overrevving ???

Button · December 17, 2005, 06:50:01 AM

A freind was cutting cordwood when he put his saw down to drag some brush. After about a minute the saw stopped running. He thought it had run out of gas. When he pulled on the cord the saw was locked up. He brought to the shop and they said the piston and cyl were scored from overrevving. The saw is just over a year old and not under warranty. He has always mixed his gas 50:1 but also adds a half bottle of dry gas to 5 gallons of mixed fuel. Could this have been it ? He has never had a problem otherwise and never adjusted the mixture screws since they did it at the shop when new. Not sure of the model but it is stihl and cost him 900. Thanks , enjoy the day.
Peter

mike_van · December 17, 2005, 06:59:12 AM

I've never put dry gas in 2 cy. mix, I also run 32/1 mix in everything I own. Never siezed an engine that way. I have fixed a lot of them that have, it's not always necessary to replace the piston, ring & jug, sometimes you can clean it all up, lightly hone the cylinder & be running again.

Kevin · December 17, 2005, 10:13:03 AM

He shouldn't need dry gas and 40:1 would be a better mix.

Rocky_J · December 17, 2005, 11:56:19 AM

That alcohol he added to the fuel was the culprit I betcha. And like others have said, 50-1 is the absolute end of the 'safe' mixture scale. I run 40-1 and have all my saws tuned to run on that mixture.

macpower · December 17, 2005, 01:39:11 PM

I've seen a lot of this. Small engines do not like alcohol/dry gas. Two strokes will not tolerate it at all. If you think you have water in your gas, get rid of it and get fresh gas.
The dry gas would have ruled out a warranty claim even if the saw was new. Stay with what the manufacturer recomends for gas oil mix and leave the additives out.

Tony_T · December 22, 2005, 08:01:40 PM

I learned this one the hard way.

Noticed a bit of water in my mix and added isopropanol dry gas as it was winter and was worried about icing up. Less than the next tank full later, my previously sweet running Stihl 028 super had a scored piston and peeled chrome bore. 2 strokes do not like dry gas/alcohol

With a new cyl/piston assy the same saw is still going stong after wearing out many chains , and a few bars using the same mix (minus the dry gas).

PKAMWood · January 25, 2006, 05:47:21 PM

Yeah, I know this is an old thread, but the same thing happened to my Sthil MS660 in October.

It's called a "high speed sieze" and it happens because of CARB (not the carb, the government one).

In CT they play by California's emissions rules. Even for saws. To make the emissions mandate they tune them lean at the factory.

Unfortunately, when the saw starts to break in (around 5 hours) the saw starts to run lean (as the saw loosens up it gets leaner). My shop usually richens them up a quarter turn (or was that a half turn?) before delivering them. They didn't do that with my saw and it siezed at a cutting job an hour away (*DanG glad I had two saws).

The dealer, being an excellent shop to deal with, got Stihl to cover the cost of the jug kit and the shop covered the labor. Needless to say, I recommend them whenever I get a chance!

They'll let you do *anything* in Canterbury except put a manure trailer in the town hall parking lot :D

WoodSmith · January 25, 2006, 09:08:29 PM

Why all of a sudden are we hearing from factory authorized dealers and saw shops to run 50:1 (is this due to tighter emission regulations or are the newer motors capable of long engine life with 50:1?
I've been running 2 cycle motors ie; power hand tools, motorcycles, for years and I have never ever heard about putting alcohol or dryer in the fuel and I live in one of the wettest parts of the globe?
Inquiring minds want to know? ???

StihlDoc · January 25, 2006, 10:15:06 PM

Many manufacturers have been recommending a 50:1 fuel/oil ratio for 10-15 years. The lubricity of the oils have improved and the engine manufacturers were experiencing too much combustion deposit build-up and ring sticking at the richer 40:1, 32:1, etc. ratios. The exhaust "chemicals" that EPA is regulating has little to do with oil or mix ratios and 50:1 has been in effect long before legislation mandated lower exhaust emissions from small engines.

"Dry gas" or "Heet" is for use in auto engines at below freezing temps to keep any residual water in the gas tank and fuel lines from turning to ice and blocking fuel flow. The alcohol mixes with the water to lower the freezing point and also helps suspend the water in a combustible fuel so it passes through the engine without misfiring or stalling the engine.

fishhuntcutwood · January 26, 2006, 02:03:50 PM

So yeah, the dry gas may have been the direct culprit, but saying that the saw is a year old with no carb adjustments sure as heck didn't help things either. I adjust my carbs often due to elevation, temp and season changes.

Jeff

tony_marks · January 27, 2006, 05:34:00 PM

this type problem is why u need a good dealer to educate u on use. also never take a chance on 2 cycle engines . if u dont know its ok ,dont do it.
heet etc.some read a little on carb adjusting and immediatly start doing it themselves. i suspect this has been the undoing of many 2cycle motors.im guilty of this myself.
as for 50-1 mix. it works fine on trimmer motors etc[altho i know from experience, they wear out quicker.]but a saw cutting thru hardwood is gonna be ask for a lot more than a trimmer.turning an trimmer string.
i use mobile synthetic at 32-1. since i started doing this ,ive had little problem with engine failure.
not claiming to be an authority ,just my experience,with 2 cycles

stihltech · January 29, 2006, 06:48:47 PM

Also remember, a drop of drygas is more than enough in a chainsaw gastank. The best way to make sure you don't have water in the fuel is to pour it into a glass jar. The water will always settle to the bottom.

Pour off the fuel, but leave the water in the jar and dispose of it.

50 to 1 in a work saw isn't the problem, dirt and contaminated fuel is.

Bill · February 01, 2006, 12:31:28 AM

Question for those that may know -

With all the talk about alcohol in the fuel - here in SE Pa they put ethanol ( i think I got that right ) in the gas for winter. The question is did I hear right that don't put ethanol in premium ?

My thinking is that the ethanol would be just as bad as dry gas w/alcohol .

Thanks for any answers . . .

StihlDoc · February 01, 2006, 08:42:51 PM

Ethanol fuel has no more than a 10% blend of alcohol in the fuel. This amount does not cause a problem as long as your carburetor adjustments are correct for the fuel. You may have to slightly richen the fuel mixture adjustment screws by 1/16 to 1/8 turn. Premium fuel can also contain ethanol. The filling station pumps will be labeled as such.

Minnesota_boy · February 02, 2006, 09:01:22 AM

Quote from: StihlDoc on February 01, 2006, 08:42:51 PM
Ethanol fuel has no more than a 10% blend of alcohol in the fuel. This amount does not cause a problem as long as your carburetor adjustments are correct for the fuel. You may have to slightly richen the fuel mixture adjustment screws by 1/16 to 1/8 turn. Premium fuel can also contain ethanol. The filling station pumps will be labeled as such.

My state is pushing to increase the amount of ethanol in gasoline to 20%. My Stihl has fixed jets in the carb. Now what? :'(