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Simpleton7016

Pulley part number 174190

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Simpleton7016
is it advisable to do so? I am preparing this new deck with gator blades for the purpose of chewing up the onslaught of leaves that will be coming soon. What's to stop a guy from going to a 3 or 4 inch pulley? Can the bearings take it? Is there additional stress on the deck? Will it throw off the balance? Etc etc? I assume I would need to play with the belt size too then? Thnaks guys!

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BLT
Erik, blades should be in balance now and can be sharpened and re-balanced. I am taking a gut shot that the blades you have now measure about 17-1/2 inches diagonally across. You can safely spin the blades at 3900 RPM and stay within the 19000 feet per minute blade tip speed. The bearings will easily spin at 5000 rpm and so you have some margin there. I would guess stress on the deck wouldn't change unless you have a habit of blowing rocks. And yes getting a correct belt might required. I have a method to make that easier.

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Simpleton7016
On second thought, my purpose would be to reduce the size of the pulley to increase the speed of the blades. Then I could slow down the RPM's on the motor. However, if I decrease the RPM's on the motor, I will also decrease the amount of "suction" for the vac unit. Maybe I should just keep it all factory....:(

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BrianP
Interesting thread. I have a freshly restored 7016 also and the original 48" deck was so eaten up with rust I bought a newer used deck and transferred all the parts over. What a job that was. Anyway, I replaced the center arbor and one of the outboard ones. The new center arbor I bought from my Simplicity dealer came with a 4 inch pulley installed. Dealer instructed me to use my original pulley (6 inches in diamater, I measured it), in order for the deck to work properly. So, which pulley is the right one to use? I have noticed it doesn't seem to discharge the clippings very far. Another point, the belt (which I tripple checked, darned near drove the dealer nuts), almost touches where it crosses itself. Have I been using the wrong pulley all season? Did the dealer make a mistake? Did some (ahem) "previous owner" install an incorrect part? I kept the pulley that came with the new arbor, just in case.

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Simpleton7016
OK, there are certainly people smarter than me whom have figured this out. But let me share my math calculations and someone please point out my errors. Circumference = 2 x (3.14) x radius So the circumference of a 6 inch pulley is 18.84 inches. But the belt will only utilize 1/2 of the circumference. So the "used" portion of the pulley is only about 9.5 inches. So the circumference of a 3 inch pulley is 11 inches. Again, the belt will only utilize 1/2 of the circumference. So the "used" portion of the pulley is only about 6.5 inches. So the difference in belt length will be approximately 3 inches. The belt for the standard 48" deck with 6" drive pulley is part # 1722039 and it is 71.6 inches long. So if I decide to go with a 3 inch drive pulley on the same deck, I should subtract approximately 3 inches from that. Meaning I should buy a belt that is approximately 68.6 inches long. HOWEVER, there are a few other factors to consider. First, the belt does not sit on the outside of the drive pulley, so those measurements are off a little. I could probably get away with a 69" belt. Second, the idler pulley near the cone clutch should be able to take up some slack, so I think there is a little forgiveness built in. Anyone else ever do this? Will there be any problems running a 3" drive pulley? Will there be enough power to get that deck spinning? Will it tend to throw belts off easier or increase slippage? And Bob, can you use your calculations to let me know if the resulting RPM's on the bearings fall under the 5000 limit? Better yet, can you show us how you came up with those calculations? (Give a man a fish and he's fed for a day. Teach a man to fish and he is fed for a lifetime) :)

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BLT
Again here is how you determine safe blade speed. Manufacturers will take 90% of the final figure and round down another couple hundred RPM. That will keep the legal beagles off of their back. Measure corner to corner blade length in inches (that is longest dimension). Divide that by 12 equals feet. Mulitiply that figure by 3.1416, the diameter of a circle. This gives you the length in feet of one revolution. Divide that figure in 19000 and that equates to the maximum revs per minute allowed. A 20" blade is rougly 21" across. 21 divided byb 12 is 1.75 feet. 1.75 times 3.1416 equals 5.50 feet. 19000 divided by 5.5 equals 3455 blade RPM. The BGB turns engine speed and the pulley diameter for the mower belt is very close to 5". A three inch pulley will spin the blades 1.66 times faster times engine speed. A 5.5" pulley will spin the blades about 91% of engine speed and finally the 7" pulley will spin the blades at 71% of engine speed. The three inch pulley is prone to giving belt slip in heavy matrial as there is not much belt wrap. The 5.5" pulley appears to be the best choice for speed and belt wrap. I was wrong on the bearings. They can spin up to 8000 RPM and still give you some life before replacement. Everything I read says about the average life of the bearings in these arbors should be in the range of 500 hours or on car mileage terms 17,500 miles. Considering their crappy enviroment, that doesn't sound bad.

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Simpleton7016
Excellent explanation! Thanks! These pulleys aren't very hard to change once I have them de-rusted, primed and lubed. Maybe I will experiment a little and report back. I know I will have some additional questions shortly about spindle keyways, so more to come later. First I need to get some trolls to bed and take some pictures to better explain... But again, thanks. Sincerely!

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