Best rear sprocket size

Discussion in 'Hubs, Gearboxes, Sprockets and Chains' started by clay830, Jan 30, 2017.

  1. Tyler6357

    Tyler6357 Member

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    I agree with others, 36 tooth minimum with a stock China girl motor and stock pipe and even that will be kinda sluggish on the low end. Get an expansion pipe, high compression head, port the top end. Make sure you have brakes and a frame that can handle extra speed. Also, you might consider a sprocket adapter if you are using the stock rag joint for the rear sprocket, if you put too much torque on bicycle spokes they will bend or break.

    brnot
     
  2. sbest

    sbest New Member

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    The stock 2015 Grubee 66cc seemed to be happy up to 8000rpm, whereas the 2012 Grubee 48cc doesn't even live reving that high. I have a black no-name 66cc China Girl that seemed to only do about 6000-7000. All of this was easy to alter with some porting or a cylinder swap. Balance was another issue, with them getting better high speed balance as they got newer.

    So far I am running a 44t on my 66cc and very happy with the balance of speed with quick acceleration, hillclimbing and being able to crawl around on sandy and muddy trails.

    [​IMG]
     
  3. clay830

    clay830 Member

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    what size do you think I should get
     
  4. TheNecromancer13

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    I've said about 4 times now, as have others, a 36t at minimum.
     
  5. clay830

    clay830 Member

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    k thats what ill get
     
  6. clay830

    clay830 Member

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    another problem I'm having is with my chain. I tried shortening it 1 link because it was to long and the top half of the chain (going into the engine) was sagging and rubbing the bottom half. I shortened it and now the chain is to short and the master link won't reach both ends of the chain. What should I do? Add a half link/offset link?
     
    #46 clay830, Feb 15, 2017
    Last edited: Feb 15, 2017
  7. xXNightRiderXx

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    My bike is a 700x32c road bike with drop bars. I have a 66cc china girl and a 44t sprocket, and I get to 32mph risking ring flutter. Tire size definitely matters, so do other drive train upgrades. I'm getting a jackshaft to allow for speeds of possibly 55mph. My next build will be a 212 predator Cruiser with a backrest and extra long custom fenders attached to the frame at multiple points. It will also have a long shot muffler and the drive shaft will be lengthened to the native drive side. The chains will be 415h half links. There will also be two auxiliary fuel tanks. This bike should be able to drive at freeway speeds in relative comfort. Clay, if you have the tensioner installed, try lowering it, then try connecting the master link. If that doesn't work, try taking off the tensioner. If that still doesn't work, then you need a half link.
     
    #47 xXNightRiderXx, Feb 19, 2017
    Last edited: Feb 19, 2017
  8. clay830

    clay830 Member

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    Neither of those work. I have to get an offset link. I am debating on whether I should get the half link or just buy the sprocket and wait to install it and shorten the chain to match the sprocket. Anyway what size sprocket do you think I should get with a stock chinaman? 36 or 32?

    And if I replace the carb and get an NT speed carb then what size sprocket should I get? Or does it not make a difference?
     
  9. clay830

    clay830 Member

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    Do you guys think my bike would be able to pull a 32t or not? I really want the 32t but think I would be risking to much. The reason I want the tooth count to be as low as possible is so that I can be able to cruise at higher speeds than 25mph. With my stock china I can hit tops 30mph. If I put on a 32t, I could theoretically hit 40 mph at top rpm. Say my top rpm is 7000 and with a 32t at 4000-5000 rpm I could cruise at 33-35 or so but with a 36 I would be cruising at 29-30 or so with a top speed of 36mph. I want to be able to also ride at the highest speed possible on those back roads.
     
    #49 clay830, Feb 19, 2017
    Last edited: Feb 19, 2017
  10. xXNightRiderXx

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    Let's just say that my stock engine has a bit of trouble starting from a stop with the 44t. I doubt yours would be able to do much of anything fun with a 32t. I wouldn't go lower than 38t, but if you are looking for speed above everything else, then you do not go lower than a 36 for a 66cc china girl, as several others have said. If you have a welder or know someone who does, get a go kart jackshaft. That will completely eliminate the need for a rear sprocket, but you'd need to take the pedals off. That is not to say you absolutely need a pull starter, but you would have to put on the left side pedal every time you want to start it. The jackshaft will allow you to get to the highest speeds possible, while being able to climb mountains.
     
    #50 xXNightRiderXx, Feb 19, 2017
    Last edited: Feb 19, 2017
  11. TheNecromancer13

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    We have told you about 10 times already, no lower than a 36
     
  12. Chaz

    Chaz Member

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    Go for the 32 tooth and post your results. I think only then will you understand why everyone has advised you to not go below 36 tooth.
     
  13. clay830

    clay830 Member

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    how com none of you don't just buy a motorcycle
     
  14. Tyler6357

    Tyler6357 Member

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    If you really want to go 40mph, get a new pipe like one of these and forget about trying to put a 32 tooth sprocket on a stock china girl.

    http://www.ebay.com/itm/MOTORIZED-B...id=100005&rk=2&rkt=6&mehot=pp&sd=272478122764

    http://www.ebay.com/itm/131438635251?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT
     
  15. xXNightRiderXx

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    With a 44t sprocket, stock motor, I Just hit 38.54 mph at approximately 12,000 rpm. There was a bit of oil from when my plug loosened, and my motor got hot enough to start it smokin! I'm going to head to O'Reilly to check on my piston and cylinder wall once my engine cools. I probably should check on my rings too, huh? Clay, the reason we don't buy a motorcycle is because they are expensive, heavy, governed, complex, and fuel hungry. Motorized bikes are easily 1/15 the price, in maintenance, fuel, and up front cost. I can pay 20,000 for a motorcycle, or I can pay usually no more than 650 for a decked out motorized bike. Take your pick.
     
    #55 xXNightRiderXx, Feb 19, 2017
    Last edited: Feb 19, 2017
  16. Tyler6357

    Tyler6357 Member

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    If you want it to run cooler the best thing I can recommend is to get a high compression head with long fins, like the Fred Heads have, these 2 strokes rely on air flowing over the head to cool them and the fins also help dissipate the heat. Also, you might mix your oil/gas a little richer than normal if you plan on really winding up the RPMs on the open road. You can also try a cooler plug, if you are using a NGK B6HS, try a B7HS or B8HS. If you are still breaking your rings in, it's critical to not let it get too hot because of the extra friction during break in, stop and let it cool for a few mins on long trips.
     
  17. xXNightRiderXx

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    I already have an angle fire head that came stock with the engine. I do need a Fred head for the longer fins though. My head is kinda sparing on number and length of fins.
     
  18. Tyler6357

    Tyler6357 Member

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    Yeah but it's not just the long fins, the Fred Head is just thicker on the base part of it which really helps with the heat. I put a Fred Head on mine last year and I noticed a big difference for running temp from the slant head one I had, I would call it a dramatic difference. Fred Heads are kinda expensive but the imitation ones still show big improvement.
     
  19. xXNightRiderXx

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    Where would I find one of these imitations?
     
  20. Tyler6357

    Tyler6357 Member

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    Well, I scored one on ebay for a bike I am building from a guy for $40. Also, gasbike.net sometimes has them on sale for $45. Right now they have a duel spark one for $49.
    https://www.gasbike.net/collections...dual-spark-racing-cnc-cylinder-head-66cc-80cc
    The orginal FredHead sells for $60
    http://shop.crmachine.com/product.sc?productId=48&categoryId=15
    There are these colored ones, they look pretty good but I've never used one
    http://www.ebay.com/itm/Racing-CNC-...971233?hash=item41bcd552e1:g:~ooAAOSw2xRYlitN
    http://www.ebay.com/itm/Racing-CNC-...947239?hash=item41bcd4f527:g:WboAAOSw-0xYlivU
    http://www.ebay.com/itm/Racing-CNC-...976091?hash=item3f715ec5db:g:2TAAAOSwux5YUJNG
    http://www.ebay.com/itm/Racing-CNC-...087448?hash=item3f7479edd8:g:AjUAAOSw9GhYi99S

    Just keep checking ebay you will see them advertised often.
     

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