066 Magnum Cylinder & Piston

[fsji4k]

Hello Everyone. I need someone to shead some light on my problem here... I recently bought a Stihl 066 Magnum in Apr 02 and i have already had to return it to the dealer twice for repairs.

Problem is the piston is running so hot that the compression rings are being melted right to the piston and the piston is scored. The scoring is only at the exhaust point in the front. The back of the piston (oppisite side of the exhaust) is perfect.

The first time it quit I had about 20hrs on it. The second I had about 30 minutes use before it quit....with the exact same problem.

Could anyone let me know what might be causing this and if this might be a common problem? Thanks a lot!

-066 magnum 28" bar
-mixture 50:1 (Stihl Oil) / high octan gas
-original setup has never been changed
-..and no i haven't lent it out...LOL!

 

[HUSKYMAN]

Either the carb is messed up, the jets are set wayyy too lean, or there could be a leak in the boot from the carb to the crankcase.

Also there could be a crank seal leaking or a crack in the crankcase itself

You need to get this worked out before the warranty expires

 

[fsji4k]

The dealer has been quite helpful thankfully, but yes i'm glad it's under warranty.

My thought was there has to be a crack and air is getting in making the mixture too thin hence causing the problem...just a thought.

Thanks for the quick reply...

 

[timberwolf]

I think one of the Guys on the site (Timber turner had simmilar problems, I think it ended up as carb/jet problems. check out the threads he posted.

Not sure if your muffler is opened up yet, but once you get things in order, it would help to reduce tempratures, and improve power.

I'm mixing 40:1 on my saws to offer a bit more oil, no problems so far.

Good luck, glad your dealer is looking after you well.

Timberwolf

 

[JimL]

you using pump gas? I only run 87, 92 burns too hot.
got 6 066's i run this in and have zero problems.

 

[bwalker]

I only run 87, 92 burns too hot.

Since all three grades of gasoline have virtually the same BTU content 92 Burns no hotter than 87 and vice versa. Many people are hung up on the idea of octanes influance on burn temp, but provided the engine is not detonating or pre igniting there is no differance in burn temp.

 

[HUSKYMAN]

Actually 87 would burn hotter than 92, since 92 has a higher ignition point and higher octane burns slightly "slower" than lower octane

 

[fsji4k]

Thanks Timberwolf. I searched for the thread by timberturner and found the exact problem i was having. for those interested or might be experiencing this problem, here's the thread:

http://www.arboristsite.com/showthread.php?s=&threadid=5738&highlight=ill+be+darned

 

[bwalker]

Actually 87 would burn hotter than 92, since 92 has a higher ignition point and higher octane burns slightly "slower" than lower octane

The octane rateing is a fuels resistance to detonation, not ignition. The two are very differant.Higher octane does not burn slower and does not burn cooler.

 

[JimL]

I switched to 92 in just one of my 066's, had the muffler opened up for some time on it.

I ran it for about 3 days and the piston and rings melted. I am not one to argue about something, this is proof enough for me. I checked RPM's after running half tank through, no change....


Not sure why but there had to have been more heat.

 

[HUSKYMAN]

Originally posted by bwalker
The octane rateing is a fuels resistance to detonation, not ignition. The two are very differant.Higher octane does not burn slower and does not burn cooler.

Here we go again walker, dont turn this into another octane fight. It takes more to ignite higher octane fuel, and in an internal combustion engine it can result in lower combustion temperatures. Get an EGT gauge one time and take a look.
This thread is not about octane, lets not turn it into one

 

[bwalker]

It takes more to ignite higher octane fuel,

NO it does not.

 

[treeclimber165]

The quicker you open up the muffler, the sooner you will reduce head temps by 50*. Most people insist on waiting until after 'break-in' before modifying the muffler. This makes no sense. Open up the muffler as soon as possible to minimize additional heat damage. It might be too late, though, for your saw. Sounds like plenty of damage has been done.

See if they will swap out your saw for a new one that hasn't been overheated. Even if it costs you a little more money, you would be better off in the long run. They cannot eliminate the heat damage already done.

 

[bwalker]

Climber, I agree with you on not waiting to open up the muffler after breakin. In this case though I doubt the epa muffler is the cause of the failures. Something is not right with this saw as others have mentioned(airleaks,lean,etc).

 

[Jacob J.]

Howdy-

We have a refinery ( Shell & 76 ) here locally and I've been told that the higher octane gas burns slower and scavenges cleaner, so even though the ignition temperature has to be higher for higher octane gas to burn, the scavenging ability of the higher octane actually runs an engine cooler. Is there any truth to this?

 

[Dieselnut]

outch,
I posted once, but it didn't go right...I am not an expert by no means, but I don't think the saw would suck fuel right if there was an air leak between the carb and the cyl. I did however see a poulan do this because of a inprouper air vent in the gas cap of the fuel tank...Was a odd ball kind of thing, but it did do it... That was something that took a long time to figure out.

 

[tundraotto]

airleak, airleak, airleak.

Since your saw is under warranty you should get your saw fixed right ASAP!! Stihl requires their dealers to perform a vacuum AND a pressure test on all saws that are being fixed for a lean running condition, which yours sounds like it is. Make sure your dealer does what he is supposed to do.

 

[stihltech]

vent

Airleak, definitely. Also check out tank vent, have seen some sticky ones lately. Track that lean condition to the end or it will never be right. I might also push for another unit, that much lean sieze just isn't right for a new saw.

 

[bwalker]

Is there any truth to this?

None what so ever.

[

I ran it for about 3 days and the piston and rings melted. I am not one to argue about something, this is proof enough for me. I checked RPM's after running half

So if I ran adifferent brand of diesel in my truck and it melted a piston would I assume the fuel was the cause?

 

[JimL]

Originally posted by bwalker
None what so ever.

[
So if I ran adifferent brand of diesel in my truck and it melted a piston would I assume the fuel was the cause?

Might, not sure but I had always used the same gas from the same gas station, always.

I run my saws hard every day. I would know it if there was a change in performance.