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Stihl MS 660 - (are there any Stihl service guys out there!!)

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Would anyone be able to tell me if I'm getting ripped off by my current service guy. I have a Stihl MS 660 that is used for ringing up large butts at the log barn.

 

It wasn't starting so I took it in and they have said that the fuel in the tank was dirty and this had clogged up the Carb filter (having passed through the fuel tank) filter and it had caused the saw to run lean and heated up and siezed the piston in the cylinder.

 

Is this something that anyone has heard of happening before, and would the compensator device in this type of saw control this?

 

This saw doens't get used often, and has probably only done three days of work, since the last time it was at the shop, where they told me it needed a new piston caused by 'dirty fuel'.

 

I run 7 other saws, two 024's and 5 MS200t's all on the same fuel and no problems with this.

 

Please does anyone know (if there is a Stihl service engineer here) if this is something that I've just been unlucky with, or am I begin bullsh**ted by this place.??

 

Please help!!

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I am not a Stihl service agent but have done a few 066/660s, firstly, if the tank breather is blocked, it is possible you may be able to get the saw to lean out when flat out but would have expected it to have been idleing badly and bgging down due to lack of fuel in the lead up to failure - has the saw carb been adjusted recently?

 

It is unlikely any muck of any volume would get past the fuel filter and if it did, it would end up in the gauze filter in the pumping section of the carb.

 

The most common causes of failure are

 

airleaks - easy to diagnose with a vacuum/pressure check

 

Carb set too lean - some don't understand the settings with the limit caps in place and removed or just badd adjustment

 

Old or neat fuel - doesn't sound like this happened.

 

If the saw is seized, the piston will have vertical scores on the exhaust side of the piston, easily checked by removing the exhaust. it will also have very poor comression.

 

The saw will typically falter and slow down before dying and fail to restart after a long cut or long cuts when the saw is hot.

 

I wouldn't like to cast judgement on other engineers diagnosis but I am yet to see a saw seize down to a blocked fuel filter, it is possible but any repair should be backed up with a pressure/vacumm check and a carb tune when running.

 

I can generally salvage most cylinders as it saves a few hundred on a new cylinder and then fit a new quality non OEM piston.

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Years ago I had either a very early MS660 or an 066 (but believe it was the former) which seized after about 5 hrs use. Due to a change in work patterns this use had occurred over 13 months (ie jobs that I got it for got shifted). I took it back to my dealer who sent offending bits off to Sthil.

 

It came back as a mechanical failure (fuel mix ok etc etc) but parts were NOT replaced under warranty. The dealer though did fit and do all work for free as he could see it was still a new saw. Cant say I want to rush out and buy Stihl in a hurry again. Also had a Sthil brushcutter go.(10 hrs use, bearing in engine went, warranty job though this time)

 

No probs with Husky, Echo, Dolmar etc etc

 

 

MS660 is a cracking saw though, works brill on the Logosol too!

Edited by corylus

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If you only use this saw very occasionally, do you drain out the tank in between? If not, it's quite possible that you're getting fuel degradation - bad fuel can wreck a piston inside one tankfull.

 

I would ask them to show you the damaged piston - if it's scored up then it's wrecked, which will explain why it won't start. It doesn't tell you the root cause though, and since it's done it before I would say they didn't find the cause last time and just cured the symptoms.

 

At this point, I would be looking for air leaks. My 066 died without ever over-revving, so you can't always tell by what it sounded like.

 

If you do only run it occasionally, may be worth considering Aspen as it can be left in the tank indefinitely so you don't have to drain off and waste fuel, or get damage if you forget. The high price per litre is less of an issue if the total consumption is low.

 

Alec

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It is unlikely any muck of any volume would get past the fuel filter and if it did, it would end up in the gauze filter in the pumping section of the carb.

 

@Spud: The service agent had said: "clogged up the Carb filter", which indicates that it was indeed the gauze filter being blocked, which I think could cause the saw to run lean, but it would have virtually no power, so I think it would be unlikely not to be noticed by the operator.

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@Spud: The service agent had said: "clogged up the Carb filter", which indicates that it was indeed the gauze filter being blocked, which I think could cause the saw to run lean, but it would have virtually no power, so I think it would be unlikely not to be noticed by the operator.

 

Don't know what happened to this one - he is reasonably local to me, offered to give him a second opinion but heard no more:confused1:

 

You can take your horse to water...but you can't make it wash your car:lol:

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I thought a heat seizure occurs when you dont allow the motor to warm up - making the piston expand quicker than the cylendair....????? also if it was a heat seizure the barrel would probs be pitted and you wouldnt be able to get the motor to turn ?

 

if your running lean you usually have really good rev responce at low rpm - then it would bog out in higher rpms - plus it would be noticeabley hotter.

 

did you check the plug before you took it in ? would give you a good idea if its running lean or not

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do you know if it has a cast iron head or an ally head?

 

Not being funny but we are talking about a MS660 here - cast iron heads were found on 60s-70s kit like big Danarms, Homelites & old McCullochs etc almost all modern saws are Nikasil plated aluminium:confused1:

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I thought a heat seizure occurs when you dont allow the motor to warm up - making the piston expand quicker than the cylendair....????? also if it was a heat seizure the barrel would probs be pitted and you wouldnt be able to get the motor to turn ?

 

if your running lean you usually have really good rev responce at low rpm - then it would bog out in higher rpms - plus it would be noticeabley hotter.

 

did you check the plug before you took it in ? would give you a good idea if its running lean or not

 

Both the Cylinder and piston are made of aluminium and will share the same expansion characteristics but I am guessing if you took a cold saw to a large piece of wood and went at it for a couple of minutes, you may get a saw that is running on the lean side to seize but the reasons I have mentioned earlier are the prime reasons and most common reasons for a saw to fail.

 

A seized cylinder can be salvaged - if you look at the thread "Whats on your bench tonight" you will see some I have salvaged and have a good success rate on cleaning them.

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