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Author Topic: Stihl 090  (Read 3392 times)

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Offline Flash

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Stihl 090
« on: January 20, 2017, 07:16:46 PM »
I have a question please regarding the clutch on my Stihl 090 chainsaw. When I start the saw the chain will move quite rapidly as there is no chain break on this model of saw. This is very dangerous and something I would like to stop if possible. I have noticed other 090 saws on the web idlying along with the chain hardly moving at all which is what I would like to achieve.

I have pulled off the cover to reveal the clutch and with the chain on the bar the outer casing of the clutch doesn't spin freely and contacts the shoe or shoes. When I take the bar off, the outer casing spins freely with little to catching of the shoes.

This saw has been in service by a friend used in the forestry and has seen some hard work in the past. is it possible that the springs in the clutch have relaxed over time (40 years) and let's the shoes contact the outer casing when the bar and chain are on the saw, or is some other underlying issue?

Thanks in advance for any suggestions as to a possible remedy.

Cheers,
Flash

Offline SawTroll

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Re: Stihl 090
« Reply #1 on: January 20, 2017, 08:04:04 PM »
Just an immediate hunch, this may not have anything to do with the clutch - but simply that the idle rpm is too high. If that can't be corrected by adjusting the idle screw and/or the "L" screw of the carb, there likely is an air leak somewhere.

I have no experience with that particular model though, so that just is general information.
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Offline Gearbox

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Re: Stihl 090
« Reply #2 on: January 20, 2017, 08:07:59 PM »
Broken clutch spring ? Replace them all .
A bunch of chainsaws a BT6870 processer , TC 5 International track skidder and not near enough time

Offline Flash

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Re: Stihl 090
« Reply #3 on: January 21, 2017, 05:32:31 AM »
Thanks for the suggestions. The idle was was set at its last service and I did remember the mechanic saying that he had trouble getting the chain not to move at the lowest revs practical. Think I will go with replacing the springs and giving the shows and internal surface of the drum a good clean and a light sand if need be.

Thanks
Flash

Offline HolmenTree

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Re: Stihl 090
« Reply #4 on: January 21, 2017, 01:16:09 PM »
Sounds like you have a clutch drum wobble. Drum bearing is probably worn out.
Making a living with a saw since age 16.

Offline joe_indi

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Re: Stihl 090
« Reply #5 on: January 21, 2017, 11:44:42 PM »
..............I have pulled off the cover to reveal the clutch and with the chain on the bar the outer casing of the clutch doesn't spin freely and contacts the shoe or shoes. When I take the bar off, the outer casing spins freely with little to catching of the shoes.

This saw has been in service by a friend used in the forestry and has seen some hard work in the past.........
Though I have not handled one before, the 090 looks to be a saw with an outboard clutch, no rim sprocket but a spur sprocket. Its seen a lot of use.
In addition to what has suggested by Holmen, I would inspect that spur for wear. If worn too much the drive links would stick.
Being so old we cannot say that the needle cage has ever seen the light of day, or whether it has been cleaned (of resin) and lubricated.
Resin build up on the inner surface of the clutch drum could eliminate free play leading to the clutch being in contact with the drum always (via the resin/sawdust deposits)
Maybe removal of the clutch and drum and a thorough cleanup followed by some grease on that needle cage might make things a lot different, unless the drum is badly worn as suggested by Holmen

Offline Brad_bb

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Re: Stihl 090
« Reply #6 on: January 22, 2017, 12:49:11 AM »
Flash, I have an 090.  I bought it 2 years ago on ebay from a guy out in Washington State.  Looked like he bought it in the late 70's or early 80's and used it a dozen times or so to chainsaw mill redwood slabs(he told me that), and then it basically sat on the shelf.  When I got it was really hard to start and would not make power. 

Although the saw looked great on the outside, dealer looked at it and said it needed a new carb(corrosion from sitting).  We did that, and it started easily enough but would not make power under load and adjusting the WOT mixture screw did nothing.  Turned out to be a crankcase gasket air leak.  So I got an aftermarket gaskets and seals (no longer avail from Stihl), the mechanic rebuilt.  It started easy, but there was definitely a learning curve to adjusting the idle mixture, idle speed, and WOT mixture screw. 

My chain moved as you describe at first, but then my idle speed and carb mixtures were not right.  Idle speed adjustment is actually a throttle start position adjustment - how much air could come in at idle.  Well if you turned the idle speed down low enough to stop the chain, the saw would die (due to mixture/air problem caused by carb and gasket air leak). 

Once I had the new carb and we solved the air leak, I was able to learn how to adjust it.  First set the idle mix and WOT mix at factory setting.  I have the manual out in my shop.  I can get it tomorrow to verify the factory setting.  I think it was 7/8 turn from closed.  Then you can adjust your idle speed down to stop your chain.  You may need to adjust the idle screw to find optimum idle.  Then you set the WOT (Wide Open Throttle) mix screw.  Hold throttle wide open and adjust to max RPM. 

NOTE:  If you change temps significantly, you will need to readjust your mix screws.  I went from 65F in my shop adjusted for that, to 14F outside and they needed readjustment.  Saw didn't idle nice, or make full power until I adjusted them.  the adjustment is within a 1/4 turn range.  Just a small 1/16th or 1/8 turn can make a big difference.  It's not bad, it's just understanding and getting a feel for the proper idle, and when it's making full power.

I did a video on all the frustration:


And here is a cutting video after I was comfortable with the adjustments:


Once you are sure you don't have an air leak like my crankcase gasket leak, if your saw dies under load, the WOT mix screw is not adjusted right.  First make sure your idle mix is optimum, then adjust your WOT as I described earlier -hold throttle wide open and adjust screw to max RPM.

Anything someone can design, I can sure figure out how to fix!
If I say it\\\\\\\'s going to take so long, multiply that by at least 3!

Offline HolmenTree

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Re: Stihl 090
« Reply #7 on: January 22, 2017, 01:13:32 PM »
When you get your carb settings all straightened out. Check the wind vane governor beside the flywheel.
There's a pre wound spring on it that is tensioned to    control the choke shutter on the carb to richen up the saw at WOT.
There's about 6 tooth notches that the spring's tail is set in sealed with a spot of resin from the factory.
Both of my 090s from brand new were set on the 2nd notch. I put the spring on the last notch which increased the tension giving me a little better WOT.

But in the recent past I have wrapped the spring tail all the way around the wind vane axle and re hooked it on the first notch which completely disabled the choke shutter govenor.
This made my 090 a totally different saw with an increase of about 1500 + rpm at WOT.
With proper carb settings and premix at 40:1 the saw has cut hundreds of 54" diameter paper rolls at the local paper mill and milled thousands of feet of lumber.
Saw is still making about 200 lbs of compression, crank bearings are still tight. Never had the cylinder off.
Making a living with a saw since age 16.

Offline Al_Smith

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Re: Stihl 090
« Reply #8 on: January 22, 2017, 08:11:08 PM »
There might be something to think about here .First I've never worked on one so it's second hand info .If memory serves the 090 uses a faced clutch in other words a facing like a brake shoe on the clutch segments .It might be possible the facing is loose hanging the clutch a bit .Just a thought .

Offline Brad_bb

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Re: Stihl 090
« Reply #9 on: January 22, 2017, 11:24:14 PM »
HolmenTree, my original manual says 25:1 for oil/fuel.  Why 40:1??
Anything someone can design, I can sure figure out how to fix!
If I say it\\\\\\\'s going to take so long, multiply that by at least 3!

Offline Al_Smith

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Re: Stihl 090
« Reply #10 on: January 23, 2017, 06:03:48 AM »
If I may interject a thought .When that saw was built every manufacture suggested heavier oil mix unless you were using their brand of oil .McCulloch did the very same thing with suggested ratios .One might take note the "oil wars " are quite old . They are still amusing from my perspective . ;D

Offline HolmenTree

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Re: Stihl 090
« Reply #11 on: January 23, 2017, 10:42:56 AM »
HolmenTree, my original manual says 25:1 for oil/fuel.  Why 40:1??
Brad, looks like your 090 is about 20 or more years older then mine.
My 090 is one of the very last ones sold new in North America.
Here's my owner manual it says inside 1993 Andreas Stihl, Waiblingen
I bought it brand new in 1995.

Here's some pics, read the 40:1 information in the 2nd pic like what Al Smith said.
Hopefully they might help the OP Flash with his problems.
 

  

  

  

  

 
Making a living with a saw since age 16.

Offline Flash

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Re: Stihl 090
« Reply #12 on: January 24, 2017, 06:02:42 AM »
Thanks everyone for your input. So much knowledge out there which is a pleasure to read. I take all of your advice on board and will be relaying your comments to my small motor mechanic to try and rectify this problem I have.

I have actually had the clutch apart previously and did an inspection of the components as well as the needle bearing which I cleaned throughly and repacked with grease.

I will let you know the outcome in due course.

Thanks again,
Flash

Offline HolmenTree

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Re: Stihl 090
« Reply #13 on: January 24, 2017, 07:54:32 AM »
Flash, very important how you reassemble that clutch.
I had your problem once and found I reassembled the washers wrong.

Welcome to the site BTW  :)
Making a living with a saw since age 16.

Offline Flash

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Re: Stihl 090
« Reply #14 on: January 25, 2017, 12:01:14 AM »
Thanks for the heads up on reassembling the clutch, will keep that in mind.


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