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Author Topic: Stihl MS660 stopped itself at idle and won't start.  (Read 1421 times)

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Offline Gearbox

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #20 on: November 02, 2017, 07:12:33 pm »
Where I live and many other states have collector car fuel . NO ethanol in our state there is a sign on the pump that states no ethanol .
A bunch of chainsaws a BT6870 processer and not near enough time

Offline Tristimulus

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #21 on: November 03, 2017, 02:46:40 am »
Just to comment on gasoline: I'm using Pure Premium gasoline (Shell) (no ethanol) with stihl brand oil (HP Ultra 2-Cycle Engine Oil) in 50:1 mixture, so I suspect fuel is not an issue in my case.

Where do you purchase that gasoline ? At a boat yard ?

In Canada (at least in BC) Shell is selling Premium gasoline ethanol free.

Offline Tristimulus

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #22 on: November 03, 2017, 03:01:08 am »
Update on the debugging:
I looked at flywheel today and it is fine, no damage to anything including key.
Also tried again spark plug and it is producing sparks fine, I can see it. Spark plug is almost new by the way.
Looked at both sides of carb and they both clean, no debris or anything and no damage to membranes or diaphragms and spring with needle looks fine.
Fuel is definitely coming from tank, but probably not coming out of it or something else is not working correctly.
I'm running out of time with milling my cedar, so I will take it to a dealer tomorrow and see what they will tell me.


Offline joe_indi

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #23 on: November 03, 2017, 03:48:08 am »
.......The only other thing that comes into play, is timing. If your compression is good, pulling the flywheel would let you see if the key has sheared.
yes! The first thing I would check in such a situation. A moving flywheel that has caused a key to shear would shift forward. This is easily verified if the spark plug is removed and a pencil or screwdriver is inserted onto the piston top and the engine is turned over slowly (anti Clockwise at the flywheel)m When the N and S on the flywheel are aligned  with the poles of the ignition  module, if the key is sheared the piston will be nowhere close to TDC

Offline ZeroJunk

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #24 on: November 03, 2017, 07:50:48 am »
It is likely that the first thing the dealer will do is look at the piston through the exhaust port.

If you mess with saws a lot you can tell from the "thump" it makes when you pull the rope.

The falling saw from the handle doesn't tell you so much because a lot of things can keep the saw from falling other than compression.

Offline Chop Shop

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #25 on: November 04, 2017, 02:35:43 am »
How many folks have had a saw "Shear a key"

Ive run ALLOT of saws, burned hundreds of gallons, cut tons of wood, and even killed a few saws in my day.

Ive NEVER EVER seen a saw with a sheared key.

But Ive seen dozens with burnt pistons.  Plenty burnt by MILLING slabs/lumber.

My bet is on a smeared piston/rings.

(PS, its much easier to pull a muffler than a flywheel)

Offline ehp

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #26 on: November 04, 2017, 10:42:51 am »
I have seen more than a few broken keys on Stihls but Im still thinking pull the outer muffler cover and look at the piston skirt . Milling boards is real hard on a motor and the engine gets real hot

Offline joe_indi

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #27 on: November 07, 2017, 03:42:26 am »
If the key is not sheared and everything else looks OK, the usual cause on a 066/660/046/460 is the polymer flywheel going out of timing due to a twisted base.
This can be verified only by having another good flywheel to compare with.
Place both flywheels one above the other with  N and S of both aligned.
Then examine the centers if the key grooves are not aligned, it verifies a twisted flywheel.
Nothing can be done other than a flywheel replacement.

Offline smoked

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #28 on: November 07, 2017, 07:22:51 am »
I can't remember where I read it but there is a very good article on why premium fuel and proper mix out there.  Bottom line, octane is not about power, it is about controlled combustion vs detonation.  Detonation creates very nasty internal forces on the engine.  My manuals call for premium so I will pay the $.40 extra a gallon for it.  Also, if memory serves me, more oil in the mix drops the octane rating so that extra oil may burn your piston in the long run too >:(

OP, hope you get your big saw sorted out!!
Hobby woodworker/wood burner
If I screw something up, it is free heat next winter:-)

Offline plantman

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #29 on: November 07, 2017, 07:51:04 am »
Anyone ever try to make ethanol free gas themselves ? Is it worth doing ? Or is it just better to add a ethanol treatment ? I think Lucas makes one.


Offline smoked

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #30 on: November 07, 2017, 09:34:28 pm »
Here is some of what I read on mix and octane.  http://www.madsens1.com/saw_fuelmix.htm
Hobby woodworker/wood burner
If I screw something up, it is free heat next winter:-)

Offline Tristimulus

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #31 on: November 10, 2017, 02:40:52 am »
Update from the dealer:
He disassembled the engine and found what piston was scored and cylinder has some damage.
From his point of view it was overheated due to hi revs or not enought lubrication or both.
I should have done it myself, but I hopped it is some other issue, not piston.
I will rebuild this one (I hope it is not difficult (never did it before)),  but I don't have time to do it now, so I need to buy another one in order to finish my milling. I only need 2 cuts to finish my last log.
I can buy new MS661 (power head only) for 1025$US or 1300$CAD or I can buy a built one from ground up using stihl and aftermarket parts MS660 for 590$US or 750$CAD.  3 months warranty

So my dielema is which one to buy: 660 or new 661?
Thanks a lot for all replies, I've learned a lot.


Offline Gearbox

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #32 on: November 10, 2017, 08:40:47 am »
Ask your dealer if he will do it with after market parts and vacuum and pressure test AFTER to make sure the every thing is sealed . You may  have been out of adjustment or it could be seals . Let a pro do it . I tried and melted down a 272 three times . turned out someone scored a case with a screwdriver getting a seal out .
A bunch of chainsaws a BT6870 processer and not near enough time