Confused about chain pitch and power

[lambs]

I am currently running 3/8” pitch 16 inch bar on my MS 261. It is definitely slower than 16” .325 bar and chain in 16” or greater wood. But I run it anyway because there’s more tooth to work with. More sharpenings before the chain is shot. And if you’re cutting smaller stuff I think there’s little difference.

 

[HarleyT]

I am currently running 3/8” pitch 16 inch bar on my MS 261. It is definitely slower than 16” .325 bar and chain in 16” or greater wood. But I run it anyway because there’s more tooth to work with. More sharpenings before the chain is shot. And if you’re cutting smaller stuff I think there’s little difference.

Did you run the 8 tooth sprocket when you ran the .325?

 

[Franny K]

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?

section 3.9.9

 

[Philbert]

(Did we scare away another OP yet?)

Some people seem to have an inferiority complex about .325 chain; like it is not 'real' chain. Or they want to run the same pitch chain on all their saws, even if they use different loop lengths.

I periodically go back to the tire analogy: car makers try to match the best size tire for a particular car (including engine size and transmission). Yeah, if is often possible to mount different size tires/rims, but they may not perform as well.

One part of the OP's question referred to skip tooth chain being used to 'extend' the length of bar that a certain powerhead can pull. It also asked about 'power'.

Another factor to consider is the smoothness of the cut. Especially when cutting smaller diameter wood, more teeth (e.g. .325 over 3/8 pitch chain) will cut smoother. On pole saws, typically cutting smaller diameter limbs / branches, the 'dreaded' bumper tie strap low-kickback chains will cut even smoother, by filling in the spaces between cutters.

So, will the saw primarily be used with bars longer than intended by the manufacturer? Primarily for limbing / small stuff? Or a mix of wood types and sizes. In any case, keep the cutters sharp.

Philbert

 

[Marshy]

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.

This is false. At the same engine engine rpm the 3/8 chain will spin faster because the sprocket is larger.

Assume your saw is running at 10,000 RPM in the cut with a 7 pin drive sprocket.

The 0.325 pitch chain will spin 31.6 ft/sec.

0.325"x7x10,000=22,750 inches per min
22,750 in/min ÷ 12 in/ft = 1895 ft per min
1895 ft/min ÷ 60 sec/min = 31.6 ft/sec

The 3/8 pitch chain will spin 36.45 ft/sec.

0.375"x7x10,000=26,250 inches per min
26,250 in/min ÷ 12 in/ft = 2187.5 ft/min
2187.5 ft/min ÷ 60 sec/min = 36.45 ft/sec

So why did I do all that math? Well, proof is in the numbers but it's easy to see that the engine will have to work harder to maintain the same engine rpm because it's doing more work.

As mentioned by others, the 3/8 chain cutter is wider also so there more work there also. Add all that up and put it on an underpowered saw and it could cut like crap.

The way around this is running a less aggressive filed 3/8 chain. You can file your chain to the saws ability and if you take a saws that is a little under powered for 3/8 chain and file it properly it will perform reasonable.

 

[Franny K]

(Did we scare away another OP yet?)

...

I periodically go back to the tire analogy: car makers try to match the best size tire for a particular car (including engine size and transmission). Yeah, if is often possible to mount different size tires/rims, but they may not perform as well.


On pole saws, typically cutting smaller diameter limbs / branches, the 'dreaded' bumper tie strap low-kickback chains will cut even smoother, by filling in the spaces between cutters.



Philbert

He checked in at 9:18 am. Kind of frustrating these things get so much attention compared to the electric stuff.

I just looked you still can get that 90 sg bumper tie strap. The problem is lowering those safety things and staying smooth. I know you have a grinder.

I bought a new pick up truck a two wheel drive one. Put snow tires on the back within 50 miles, I go off road at times. Used the original rear ones on the front later on.

 

[Franny K]

This is false. At the same engine engine rpm the 3/8 chain will spin faster because the sprocket is larger.

Assume your saw is running at 10,000 RPM in the cut with a 7 pin drive sprocket.

The 0.325 pitch chain will spin 31.6 ft/sec.

0.325"x7x10,000=22,750 inches per min
22,750 in/min ÷ 12 in/ft = 1895 ft per min
1895 ft/min ÷ 60 sec/min = 31.6 ft/sec

The 3/8 pitch chain will spin 36.45 ft/sec.

0.375"x7x10,000=26,250 inches per min
26,250 in/min ÷ 12 in/ft = 2187.5 ft/min
2187.5 ft/min ÷ 60 sec/min = 36.45 ft/sec

So why did I do all that math? Well, proof is in the numbers but it's easy to see that the engine will have to work harder to maintain the same engine rpm because it's doing more work.

As mentioned by others, the 3/8 chain cutter is wider also so there more work there also. Add all that up and put it on an underpowered saw and it could cut like crap.

The way around this is running a less aggressive filed 3/8 chain. You can file your chain to the saws ability and if you take a saws that is a little under powered for 3/8 chain and file it properly it will perform reasonable.

1640 drive links per 100 feet. 3/8 is generic if you want to do the math do it right.

 

[J.W Younger]

The .325 chain doesn't seem to be much if any narrower than .375 but is shorter.
My 5100 50cc saw will cut a cookie faster with the 64 dl 3/8 chain it came with but bogs less and is smoother with
a 72 dl .325 using 7 pin rims for real world situations.(it may cut a cookie faster with a 8 pin .325)
A lot of 029 saws have been sold with 20" bars with both size chains, it's up to the user to decide which works best.

 

[Marshy]

1640 drive links per 100 feet. 3/8 is generic if you want to do the math do it right.

Yeah no doubt I overlooked that, oops. How many DL in a 100' of .325 pitch? What do you mean generic?

 

[nandoz]

This is false. At the same engine engine rpm the 3/8 chain will spin faster because the sprocket is larger.

I had it backwards. And that my friends is why you shouldn't drink and post. Or at least I shouldn't.

 

[Franny K]

Yeah no doubt I overlooked that, oops. How many DL in a 100' of .325 pitch? What do you mean generic?

1848 dl per 100' for 0.325 which is exact. 1/4 pitch chain comes out exact as well. Generic probably was not the best word, a close fraction that is easy to type or say might be more precise.

 

[AmateurSawer]

Thank you for all the replies.I think I have got a hold on it,now.The .325 he uses seems to cut better because of a narrower kerf the cutters take(like the small 3/8 chain on the "Wild Thing" saws.Dad had a Homelite Super EZ Auto back when I was younger.Ran 3/8ths pitch and with the lo profile chain,you could make some nice cuts building with rough lumber.
I currently run .325 chain on my 026 and 028. run 3/8th on the 362 mainly because that's what they came with.All run 20" bars ( the 026 and 028 for reach and conveinence) so I'm sure some would say I should swap out to 3/8 or put a .325 on the 362 to simplify chain.They have a point but all my bars are in good shape with a lot of wear left so unless I bite the bullet and give the 362's bars to a friend I wouldn't gain anything.

 

[lambs]

Did you run the 8 tooth sprocket when you ran the .325?

I think it was an 8. Not sure though.