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Post by sweepleader on Mar 7, 2018 7:35:04 GMT -5
9 pin would be over 28% increase in speed and reduction in torque, is that actually workable? I put an 8 tooth on my XL-500 and it loves it but that is only 14%. Just asking, I have never run a 750 so I really have no idea. This is something I would like to see a deeper, more detailed conversation about. Never messed with the output end of a saw before, besides just a longer bar. From whence do these calculations derive? These calculations are pretty straight forward, unless I have missed something important. (I hope someone would point out errors.) All I did was devide 8 pins by the standard 7 to get 1.142... and called it 14% overdrive. A standard gearing calculation. Similarly with 9 divided by 7 to get 1.285..., called that 28% overdrive. That would indicate that at the same engine speed, changing sprockets would result in that much faster chain. Torque at the sprocket or tension in the chain would be reduced a similar amount. It is pretty tough to be exact as there are other factors involved such as chain pretension, hard nose or roller, oil, etc. A longer bar as most could guess results in more friction between the chain and the bar in addition to more cutters in a bigger log. Chain speed increases also result in friction changes but it is hard to guess if the speed might be high enough to "hydraulicly float" the chain on an oil film or just make more drag. Friction and wear tends to increase with the square of the speed, doubling the speed increases the ill effects by a factor of 4. Speed is a double bitted ax in this case. If you have the power and don't mind the wear, speed is really fun. I made the 7 to 8 tooth rim sprocket change on my XL-500 with a new 16" bar. I had to take the rear upper corner off the bar so the 7 tooth chain fit the 8 tooth rim. That also brought the rear of the bar very close to the rim to help prevent derailing the chain at the higher speed. I am not a chainsaw racer, your mileage may very. |
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Post by sawnami on Mar 7, 2018 7:51:01 GMT -5
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Post by sweepleader on Mar 7, 2018 7:55:18 GMT -5
Good stuff ^^^.
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Post by undee70ss on Mar 7, 2018 12:59:57 GMT -5
I have no real personal experience with this.....
Saw type also makes a difference. All of Homelites big reed valve saws (S1050, 2100 ect...) all came with a 8 tooth standard, but they don't turn the RPM's that a 750 does.
750's came with a 7 tooth standard, and a 8 tooth optional. You probably wouldn't want to use a 8 tooth on a long bar in big wood. I thinking about using a 8 tooth with a 20-24 bar on my 750. Iv'e only used a 7 tooth so far.
Anything bigger than a 8 tooth might require a custom bar, to prevent derailing issues.
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Post by stillsawing on Mar 7, 2018 20:07:12 GMT -5
3/8 pitch has normally been used with 7 tooth clutch drive as mentioned in the previous information. .404 requires 8 tooth to get enough circumference for the larger chain drive tangs. What was not mentioned was the type of chain and cutter is to be used. Skip, semi skip, full comp, chipper, semi chisel, full chisel, these preferences are to be considered. Also it depends on the types of wood is being cut. Most bars 28" and longer with either pitch, some form of skip chain is considered for hardwoods. And then plunge cuts are avoided, kickback is more prevalent. All of the options involved in the end configuration is swayed by the geographic area, eastern vs western.
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Post by Clasec on Mar 8, 2018 23:56:10 GMT -5
I've ran a 8 tooth rim sprocket and a 20 inch bar full chisel on one my SXL925's for several years. You can tell the difference in cutting speed right away over stock. Never threw the chain off or any problems. I think a 750 with an 8 tooth would be a beast with a 24 inch bar.
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