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Stihl MS660 stopped itself at idle and won't start.

Started by Tristimulus, October 30, 2017, 01:41:28 AM

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Chop Shop

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)

ehp

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

joe_indi

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.

smoked

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:-)

plantman

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.

https://www.youtube.com/watch?v=onCG7mIprfE

smoked

Hobby woodworker/wood burner
If I screw something up, it is free heat next winter:-)

Tristimulus

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.


Gearbox

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 , TC 5 International track skidder and not near enough time

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