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Dolmar running backward?

Started by Faron, July 22, 2007, 04:43:17 AM

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Faron

Yesterday a customer and I were quartering a red oak with my chainsaw, a Dolmar 116si.  He kind of stalled the chain, almost  killing the engine. When he revved the saw back up, the saw was running backwards. It sounded ok, just running in reverse. We shut it off and restarted it, and everything seemed fine.  Later in the afternoon, the same thing happened again.  This time we put that saw up.  My friend is kind of bad about letting the saw dog down while he is rippng.  The question is, is there a mechanical problem with this saw, or is this a result of his sawing technique?  He has to be actually killing the saw, and then it rebounds in reverse and restarts.  At least that is the only way I can see it happening.  Any ideas?
Democracy is two wolves and a lamb voting on what to have for dinner.  Liberty is a well armed lamb contesting the vote. - Ben Franklin

ladylake

Maybe the flywheel key is sheared a little or the coil mounts loose.  Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

sawguy21

What Steve said. The ignition timing is too close to TDC and the engine is bogging down and 'kicks back' against compression.
old age and treachery will always overcome youth and enthusiasm

Faron

Thanks, guys.  I will get it to the shop next week.  It kind of makes you doubt your eyes when you see it.  :o
Democracy is two wolves and a lamb voting on what to have for dinner.  Liberty is a well armed lamb contesting the vote. - Ben Franklin

barbender

The old detroit diesels, which were two stroke, would do that if you lugged them down. Just about the time you would push the clutch in she would fire back up, you'd let out the clutch and you'd be going backwards. They wouldn't rev up when they ran backwards, either. As far as saws I've never seen that before. You might have to sharpen both sides of the saw teeth to keep it productive :)
Too many irons in the fire

sawguy21

 :D That was also how some of the old railroad section gang 'speeders' shifted from forward to reverse and back.
old age and treachery will always overcome youth and enthusiasm

Faron

A fellow was telling me that about the Detroits yesterday.  He also said they were burning crankcase  oil instead of desiel when they ran backwards.
Democracy is two wolves and a lamb voting on what to have for dinner.  Liberty is a well armed lamb contesting the vote. - Ben Franklin

Ianab

If it bogs down enough to kick backwards then check the clutch is disengaging at idle. When it bogs down enough the clutch should slip. Broken / stretched springs in the clutch?

Ian
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

beenthere

Someone else wouldn't be running my chainsaw, even less, like that.....

To me, one cuts the most wood keeping the rpm up and the clutch engaged.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

submarinesailor

Once upon at time, I was on the back of a diesel fire truck that started backwards.  It was an old air start Detroit Diesel that started backwards about 1 in 100 times.  First time it happened, I was on the back – way back when you could ride on the back. 

The back wall of the fire house coming at you was good incentive to get off real quick. ;D

Bruce

Al_Smith

Unfortunately when to old Detroits fired backwards,in short order the blower would suck the lube oil out of the engine and make one mell of a hess.In the days of two cycle go karts,on occasion one would fire up backwards.If they were running twin engines without a live axle,these things would "zero turn" about like a bulldozer,not too handy at all.

sawguy21

 :D :D That would get entertaining in a hurry.
old age and treachery will always overcome youth and enthusiasm

Al_Smith

 I myself am an ex uboat sailor also.I have never seen this but have heard of the big "Jimmy diesels" that for some unknown reasons fire up backwards.Needless to say that would make an awfull mess.

I've also heard of "run aways" where the big diesel was burning it's own lube oil as fuel and became a problem to shut down.That's a bit off topic.

Oh,before I forget,another go kart story.Years ago,early 60's,some ran the karts direct drive,no clutch.They often used "scrubber" brakes which used a friction plate against the tire which was slightly better than dragging your feet.Then along came "Airheart" disc brakes,borrowed from the aircraft design.These would stop you on a dime and give you 9 cents change.

Often times however,this positive braking stalled the direct drive Mac  and US 820 engines.If they spun around on a dirt track,usually nothing happened,just dead in the water,so to speak.If however they spun it on an asphualt track they some times fired backwards and that was a sight to behold. :D

WAGZ

most of the newer ski doo's are made to do that for reverse.......kinda a neat idea.....you put it in "R" and then the machine shuts itself off, then starts back up in reverse.....
I'd do the same for somebody I liked !!

Furby

I was told golf cart engines do that, but can't seem to find ANY info at all on them.
Anyone have any links or other info?

Al_Smith

Try googling EZ Go.Harley -Davison made reversing two cycle golf carts as well,perhaps Cushman also.

gumnut

Yes, my old grandad used to tell a terrificaly funny ripping yarn about an old truck that fired up backwards, and chernobled the air filter, and created all sorts of havoc careering around the yard.
But all the big two stoke ships engines I work on are direct reversing, albeit with a reversing arrangement on the camshaft.

sawguy21

A four stroke will should not run backwards because of the valve timing unless it has a 'marine' or reverse grind cam installed.
old age and treachery will always overcome youth and enthusiasm

Al_Smith

Quite a few marine diesels were reversable.On a humerous note I recall reading about a river tow boat that had  problems on a regular bassis with an oiling system on  the engine.Come to find out the previous owner had installed a counter rotating screw and were running the big Cooper-Bessimer in reverse.The engine was so old they had to contact a retired engineer from the company to figure out the problem.

Striker

The I-H DT466 in our tree truck will reverse if you forget to put the tranny in neutral when you engage the pto.

Jeff

XLIV

Once had a snowmobile do that back in the late 60's (maybe thats where they got the idea to make them do it on purpose..)

The golf carts had a combo starter/generator. They would run in either direction.

44

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