.325 or 3/8 on Stihl 036?

[mountainlake]

325 7 pin cuts faster than a 3/8 7pin on smaller saws cuz it puts more torque to the chain, same reason why the Dolmar 7900 cuts faster with the 7 pin 3/8 vs 3/8 8 pin . Kerf size is just about the same on my 325 and 3/8, you can make a cut halfway with the 325 and the 3/8 has no problem fitting in it. I think you can get a narrow kerf 325, mine isn't. Why are we talking about a 325 8 pin, may as well run a 3/8 7 pin. Running to much chain speed is like gearing your 4 cylinder car for 200 mph, it won't pull it, a hopped up V8 will. Steve

 

[SawTroll]

Hi
what does a chainsaw do?
The fast running 2-Stroke engine pulls a well sharpend chain trough woodenmaterial. And makes chips.

Now it is the Question: what is faster in the same Diameter with the same saw: .325"by 8pin or 3/8"by 7pin on the SM7 shaft?
It gives the number: chipvolume per time

By the way: i burn cookies in the grill.

Cheers Vincent

Sort of, but the initial higher chain speed with larger sprockets soon turn into a loss (because of less torque to keep the rpms up), if the saw doesn't have enough power to compensate for the torque loss at the sprocket.

You can compensate (to a degree) by keeping the rakers higher - but that will result in less chipvolume per time, as well.

A narrower kerf chain may also help, but then other issues tend to appear - like chain design.

 

[timberwolf]

Here is a chart with some chain speed calculations.

3/8 with 7 pin is a slightly higher chain speed than .325 with 8 pin.

There are many .325 chains that have a much smaller tooth than full 3/8 chain, I have found these to be significantly slower than 3/8 chain all else being equal. Chain like .325 Stihl RS has a larger cutter and performed better than the smaller cutter .325.

I think about 50 cc with a 16 inch bar is about the break point where a switch from .325 to 3/8 makes a difference. But that depends a lot on sharpening, as well as the size and type of wood. But saws less than 50cc likely do better with the lighter .325, bigger saws in bigger wood need the chip clearing of 3/8 and should have the power to pull it.

In green are chain speeds less than 75 mph, this seems about tops for any factory saw/chain set up WOT. In yellow is up to 100 mph, this is exceeding factory chain speed your on your own for your safety. In red is over 100 MPH, I know I have derailed chains run this fast, very likely unsafe to run a chain this fast, though I know some do run race chains up there.

 

[RiverRat2]

Good Post TW!!!!!!

 

[mountainlake]

Here is a chart with some chain speed calculations.

3/8 with 7 pin is a slightly higher chain speed than .325 with 8 pin.

There are many .325 chains that have a much smaller tooth than full 3/8 chain, I have found these to be significantly slower than 3/8 chain all else being equal. Chain like .325 Stihl RS has a larger cutter and performed better than the smaller cutter .325.

I think about 50 cc with a 16 inch bar is about the break point where a switch from .325 to 3/8 makes a difference. But that depends a lot on sharpening, as well as the size and type of wood. But saws less than 50cc likely do better with the lighter .325, bigger saws in bigger wood need the chip clearing of 3/8 and should have the power to pull it

It doesn't have anything to do with chip clearing unless your running a low profile junk chain. Please explain why the Dolmar 7900 cut faster with a 7 pin3/8 compared to a 8 pin 3/8, most likely the same chain, It for sure didn't have anything to do with chip clearing, it had everything to do with more torque being applied to the chain. It's not rocket science. Steve

 

[timberwolf]

I would have to say it may have to do with sharpening.

I know with any 80 cc saw even stock I am familliar with the saw will cut faster with an 8 pin 3/8 gear than 7 this given were talking less than 12 inch wood or so and a chain that is filed properly with rakers at a reasonable height. If the rakers are taken down on a 7 pin to make it load the engine and cut then it may be too much to run with an 8. but the chain with 8 pin and the right raker clearance will outcut the chain with 7 pin and filed down rakers.

With a ported 80cc saw and race chain it'l pull 9 tooth 3/8 with a light touch and can cut faster. A good ported 90cc saw can even pull 10 to give the fastest times.

I have even tried .325 chain run with a 10 tooth gear on 90 cc saw, at this point chip clearance was a problem even cutting 10 inch softwood. lots of recut chips in the chip pile, and hesitations in the cut where the chain would essentially float on re cut chips and stop cutting.

Please explain why the Dolmar 7900 cut faster with a 7 pin3/8 compared to a 8 pin 3/8, most likely the same chain, It for sure didn't have anything to do with chip clearing, it had everything to do with more torque being applied to the chain. It's not rocket science.

Guess all the racers are going to be selling of the big sprockets to buy up 7 pin gears so they can get more torque on the chain and win races. LOL

 

[timberwolf]

Maybe another way of looking at it is like an example of driving nails.

If we were to have a race driving twenty 3 inch nails one guy was given a very small tack hammer, one guy given a faming hammer and another guy a 25lb sledge. I would put the money on the guy with the faming hammer.

Sure the guy with the tack hammer can move fast and hit the nail like a wood pecker on a tin roof, but his hammer lacks the energy to move the nail much on each swing. The guy with a slege can only swing it once every 10 seconds, but will bury a nail in a single swing and has a sweat on by the 5th nail. The framing hammer is matched to the job.

Same goes with chain, gear up too much and the losses in moving the chain at high speed become inefficiencies and waste power resulting in a slower cut. Gear too low and take the rakes down and the wood cutting by the teeth becomes inefficient as it is hard to split off thick shavings from a block as anyone who has carved or used a wood plane will know. Also the forces from the chain to the bar go way up due to the increased pressure placed on each cutter, compounding that the chain is forced out to the side more resulting in a wider kerf and a rough cut. This becomes inefficiency and results too in a slower cut.

 

[SawTroll]

...3/8 with 7 pin is a slightly higher chain speed than .325 with 8 pin. ....

I believe it is the other way around, but no big deal really.....

 

[tomtrees58]

3/8 on 038 325 four 026 028 tom trees

 

[timberwolf]

I believe it is the other way around, but no big deal really.....

.325 x 2 x 8 = 5.20 inches of chain each rotation
.375 x 2 x 7 = 5.25 inches of chain each rotation

The diamiter of the sprockets them selves is only part of the riddle. got to also look at the height of the drive links from the bar rail to centerline of the rivets, 3/8 chain is bigger there too and effectly makes the sprocket diamiter larger.

But in any case it is the number of gear teeth and the pitch that maters and when the math is done .375 (3/8) 7 pin will produce a slightly higher chain speed than .325 8 given the same RPM.

Your right though it is no big deal though, very close, just you said something in a way that was not entirely correct in the context we were talking. Granted now if we throw chain weight difference into the pot and differences in bar friction 3/8 vs .325 a saw may turn higher RPM WOT with .325 chain resulting in a higher chain speed WOT unloaded.

 

[SawTroll]

.325 x 2 x 8 = 5.20 inches of chain each rotation
.375 x 2 x 7 = 5.25 inches of chain each rotation

The diamiter of the sprockets them selves is only part of the riddle. got to also look at the height of the drive links from the bar rail to centerline of the rivets, 3/8 chain is bigger there too and effectly makes the sprocket diamiter larger.

But in any case it is the number of gear teeth and the pitch that maters and when the math is done .375 (3/8) 7 pin will produce a slightly higher chain speed than .325 8 given the same RPM.

Your right though it is no big deal though, very close, just you said something in a way that was not entirely correct in the context we were talking. Granted now if we throw chain weight difference into the pot and differences in bar friction a saw may turn higher RPM WOT with .325 chain resulting in a higher chain speed.

3/8" chain actually have a .367 pitch - .375 is just a translation of 3/8.

.367 x 14 = 5.138.

Btw, .325x9 and 3/8x8 are even closer.

 

[timberwolf]

Thought it was just 3/8 low pro that was under at roughly .370?

 

[SawTroll]

Thought it was just 3/8 low pro that was under at roughly .370?

Standard and lo-pro both are .367, but the chassis and drivers are different,. so they need different sprockets - lo-pro rims actually have a larger diameter.

 

[timberwolf]

Hats off to ya sawtroll, I learned something today.

Will revise the chainspeed chart. lol that would put it 2% off

 

[nikocker]

Yikes!

There isn't going to be a test on this is there????
Al

 

[ray benson]

When you order a 100' reel of 3/8 or 3/8 low pro - you get 1640 drive links.

 

[SawTroll]

When you order a 100' reel of 3/8 or 3/8 low pro - you get 1640 drive links.

Yes, that was the final proof to me - some time ago!

 

[mountainlake]

I would have to say it may have to do with sharpening.

I know with any 80 cc saw even stock I am familliar with the saw will cut faster with an 8 pin 3/8 gear than 7 this given were talking less than 12 inch wood or so and a chain that is filed properly with rakers at a reasonable height. If the rakers are taken down on a 7 pin to make it load the engine and cut then it may be too much to run with an 8. but the chain with 8 pin and the right raker clearance will outcut the chain with 7 pin and filed down rakers.

With a ported 80cc saw and race chain it'l pull 9 tooth 3/8 with a light touch and can cut faster. A good ported 90cc saw can even pull 10 to give the fastest times.

I have even tried .325 chain run with a 10 tooth gear on 90 cc saw, at this point chip clearance was a problem even cutting 10 inch softwood. lots of recut chips in the chip pile, and hesitations in the cut where the chain would essentially float on re cut chips and stop cutting.



Guess all the racers are going to be selling of the big sprockets to buy up 7 pin gears so they can get more torque on the chain and win races. LOL

So now were talking about hopped up 80cc saw cutting 12" wood ( most likely soft wood) I'm sure a 8 or 9 tooth would cut faster than a 7. No stock 50cc saw is going to cut faster in bigger wood with a 3/8 chain. Steve

 

[timberwolf]

LOL, I have a 260 work saw that cuts much faster with 3/8 7 , it even will run 3/8 8 and cut as fast or faster, but takes a light touch. I have a bone stock 026 will give you some video.

And it does not have to be a hopped up 80 cc saw, even something in the low 70s can take advantage of 8 with a shorter bar and chain (16 inch).

A lot has to do with chain sharpening.

 

[ZeroJunk]

I have an 064 that works well with a 3/8 8 and a 20 inch bar. But ,I normally use a 28 inch bar on that saw and with the 3/8 8 you really have to finesse it too much and it's prone to derail. Nine times out of ten I'm cutting red oak.


Sounds like my best bet on the 036 is 3/8 7 and a 20 inch bar.

This has been an education.