Backward running Stihl !?!?

[nytreeman]

I have an old Stihl 051 AV running a 36" bar it's an old saw but she's always been a beast and still has lots of power.But last couple of times I used it it after it got hot it would give a little backfire just a little burp really,while cutting,running wide open,and start running backwards.Is this a timing issue or what?? I havent touched the ignition or done any work on it at all just seemed strange it would start doing this. Any suggestions?

 

[rreidnauer]

Not sure if this is a joke, but OK, I'll bite.

Sheared flywheel key threw out the timing?

 

[nytreeman]

No joke,the first time it happened I was cutting a big white pine and I thought I had hit something in the trunk and wiped out the chain.Shut it off to see the damage and the chain was fine,started cutting again ,cut fine for awhile and then a little pop and it did it again.Looked down and this time I saw that the chain was running backwards and since then its done it several times,and no the key and flywheel seem fine.

 

[Cedarkerf]

Had an 064 crank bearing worn so bad that fly wheel smaked ignition module and caused it to run backward.Knocked the timing out of wack.

 

[GASoline71]

Seen that happen on an older 066 once too.

Gary

 

[Sprig]

Flip da chain around an' keep goin'!






(its a joke man, a joke!)

I think the shear-key onna flywheel suggetion makes the most sense, something is very out of whack and I'd be finding out what exactly it is before running it again either hurting the saw, or worse, you.

My very tired 0.02$ worth, and I dunno 'cause I've only heard of this and never had ta deal with it, bizzarre imho, just tain't right man!

And keep us posted eh


Serge

 

[Lakeside53]

It happens on the old saws... find out why the igntion is advanced and you'll have you answer. Flywheel key is a good place to start.

 

[ropensaddle]

I though all stihls were bachwards lol . just kiddin that would be
kinda scary get er fixed and go back to work!

 

[Patrick62]

This don't make no sense

To quote:

"it would give a little backfire just a little burp really,while cutting,running wide open,and start running backwards."

Will someone please explain to me how a saw running wide open, in a cut can come to a complete standstill from something like 7000 rpm??
Then "Burp" and take off at 7000 something rpm the opposite direction???

This don't make sense. I have heard that upon starting a saw, the old timers with points mostly, could back pop and start running reversed. If the ignition is set pretty close to TDC the power would be about the same, and run just dandy backwards.

Objects in motion tend to remain in motion unless acted upon by another force. This applies to anything that moves, including but not limited to flywheels, bullets, and planets.:jester:

-Pat

 

[Lakeside53]

It usually (but rarely) happens in the cut, but I assume the "burp"/backfire stopped the motor, spun it in reverse, and it keep on going... There's been discussion on 064's doing this , so maybe an AS search would turn it up.

Modern ignitions make sure of the direction and have a minimum RPM before firing.

 

[stihltech]

bassackwards

Usually hasthe moduleunder the flywheel if electronic, or the point timing is off. Pays to time with a dial indicator through the plug hole.

 

[Stumpcutter1]

So I'm not crazy

Had the very same thing happen to me a couple weeks ago cutting a stump off with my 045 but the saw backfired and stalled and when I restarted it it ran backwards,told my partner and he said I was nuts he started it up and it ran fine(of course).But sofar my saw only has done it after it stalled

 

[lesorubcheek]

I have an RC airplane engine that'll do it from time to time. Situation is a bit different since its basically a glow plug with no timed ignition. Some of the Homelite info I've read mentions design on their electonic ignitions to prevent firing if rotating in reverse direction. Without some limiting mechanism its very probable a 2-stroke saw would run in reverse, even though its timing wouldn't be as designed.

Dan

 

[Cedarkerf]

To quote:

"it would give a little backfire just a little burp really,while cutting,running wide open,and start running backwards."

Will someone please explain to me how a saw running wide open, in a cut can come to a complete standstill from something like 7000 rpm??
Then "Burp" and take off at 7000 something rpm the opposite direction???

This don't make sense. I have heard that upon starting a saw, the old timers with points mostly, could back pop and start running reversed. If the ignition is set pretty close to TDC the power would be about the same, and run just dandy backwards.

Objects in motion tend to remain in motion unless acted upon by another force. This applies to anything that moves, including but not limited to flywheels, bullets, and planets.:jester:

-Pat

I actually have the event on video were my 64 did it it burbled and grunted then went. Its a large file ill see if I can edit it down.

 

[nytreeman]

I actually have the event on video were my 64 did it it burbled and grunted then went. Its a large file ill see if I can edit it down.

were you able to get that video?I'm going to try to take one of this tomorrow when my wife is home,probably wont do it then

 

[Grace Tree]

Back in the 60s I used to flattrack 2 strokes. We'd replace the magneto flywheel with a lighter machined steel plate and run total loss ignition off the battery. If you were sitting at the start line and let the revs go too low it would burp and run backwards. The trouble was that with the starting line noise you wouldn't know it until the flag was dropped and 9 bikes went forward and you went backward. It happened to me a couple times and it was pretty embarrassing. I think the Germans had a 2 stroke boat that used to run the motor backwards for reverse.
Phil

 

[nytreeman]

Where can i find the specs timing,etc. for this old 051? prob mid-late 70's with electronic ignition?

 

[Patrick62]

I get it, I think

So the engine is losing rpm for some reason, ignition goes bonkers, carb get's sucked dry, whatever... and then in it's last throws it regains fuel, spark and fires prematurly causing it to take off in reverse.

I was having problems with the mechanics of motion doing a reversal in 1/100 of a second. Flywheel, clutch, chain, everything all of a sudden!!! we go the otherway around. Oh, and do it so smoothly that the operator has no clue as to WTF happened.

The cool part is that most oil pumps would continue to lube the bar. In fact the only thing that would not work properly would be the fan!

-Pat

 

[RaisedByWolves]

Back in the 60s I used to flattrack 2 strokes. We'd replace the magneto flywheel with a lighter machined steel plate and run total loss ignition off the battery. If you were sitting at the start line and let the revs go too low it would burp and run backwards. The trouble was that with the starting line noise you wouldn't know it until the flag was dropped and 9 bikes went forward and you went backward. It happened to me a couple times and it was pretty embarrassing. I think the Germans had a 2 stroke boat that used to run the motor backwards for reverse.
Phil

I seen this happen to a Ossa Trials bike.


The guy hit a rock wrong and went backwards off of it and the motor started running backwards.



He was able to go 10-15' in reverse before loosing his balance.



.

 

[ciscoguy01]

Hmmm

That's gotta be a first on that dude... However, I'm thinkin' if you sharpen both sides of the chain, you could keep right on a cuttin'... Rock on dude... opcorn:

Let us know what you find eh?