Jparkes43 329 #1 Posted April 24, 2016 (edited) Hello all. so my lawn ranger project is coming to the stage where i have all the pulleys off etc and i've wanted to increase the gear ratios for more speed. so my engine pulley was roughly 2" and my gearbox pulley was roughly 4" (roughly to make things easier and simpler to work out) because i want to save money and time if i swap over the two pulleys (same shaft size) that means i will go from a 2:1 gear ratio to a 1:2, am i correct?? so i'm running a 3 speed uni drive gearbox. Question b. With my hypothetical setup what speeds should i be expecting? in the three gears. Extra information. i'm running a tuned honda gx200 capable of 6000 rpm roughly. thanks and sorry its probably a really simple question but this topic isn't my strong point james Edited April 24, 2016 by Jparkes43 Share this post Link to post Share on other sites
Jparkes43 329 #2 Posted April 24, 2016 Heres some pictures incase it helps. thanks James Share this post Link to post Share on other sites
953 nut 51,881 #3 Posted April 24, 2016 If you were to go with two 4" pulleys it would double your speed; if you did what you are proposing it would be advisable to have an ambulance standing by the first time you used it! I doubt that a small 2" pulley would be workable as a driven pulley, probably too much slippage on take off........ One thing you must consider is that the brakes were not made for high speed operation. If you do give it a go, please take a video of it, we would love to watch! 3 Share this post Link to post Share on other sites
Racinbob 10,339 #4 Posted April 24, 2016 I did swap the motor and the transmission input pulley on a 551 almost 40 years ago. Your comment on the ambulance is spot on. We lived on a side road so I tried in on the blacktop. I quickly learned the error in my judgement. No, I didn't crash it but believe me, the steering on a 551 wasn't designed for those speeds. I drove it back to the house in 1st. 3 Share this post Link to post Share on other sites
wallfish 15,940 #5 Posted April 24, 2016 (edited) There are plenty of pulley/sheave calculators on the net which will save you some time and money vs the trial and error process. Here is one you can use. http://www.blocklayer.com/pulley-belteng.aspx Built one a while back that did around 40 mph and if I remember correctly, it had a 1 3/4 - 2" pulley on the trans but it had an 8 speed trans with 1 1/8 axles too. I used an idler pulley to keep the belt routed for the most belt contact around the small pulley. Also used a 1/2" Kevlar belt so it could make that tighter radius better than a 5/8" belt could. The 12 hp Kohler was set at 3600 RPM so you are going to go quicker just with the RPM output of that engine but mine also had a jack shaft with more pulleys to increase the drive pulley speed. I'd guess with your pulleys and that RPM it would be close to what that tractor was spinning. The gear oil in the trans was replaced with motor oil for reduced friction and at that speed it would be splattered around instead of needing to cling to the gears to distribute lube. MAKE SURE the brake band and drum are clean, clean, clean and completely free of grease and oil by soaking them in solvent. I just used gasoline. When applying the brakes hard on that tractor, the rear wheels would actually spin in different directions just like if it was jacked up because the brake drum would lock. Certainly not the best braking system for those speeds but it would stop pretty quick and enough to control it. Definitely do some research for setting up the front end. A little caster and toe in make a lot of difference. You need to be in control of it. Don't use the old WH tie rods either, buy new adjustable and better quality because you don't want one of those to fail at higher speeds! Edited April 24, 2016 by wallfish 2 Share this post Link to post Share on other sites
Jparkes43 329 #6 Posted April 25, 2016 Ok thanks everyone for all your inputs! you thought about the things that i wouldn't have so i really appreciate it. Will have to give it some thought on my options. I will get back to you on this. James Share this post Link to post Share on other sites
pfrederi 17,164 #7 Posted April 25, 2016 I played around a bit with getting a bit more speed on My L107. I finally settled on a 3" pulley on the tranny. By experimentation found a belt and the speed in 3rd was good. Problem...couldn't shift it. Went back to original. Solution would be to modify the belt guard to keep it close to the new smaller rear pulley...haven't gotten around to it yet. Share this post Link to post Share on other sites
Jparkes43 329 #8 Posted April 25, 2016 Ah ok sounds good! i might do that then. what sized front pulley did you have?? What do you mean?? not quite seeing what the problem was. James Share this post Link to post Share on other sites
pfrederi 17,164 #9 Posted April 25, 2016 the belt has to press against the lower edge of the belt guard when the clutch is disengaged. If it has to drop too far to the belt guard it won't fully disengage from the engine pulley and will keep moving, spinning the gears making shifting impossible. The picture tries to show how close the lower lip of the guard has to be to the pulley to force the slack up to the engine when you disengage clutch. Engine pulley is 2-1/2. 2 Share this post Link to post Share on other sites
Jparkes43 329 #10 Posted April 25, 2016 ok thanks that explains it thanks. And oh ok so close to what i have. that might be worth a go then getting some new pulleys. maybe keep the gearbox one the same for ease of use and then increasing the size of the one on the engine. Who knows ill give it some thought and will see what i come up with Thanks James Share this post Link to post Share on other sites
