Confused about chain pitch and power

[AmateurSawer]

I have read numerous posts saying that someone who runs a long bar on a small to mid size saw ( say 24" on a Stihl 362 or Husqvarna 562) should use a skip chain for the fewer teeth in the wood not robbing power.
My son had a .325 pitch chain and 20" bar on his 290 ( 81 links ) and changed to a 3/8 pitch (72 links ) because of the readily available 72-72 chain in our area.He switched back because he felt he lost power.
Seems to me that he should have gained power by the above advice.Both chains he used were sharp and non-skip.
What am I missing?

 

[Deleted member 149229]

The chain professor @Philbert

 

[HarleyT]

Do you have a pic of your 72 chain?

 

[nandoz]

First off the smaller diameter sprocket on the .325 setup spins faster. Secondly the number of cutters between the two, doesn't equal the difference between full comp and skip chain. Third consideration is the width of the chains and consequently the width of the kerf.

 

[AmateurSawer]

Forgot to mention.325 chain had .063 guide groove and 3/8 was .050 if it matters.Both were full chisel chains.

 

[Franny K]

I have read numerous posts saying that someone who runs a long bar on a small to mid size saw ( say 24" on a Stihl 362 or Husqvarna 562) should use a skip chain for the fewer teeth in the wood not robbing power.



My son had a .325 pitch chain and 20" bar on his 290 ( 81 links ) and changed to a 3/8 pitch (72 links ) because of the readily available 72-72 chain in our area.He switched back because he felt he lost power.
Seems to me that he should have gain power by the above advice.



What am I missing?

It is unclear if anything is skip beyond the first sentence.
The power should be the same perhaps the performance different.

Perhaps what you are missing is that a 7 tooth sprocket with normal chain brings 7 cutters across a given location every two revolutions. If the .325 cutter is smaller or thinner or sharper or has a more efficient design then to me it would seem to perform better. Yes the 3/8 will have more speed that may effect things as well. How deep the shaving removal is will effect things as well. The ratio is close to 8 to 9 cutters per given length.

 

[nandoz]

Chain gauge applies to the driver but not necessarily the width of the cutter. I might be wrong, somebody chime in if I am. I have .325 .050 b/c that is full width, and .325 .050 that is narrow kerf.

 

[AmateurSawer]

Both were standard chains and not skip.Sorry if I was unclear.

 

[rwoods]

If the drive sprockets have the same number of teeth the .325 will be pulled at a slower speed than the 3/8 thus have more torque - kinda like 1st gear instead of 2nd gear. If the .325 has a narrower kerf then it is cutting less wood so it takes less power to pull.

Ron

 

[Ryan'smilling]

Okay, .325 on a 20" bar will have what, 2 more cutters in the wood with the bar buried? Something like that, anyway. But, look at the teeth. .325 cutters are considerably smaller. They take a smaller narrower bite, which requires less power. Also as Ron said, because the drive sprocket is smaller, you have more available torque with the .325 7 pin.

Just this afternoon I cut a bunch with my ported 261. I was running .325 7 pin on a 16" bar. When it dulled I swapped to a 3/8 7 pin also on a 16" bar. I did that because I have a bunch of dirty wood to buck up and I have some nice semi chisel in that loop size. Also, I prefer filing 3/8, and this wood makes for lots of filing. The 261 pulled it nicely, and there was definitely not chain speed. Not sure which setup actually cut faster, but I know that the .325 offered more torque. It was easier to stall the chain with 3/8.

 

[HarleyT]

I revolution of the sprocket will move 7 teeth, whether it is 3/8 or .325 {7 tooth sprocket}

 

[jakethesnake]

I keep it fairly simple. Up to 50 ish cc engine. I’m personally running .325. Say 55 or so ccs and up. 3/8. The .050 .058 .063 is the bar slot size. Doesn’t affect a whole lot on cutting performance. Just have the right size for the bar

 

[Philbert]

All of the above.

Seriously, the number of teeth, sequencing (skip, etc.), sprocket size, etc., all make a difference.

Going from .325 to 3/8 pitch chain means fewer, but larger, cutters, which he probably noticed (assuming they were sharpened identically).

He could try 3/8 skip; or .325 skip; or .325 narrow kerf chains - each would put a smaller load on the powerhead. But what was wrong with what he was running?

Philbert

 

[rwoods]

I revolution of the sprocket will move 7 teeth, whether it is 3/8 or .325 {7 tooth sprocket}

Yes, but the .325 will move it less distance per revolution. Thus it is cutting less per rev. Think .404 versus 3/8. Takes a lot more torque to pull a .404. Ron

 

[Franny K]

I revolution of the sprocket will move 7 teeth, whether it is 3/8 or .325 {7 tooth sprocket}

The sprocket tooth moves a drive link. There was a discrepancy in one of the Stihl documents you attached lately with the text saying 4 drive links per cutter and the picture showing 3. That being for skip chain. Maybe it said twice as far apart not what I put above. That 81 dl loop will have 20 right and left cutters, If normal. Are you playing games with the above quote or is tooth confusing?

 

[HarleyT]

OK, 7 drive links/tangs.

Good lord. The point is the 7 "tooth" sprocket moves the chain 7 drive links per engine revolution.

Damn.

What Stihl document are you talking about?

 

[HarleyT]

First off the smaller diameter sprocket on the .325 setup spins faster

If the drive sprockets have the same number of teeth the .325 will be pulled at a slower speed than the 3/8 thus have more torque - kinda like 1st gear instead of 2nd gear.

 

[Cliff R]

It's all about the .325" chain vs 3/8" more than anything else.

For my saws here I run .325" on my 50-55cc saws and no more than an 18" bar. For the smaller saws they are all 3/8LP with 14" bars. For 60cc and larger saws I run 3/8" and only run skip tooth on the longer 28" and 30" bars.

I've determined over decades of cutting wood that 3/8" non skip tooth, especially full chisel requires at least 60cc to effectively power it. Case in point, they made 55 Rancher saws with 3/8" 20 bars, which is WAY too much for the cc and open port P/C design. They would be OK for casual use around the farm or house, but we cut a LOT of wood, usually tops left over from logging operations and that deal just doesn't cut it. Instead we outfit all our 50-55cc saws with 18" .325" set-ups which greatly improves cutting performance.

I have found that an 18" 3/8" set-up to be best on the 262XP, the 268XP gets 3/8" and 20" bar. The CS-590 Echo runs 3/8" 20", the 600P 3/8" 24", and the 480CD 30" 3/8" skip tooth. I'd add here that the 268XP is also outfitted at times with a 24" bar 3/8" full chisel and fine with it.

Since we heat 3 homes for decades now we cut a LOT of wood, and in recent years with all the Ash trees dying out even more than in previous years. No time to mess around with saws that are under-powered or have too much bar/chain on them for the cc's. I take no less than 3 saws on any outing, usually 4-5 and as each one runs out of fuel or gets dull just grab another one and keep on getting it done.

I'd also add here than past 18" .325" just doesn't cut it anyhow, same with 3/8"LP past 16". Difficult to explain why but as you increase bar length and number of links the integrity of the bigger chains just flat work better with the longer bars, at least if you do a lot of this sort of thing.....FWIW......Cliff

 

[Ted Jenkins]

The factory matched the best chain to the power. The above points are true. The wider the cutters, the more teeth per inch or foot, high profile vs, low profile will all take more power to pull a chain through a log because a bigger wider cut is being performed. A skip tooth chain has fewer cutters enabling a certain motor to pull that chain when it is on a 48'' bar vs. the same motor pulling a chain with a normally used 32'' bar. If you want to get the job done get a motor to do so. My limbing saws start at 60 CC and then to 110 CC. Just pull the trigger and watch the chips fly. Get some saws and do not get frustrated. Thanks

 

[J.W Younger]

I revolution of the sprocket will move 7 teeth, whether it is 3/8 or .325 {7 tooth sprocket}

7 drive links per rev