No power when cutting with top of bar

asgeist · Jan 28, 2013

All,

I'm having a strange problem with my Husky 345. The engine runs fine, chain oiler working fine, power and speed of cut is fine, so long as I'm cutting with the bottom of the bar. But when I cut with the top of the bar, as you might when finishing a cut with both ends of the log supported, cutting in the middle, and top cut begins to pinch, it has very little power. Even with a branch as little as a few inches, if I apply any up pressure, there's just no oomph. Any ideas?

A Geist

Fifelaker · Jan 28, 2013

Check the top of your bar for wear.

Philbert · Jan 28, 2013

What's the nose sprocket on your bar look like?

When you cut on the bottom of the bar, chain tension is maximum between the wood and the drive sprocket (which pulls the chain) - the rest of the chain gets a 'free ride' over the top and around the nose.

When you cut on the top of the bar, maximum tension is pulled from the wood, around the nose, across the bottom of the bar, all the way to the sprocket.

So if your nose sprocket is worn to the point where the tie straps are riding on the bar rails at the nose, instead of being held slightly off by the sprocket (and bearings inside), you will get increased friction and less cutting power. Illustration below from the Oregon Maintenance and Safety Manual.

Other than that, gravity?, magnetic north?, curvature of the earth?, . . . .?

Philbert

Naked Arborist · Jan 28, 2013

Sounds like you fuel filter is hung up or the line broke in the tank. Check it.

Dan_IN_MN · Jan 28, 2013

Like others said, might be a warn bar. How long have you had the saw? How old is the bar? Have you flipped the bar over?

Oh, Welcome to the AS forum!

millbilly · Jan 28, 2013

I can't rember what make saw I was using at the time, might have been a husky, just not sure. Anyway the motor mounts were worn, and when I cut with the top of the rail, it would actually close the throttle some and I would lose power.

awful knawful · Jan 28, 2013

millbilly said:
I can't rember what make saw I was using at the time, might have been a husky, just not sure. Anyway the motor mounts were worn, and when I cut with the top of the rail, it would actually close the throttle some and I would lose power.

my 268XP had the same problem.

Dan_IN_MN · Jan 28, 2013

millbilly said:
I can't rember what make saw I was using at the time, might have been a husky, just not sure. Anyway the motor mounts were worn, and when I cut with the top of the rail, it would actually close the throttle some and I would lose power.

Could you hear the drop in the throttle? How did you figure it out?

northmanlogging · Jan 28, 2013

rakers not set right... (depth gauges whatever...) or a wonky tip on yer bar, just tossing stuff out there and seeing what sticks?

bucknfeller · Jan 28, 2013

Chain tension too tight can do it. Like someone said earlier, on the down cut it's tightest between the wood and the sprocket, if it's too tight to begin with, when your on the up cut it can be extremely tight over the nose.

fearofpavement · Jan 28, 2013

If you don't have another bar and chain for this saw, see if you can borrow one to test with. That will be the easiest way to determine if it is the powerhead or the bar/chain. When you make that determination it will be easier to seek a proper solution.

Lignator · Jan 28, 2013

post a pic of nose of the the bar / chain. would help determine if sprocket is worn out as we could see the clearance.

TonyRumore · Jan 28, 2013

You just need to turn the entire saw upside down when making that cut. That way, you're always cutting on the bottom of the bar....thats why they make full wrap handles. Everyone knows that.

stihlavarna · Jan 29, 2013

When it happened to me, mine was loose on the studs pulling the bar down and tightening the chain.

WidowMaker1 · Jan 29, 2013

asgeist said:
if I apply any up pressure, there's just no oomph. Any ideas?

Go 6 cube

galde · Jan 29, 2013

Philbert said:
What's the nose sprocket on your bar look like?

When you cut on the bottom of the bar, chain tension is maximum between the wood and the drive sprocket (which pulls the chain) - the rest of the chain gets a 'free ride' over the top and around the nose.

When you cut on the top of the bar, maximum tension is pulled from the wood, around the nose, across the bottom of the bar, all the way to the sprocket.

So if your nose sprocket is worn to the point where the tie straps are riding on the bar rails at the nose, instead of being held slightly off by the sprocket (and bearings inside), you will get increased friction and less cutting power. Illustration below from the Oregon Maintenance and Safety Manual.

Other than that, gravity?, magnetic north?, curvature of the earth?, . . . .?

Philbert

Nose sprocket spur wear occurs mostly on the spur points that protrude outside of the rails. The tie straps start to wear on the nose rails when the drive links lose depth, mostly due to being run loose, which causes the drive sprocket to pound off the tips of the drive links.
EDIT: If the bearings in the nose are worn the spur can shift enough to let the tie straps rub the rails. The cheapo skinny bars that come on low-end lo-pro saws have weak bearings that have short lifetimes. If there is substantial fore-and-aft play in the nose spur, then it is shot.

Erock · Jan 29, 2013

millbilly said:
I can't rember what make saw I was using at the time, might have been a husky, just not sure. Anyway the motor mounts were worn, and when I cut with the top of the rail, it would actually close the throttle some and I would lose power.

My bet is either this or a cracked impulse line or intake boot that only opens up when you put pressure on the top of the bar. I know someone had an issue like this a while back and it was one of the two (impulse or intake boot)

millbilly · Jan 29, 2013

Erock said:
My bet is either this or a cracked impulse line or intake boot that only opens up when you put pressure on the top of the bar. I know someone had an issue like this a while back and it was one of the two (impulse or intake boot)

I think you hit the nail on the head, I never even looked for that. I just knew it was due to movement in that area. Thankyou.

tallfarmboy · Jan 29, 2013

Erock said:
My bet is either this or a cracked impulse line or intake boot that only opens up when you put pressure on the top of the bar. I know someone had an issue like this a while back and it was one of the two (impulse or intake boot)

Winner, winner, chicken dinner... Flexing the saw opens up a cracked intake boot or impulse line. My guess is intake boot.

Good luck!
TFB

milkman · Jan 29, 2013

My bet would be with the last three posts, first thing I thought of because I heard it mentioned in another thread that worn AV mounts could affect the intake boot.

No power when cutting with top of bar

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