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Author Topic: Stihl MS660 stopped itself at idle and won't start.  (Read 1433 times)

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Offline Tristimulus

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Stihl MS660 stopped itself at idle and won't start.
« on: October 30, 2017, 01:41:28 am »
I was reading this great resource for about a month, it the best one about mills from my point of view and archive is extemly valuable too.
I was trying to mill cedar using alaskan mill and Stihl MS660. Everything was fine.
Because cedar was to wide for my blade, I trim a bit cedar on one side. After I finished trimming and moved saw in vertical position in idle mode, and saw suddenly stopped. After that. I cannot start it.
I've checked everything I was thinking can cause problem:
Fuel lines (all clean), fuel filter(took it temporary off), added fuel in carburator manually (still no start even for one second), checked spark plug, it is fine (I can see spark in the dark room, so ignition is fine), looked at carburator in both input and output, everything is clean, but saw will not start.
What should I try to troubleshout more before going to repair shop?


Offline blueberrymuzik

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #1 on: October 30, 2017, 08:57:02 am »
You need fuel, air, spark, and compression to run. Compression is the next thing to check. 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.

Offline Caloren

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #2 on: October 30, 2017, 10:24:16 am »
Sounds like what happened to my log splitter the other day, stopped right in the middle of  splitting a log. Had spark, had fuel, wouldn't start. Sure enough, the key had sheared and it took a chunk out of the crankshaft at the edge of the keyway. Just finished installing a new crankshaft. Here's hoping yours is an easier fix!
Stihl MS 170, Stihl MS 310, Stihl 028 AV Super, and half a dozen other no-accounts! Cat D4 D.

Offline Tristimulus

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #3 on: October 30, 2017, 11:43:19 pm »
Blueberrymuzik:
Do I need some gauge to check compression?
The force which I need to apply to rope during pull is similair as before, so I suppect compression is good or good enough to work one or two cycles.
About key: if key in flywheel is broken, will it at least start working from manual pull for one or two cycles?
It is not starting at all, not even one cycle.
Strange

Offline PNWRusty

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #4 on: October 31, 2017, 08:47:48 am »
About key: if key in flywheel is broken, will it at least start working from manual pull for one or two cycles?
It is not starting at all, not even one cycle.
Strange


It's possible that it could "pop" with a sheared key, but chances are, it wouldn't. Because there are a lot more positions on 360 degrees of spark timing that won't fire vs. positions that will. Once the key is sheared, it's likely the last combustion cycle will force the flywheel to a position a position where there won't be enough compression to ignite the mixture at all.

On the compression question, I agree, if the compression feels normal as you pull the starter, that's probably not your problem. But a compression tester could eliminate the possibility that you're misjudging the feel.

Offline blueberrymuzik

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #5 on: October 31, 2017, 08:54:45 am »
Yes, you need a compression tester to check the compression of the saw. It is difficult to tell from just pulling the rope if you have sufficient pressure to start the saw.

If the key has sheared in the flywheel, the saw will not even try to start, since the spark will be arriving at the wrong time to the plug. The only way to tell if this has happened is to remove the starter cover, then remove the flywheel nut and use a flywheel puller to pull the flywheel off the crankshaft.

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #6 on: October 31, 2017, 09:52:20 am »
Pick up the saw by the rope . I it falls to the ground its scored . It should move slowly down stopping at each compression stroke . have you adjusted the carb . leaned it out to much . My processer saw will die after a cut if not adjusted right . Seems like I need to adjust almost each day in the fall .
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 #7 on: October 31, 2017, 12:37:18 pm »

I've tried to pull by the rope and it did not fail on the ground. I felt about 3 cycles of cilinder where it slowed down (almost stopped on each cycle). I will try to disassemble ignition system on Wednesday and see if something wrong with flywheel.
I never touched carburator adjustment settings. I hope those settings are not so bad, so it will not even pop for one or two cycles.

Offline JMoore

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #8 on: October 31, 2017, 01:42:03 pm »
I don't know about that saw in particular or much about saws in general but just recently had a 30cc sthil blower that did the same exact thing and the spark arrestor was clogged. Burned off all the gunk and it went back to running like new.i did this after new plug and new carb neither of which fixed the problem.

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #9 on: October 31, 2017, 05:49:58 pm »
I also had a 270 Stihl that just quit . Turned out it was the coil . The dealer said it happens sometimes .
A bunch of chainsaws a BT6870 processer and not near enough time

Offline plantman

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #10 on: October 31, 2017, 08:01:10 pm »
I don't know about that saw in particular or much about saws in general but just recently had a 30cc sthil blower that did the same exact thing and the spark arrestor was clogged. Burned off all the gunk and it went back to running like new.i did this after new plug and new carb neither of which fixed the problem.

By "spark arrestor" I assume you mean that little piece of screen they put behind the muffler. On all my two cycle equipment I take that out ASAP. Plus, you need to use 93 octane gasoline and the correct mix of oil. Not too much and not too little. If you use regular gas it won't burn hot enough to burn the oil and it gums up that screen. Just remove the *DanG thing. Stupid safety crap.

Offline Tristimulus

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #11 on: November 01, 2017, 04:59:26 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.

Offline plantman

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #12 on: November 01, 2017, 06:24:07 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 ?

Offline HolmenTree

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #13 on: November 01, 2017, 09:37:09 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 ?
Actually our Shell premium up here in Canada is good stuff. 92 octane no ethanol and our local marina  also keeps it for sale.
Making a living with a saw since age 16.

Offline Crusarius

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #14 on: November 01, 2017, 11:13:26 am »
That spark arrestor is there to prevent special ppl from starting forest fires. It may be considered a safety feature but it is not for the user, it is for all the homes that will get burned during a forest fire.

End this public service announcement. Please carry on with your normally scheduled day.
I knew what I thought I meant.

Offline thecfarm

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #15 on: November 01, 2017, 02:02:12 pm »
Don't want to be harsh either,but I've had saws since I was 20 years old,had 4-5 saws and yes,I've had trouble with a few spark arrestor,but I have a 372 husky and have never cleaned it yet. I use the highest grade of gas that I can get at 40:1.  ;D
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Offline ehp

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #16 on: November 01, 2017, 02:15:33 pm »
sounds like lean burn to me, take the outside cover off the muffler , it has 4 screws that hold to together , take flash light and look in ext. port and roll piston to TDC and look the piston threw the port , Im pretty sure your going to find the piston is torn up pretty good

Offline PNWRusty

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #17 on: November 01, 2017, 02:42:46 pm »
Plus, you need to use 93 octane gasoline and the correct mix of oil. Not too much and not too little. If you use regular gas it won't burn hot enough to burn the oil and it gums up that screen.

That's not true. You don't need 93 octane! There's nothing wrong with running 93 octane but it's not necessary. Anything 89 octane or higher will work just fine. It's important that it's fresh and properly mixed but it won't run any better or make more power on 93 octane. Fuel does lose octane points over time so going with 91 octane or higher is good but it's more important to keep it fresh and mixed with a high quality oil to the proper ratio. Adding too much oil leans the mixture out unnecessarily.

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #18 on: November 01, 2017, 07:18:20 pm »
PNWRusty I think all understand that the idea of high octane is to make sure you get non oxy . Saws will run just fine on fresh oxy fuel . Chain saws that many own sit for months at a time . That is where the problem comes from or from the gas can that sat for a year or more .
A bunch of chainsaws a BT6870 processer and not near enough time

Offline PNWRusty

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Re: Stihl MS660 stopped itself at idle and won't start.
« Reply #19 on: November 02, 2017, 12:34:07 pm »
PNWRusty I think all understand that the idea of high octane is to make sure you get non oxy.

Apparently not everyone understands that because the statement was that 93 octane was necessary.

What's "non oxy"? I would assume you are speaking of non-oxygenated fuel but that doesn't make sense because even premium grade pump gas typically contains oxygenates, just as much as the lower grades. In other words, buying 93 octane does not mean it won't have 10% ethanol.

 
Quote
Saws will run just fine on fresh oxy fuel . Chain saws that many own sit for months at a time . That is where the problem comes from or from the gas can that sat for a year or more .

I would never recommend using pump fuel over a year old. Even if it's 93 octane. Yeah, you can probably get away with it if it's been stabilized but it's not a good practice. If you're gonna let your gas sit around that long you should really be buying the higher quality fuels that come in a can because they are formulated with more stable distillates (like Stihl Moto-Mix). Typically even the premium grades of pump gas are oxygenated. So I'm not clear on what you're saying there. Even before we had oxygenated pump gas it was bad practice to let gas sit around a year or more.   

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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)

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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

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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!!
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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.


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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
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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.


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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