Why does my Stihl 029 Super list both a 7 tooth and 8 tooth sprocket for .325 pitch? Do they both fit the same chains? What's the advantage of each?
why both 7 tooth and 8 tooth sprockets?
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Chain drive link count yes. 7 tooth more torque-standard setup. 8 tooth-more chain speed but less torque and therefore more prone to bogging in hardwoods if you lean on it a little. If you've go a rim sprocket setup on the saw it would be cheap to try out both and decide for yourself.
It is sort of like the rear-end ratio in a car - the number of teeth on the sprocket will influence the speed of the chain at a given engine speed, as it will change the number of drive links going past a given point per engine revolution... However unlike the acceleration vs. top speed equation you get with a car, in a chainsaw it's mostly a question of balancing the load on the chain with the engine output at full throttle.
Ideally you'd like to keep the full throttle engine speed within a fairly narrow range, where it produces the peak torque... You would use the smaller sprocket with a heavier load as that takes less power to turn the sprocket - examples might be a longer bar, or a more aggressive chain. The chain will move slower, but with more power
OTOH, if you are lightly loading the saw, either with a shorter bar, or a less aggressive chain, then the larger sprocket would give a higher chain speed, but be more prone to bogging if you lean on the saw to hard.
Gooserider
Ideally you'd like to keep the full throttle engine speed within a fairly narrow range, where it produces the peak torque... You would use the smaller sprocket with a heavier load as that takes less power to turn the sprocket - examples might be a longer bar, or a more aggressive chain. The chain will move slower, but with more power
OTOH, if you are lightly loading the saw, either with a shorter bar, or a less aggressive chain, then the larger sprocket would give a higher chain speed, but be more prone to bogging if you lean on the saw to hard.
Gooserider
Thanks, makes sense. I've been running an 8 tooth and it does tend to bog in hardwoods a bit. I'll try the 7 tooth and see how that does.
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