTroll]

If you used a sledge to disassambe it, like you should, there isn't much hope of reassambling it into a working saw......

 

[cedarshark]

I have only used Hyway's on clamshells. They seem better than the rest except for Meteor, Episan, or Tecomec. I had a poor Hyway piston and rings in a NWP Bailey's kit, but the Hyway's I buy from Weedeaterman are ok. It was like the NWP kit had an earlier Hyway piston (stamped with the stylized H under the crown) or one made with lesser quality. The rings were a two peice design.... nasty looking.

The NWP kit was bought from Bailey's two years ago and failed almost immediately. The NWP jug was ok though, just minor rough casting in the ports.

Did you reassemble your MS390 yet?
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I Bbq'd a brisket,pork butt and ribs early this morning so had some time work on the 390. It went together fine fired right up but I did a poor job of assessing the condition of the bearings. Nasty growl while saw is running,even at idle. I double checked and idled it with the clutch drum(and bearing) off....growl still there. The further I got into this saw,, the more I believe it was under water for a while. The drum was rusted to the clutch, the muffler was full of rust and I bet, if an autopsy were done the bearings have rust in them. I will see what a set runs and decide if i want to tear this saw down again.

 

[cedarshark]

If you used a sledge to disassambe it, like you should, there isn't much hope of reassambling it into a working saw......

I cant think of a whole lot of nice things to say about clamshells.....but replacing bearings will be easier.

 

[cedarshark]

Broke the 390 down again today and pulled the bearings. I found the bad one by placing the bearing on my finger and slowly rotating it. Every other rotation, it would "catch" on something and I could feel the rough spot. I did not notice the rough spot with the bearings on the crank. Took a stout 2 jaw puller to get the bearings off.

How hot should the oven be to warm the bearings before placing them on the crank?

 

[anlrolfe]

I've always done it like this:



No gear puller required

 

[cedarshark]

Very informative video and thanks for sharing. It is almost impossible to get a square pull on those bearings with a puller because they are so close to the crank lobes. I will try your method to install the new ones. I assume if you go back with OEM bearings(with the plastic races) that heating the inner race with a torch may not be a good idea ?

 

[heyduke]

Very informative video and thanks for sharing. It is almost impossible to get a square pull on those bearings with a puller because they are so close to the crank lobes. I will try your method to install the new ones. I assume if you go back with OEM bearings(with the plastic races) that heating the inner race with a torch may not be a good idea ?

The vid makes me wonder if the debris you found at the bottom of the case was actually from the crank bearing rather than the compression relief valve. what tool did you use to pull the flywheel? i'm starting an 029 to 039 rebuild in the next few weeks, my first clamshell. this thread has been informative.

 

[griffonks]

You can buy a flywheel knocker cheap or hit the barely loosened nut with a brass drift or hammer. I like hitting clammys...

As for the bearings I used to worry about staying OEM with Stihls, but here is no way I'm gonna pay that much for plastic races. So far I am 100 0/0 satisfied with Asian AM bearings from Weedeaterman. $15/ pair.

Huskys are different because I can get cheap enough skf's to fit.

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[heyduke]

You can buy a flywheel knocker cheap or hit the barely loosened nut with a brass drift or hammer. I like hitting clammys...

As for the bearings I used to worry about staying OEM with Stihls, but here is no way I'm gonna pay that much for plastic races. So far I am 100 0/0 satisfied with Asian AM bearings from Weedeaterman. $15/ pair.

Huskys are different because I can get cheap enough skf's to fit.

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yeah, the crank bearings on these look like junk. i suspect they are the root cause for the piston scoring on the 10 year old 029 i'll be working on. it's a shame that stihl uses those cheap bearings. they couldn't be saving more that a couple of bucks per unit. i suppose their idea is to have the "true believer" return in a few years for a new saw. i think that worked in this instance. this saw was thrown away and another stihl was purchased. i just ordered two pullers, one a knocker, the other the threaded type that screws into the ring on the flywheel. they're supposed to work on most stihl models. i'm thinking a 039 hyway kit from weedeaterman. i'll order the other stuff at the same time. I've always had good experiences with huskies, both the four legged kind and the orange ones too.

 

[griffonks]

yeah, the crank bearings on these look like junk. i suspect they are the root cause for the piston scoring on the 10 year old 029 i'll be working on. it's a shame that stihl uses those cheap bearings. they couldn't be saving more that a couple of bucks per unit. i suppose their idea is to have the "true believer" return in a few years for a new saw. i think that worked in this instance. this saw was thrown away and another stihl was purchased. i just ordered two pullers, one a knocker, the other the threaded type that screws into the ring on the flywheel. they're supposed to work on most stihl models. i'm thinking a 039 hyway kit from weedeaterman. i'll order the other stuff at the same time. I've always had good experiences with huskies, both the four legged kind and the orange ones too.

You will like the Hyway kit, may as well go whole hog and do the impulse hose and the fuel line while you are in there. I've heard it said that Stihl uses plastic races to limit damage if a bearing comes apart.... I think that's BS....

Maybe you can get by with cleaning the jug.... buy the hyway piston and rings

 

[heyduke]

You will like the Hyway kit, may as well go whole hog and do the impulse hose and the fuel line while you are in there. I've heard it said that Stihl uses plastic races to limit damage if a bearing comes apart.... I think that's BS....

Maybe you can get by with cleaning the jug.... buy the hyway piston and rings

that line about the plastic races is what i call peeing down my back and telling me that its raining. i'll be buying a cylinder. i want to upgrade from 56cc to 64cc. i have used and earlier hyway cylinder and piston. it wasn't great but i've heard that they have improved.

 

[cedarshark]

The vid makes me wonder if the debris you found at the bottom of the case was actually from the crank bearing rather than the compression relief valve. what tool did you use to pull the flywheel? i'm starting an 029 to 039 rebuild in the next few weeks, my first clamshell. this thread has been informative.

It was the compression relief valve. The ball in the crankcase was very small...way smaller than a crank bearing

 

[cedarshark]

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.

 

[cedarshark]

I've always done it like this:



No gear puller required

et

I tried this method anlrolfe described in his video and it worked perfectly. Very easy and the bearings dropped in place.

 

[anlrolfe]

cedarshark said: "method anlrolfe described in his video"

Not "my" video, just one that does a really good job showing the repairs

 

[griffonks]

that line about the plastic races is what i call peeing down my back and telling me that its raining. i'll be buying a cylinder. i want to upgrade from 56cc to 64cc. i have used and earlier hyway cylinder and piston. it wasn't great but i've heard that they have improved.

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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