Rim Sprockets?

[Big Neb]

I just noticed that on my two 7900s, one has a 7 tooth and the other has an 8 tooth.

Is there much performance difference or is it mainly to accommodate chain lengths?

Are there any advantages with spur sprockets?

 

[cuttinscott]

I just noticed that on my two 7900s, one has a 7 tooth and the other has an 8 tooth.

Is there much performance difference or is it mainly to accommodate chain lengths?

Are there any advantages with spur sprockets?

7 tooth is stock set up from factory, although we have set up many at point of sale to 8 tooth 24" and 20" combos this does make torque go away a bit but it still handles it with ease.

Spur sprockets ADVANTAGE?? NO Possible advantage to a spur sprocket.. other that initial PRICE

Scott

 

[chainsawjunky]

Anyone correct me if I'm wrong but the 7 tooth creates more torque. And the 8 tooth spins it faster. Evan

 

[TDunk]

Anyone correct me if I'm wrong but the 7 tooth creates more torque. And the 8 tooth spins it faster. Evan

+1, i think

 

[cuttinscott]

Anyone correct me if I'm wrong but the 7 tooth creates more torque. And the 8 tooth spins it faster. Evan

Thats what I implied it might not have sounded that way sorry

Scott

 

[PA Plumber]

I went from a 7 to an 8 recently on my 026. Torque loss is very minimal, but definitely getting more fuel mileage from a tank of gas. I used to be able to get about 3 1/2 Hemlocks limbed on a tank, now can get nearly done with the fourth tree. I try to keep a sharp chain on my saws to minimize effort in the cut.

 

[rreidnauer]

Anyone correct me if I'm wrong but the 7 tooth creates more torque. And the 8 tooth spins it faster. Evan

I guess one could be real nit-picky and say both sprockets spin at the same exact speed. It's chain speed which will differ. 7 drive links per crank revolution verses 8. That's a 15% increase in chain speed. (and naturally, a 15% torque loss, but chain speed should make up for most of it)

 

[TDunk]

I guess one could be real nit-picky and say both sprockets spin at the same exact speed. It's chain speed which will differ. 7 drive links per crank revolution verses 8. That's a 15% increase in chain speed. (and naturally, a 15% torque loss, but chain speed should make up for most of it)

Your one smart feller.

 

[begleytree]

Your one smart feller.

yes he is.
but its also something a lot of us already knew. we just hadn't gotten around to telling you yet! lol

and I think its more like 13% or 14% due to cutting drag, but out of the wood yup, simple math shows 15%. a high gear slows the engine easier than a low gear when under load. would be very interesting to see a max rpm out of wood and engine rpm with a 7 and 8 in the same wood. have to use the same bar/chain and one hand it and let it pull in itself to remove operator inconsistancies in pushing. and time the cuts too. if I had a tach I think itd be a neat test to do. ie 8 pin cut .3 sec faster and ran 700rpm slower at WOT in the cut verses a 7 pin. or something like that.
-Ralph

 

[B_Turner]

I used to switch between 7 and 8 with my bigger saws (066 and 395) depending on bar length (28 is short to me and 36 or bigger is long) but I found it really wasn't worth the trouble. Unless you are running a bar that is pretty short for the saw, the 7 pin generally will cut as much wood by the end of the day with a bit less trouble.

JMO.

 

[NovaMan]

I went from a 7 to an 8 recently on my 026. Torque loss is very minimal, but definitely getting more fuel mileage from a tank of gas. I used to be able to get about 3 1/2 Hemlocks limbed on a tank, now can get nearly done with the fourth tree. I try to keep a sharp chain on my saws to minimize effort in the cut.

What size bar?

 

[SawTroll]

I guess one could be real nit-picky and say both sprockets spin at the same exact speed. It's chain speed which will differ. 7 drive links per crank revolution verses 8. That's a 15% increase in chain speed. (and naturally, a 15% torque loss, but chain speed should make up for most of it)

It all depends on exactly what you are doing, the saw in question, and the way you use it.

Sprocket rims are cheap, so just experiment, and see what you like the best...

 

[SawTroll]

What size bar?

Probably pretty short, and limbing only.......

My favourite limbing setup is the MS361 with 15" bar, and 3/8"x8 + 36RSC.

 

[TDunk]

yes he is.
but its also something a lot of us already knew. we just hadn't gotten around to telling you yet! lol

I already knew about different sprockets sizes changing gear ratios from racing motocross, what i was suprised about was that Rreidnauer knew the percentage of chain speed gain vs. the torque loss right off the top of his head.
And your a smart feller to Begleytree

 

[rreidnauer]

. . . . what i was suprised about was that Rreidnauer knew the percentage of chain speed gain vs. the torque loss right off the top of his head.

Well, I'm not that clever. I did punch a few buttons on a calculator.

 

[A100HVA]

opcorn: has anyone ever tried a 9t .325 rim on a 357xp with 21LP chain & wide tail small mount bar (ko95)oregon

 

[PA Plumber]

What size bar?

18" bar, .325 chain, 74 drive links.

 

[SawTroll]

Well, I'm not that clever. I did punch a few buttons on a calculator.

Hmmmm - I tought it was 14%, but I didn't do the maths myself........

 

[rreidnauer]

Hmmmm - I tought it was 14%, but I didn't do the maths myself........

Well, actually yes, it's a 14.3% (14.285715% to be exact) increase in speed for the same given RPM.

Now to really mess with your minds, going from 8T to a 7T is only a 12.5% decrease in speed for the same given RPM.

Ponder that one for a while. :biggrinbounce2: :monkey: :bang: opcorn:

 

[Tzed250]

Or we can think of it as gear ratio:

7T rim with a 72 DL chain= 10.29 gear ratio

8T rim with a 72 DL chain= 9.00 gear ratio