I need to re-bore a sprocket
Some background to my problem first:
I have a 75 tooth rear sprocket on my "Motovox MBX 10" (Chinese made, will explain later).
I replaced the stock 2 1/2 hp engine with a HF Predator 212, which I modified. http://www.oldminibikes.com/forum/project-logs/80616-predator-212-just-over-stock-build.html.
With a 12 tooth clutch, the gear ratio is 6.25:1. According to the math @ 48mph it's doing 7200rpm's. I don't
want to blow up my engine and I do have a lot of low end power, so I started thinking about gearing. Also,
I don't have much room between idle and engagement. So,
1) First I got a 14 tooth sprocket for my Max Torque clutch :thumbsup: & then the correct "drum" for the 13t+ sprocket
and I currently have on order the snap clips I'll need to put it together :cursing: feel me. I had a little more luck with the
Max Torque clutch "green" spring (locks at 2500rpm's) I found a video on you tube, just followed along & it's in!! Great!! :biggrin:
2) Next, went to the rear wheel sprocket and I took it off the wheel (btw the tires are 14" diameter).
HERE'S THE PROBLEM
The sprocket is a 75 tooth with an "unknown bore" and bolt pattern....:chinese: Thank You Very Much.
I'ts close to 1.466?" (or 1.5") & a 6 bolt pattern that's in a 2" circle. It's hard to buy a 60 tooth sprocket
when you can't match the bore, also I haven't seen a 6 bolt 2" circle pattern, so I did the best I could
and came up with a bore that is just a little smaller (1 3/8" bore). But, now my small engine machine shop says
they have no equipment to enlarge the bore and referred me to a CNC shop. They'll do it, but setting up the
CNC machine will cost about $125.00. :crying: This 60t sprocket was going to create the drag I'm looking for.
I really wanted this to work, because this engine has just too much low end power, almost no slip at all, can't rev.
A 14t clutch that locks @2500rpm's, that's 24.3 mph w/ a 60t rear sprocket & 14" tires, would "act" like a Harley.
Also, it would do 35mph @ 3600 rpm's so I could adjust the linkage "speed limiter screw" to stop @ say 4200rpm's
or 40.8mph. True it might cost a clutch or two, but it would save my engine, and it would be F U N !!!
HOW CAN I RE-BORE A REAR WHEEL SPROCKET??
Some background to my problem first:
I have a 75 tooth rear sprocket on my "Motovox MBX 10" (Chinese made, will explain later).
I replaced the stock 2 1/2 hp engine with a HF Predator 212, which I modified. http://www.oldminibikes.com/forum/project-logs/80616-predator-212-just-over-stock-build.html.
With a 12 tooth clutch, the gear ratio is 6.25:1. According to the math @ 48mph it's doing 7200rpm's. I don't
want to blow up my engine and I do have a lot of low end power, so I started thinking about gearing. Also,
I don't have much room between idle and engagement. So,
1) First I got a 14 tooth sprocket for my Max Torque clutch :thumbsup: & then the correct "drum" for the 13t+ sprocket
and I currently have on order the snap clips I'll need to put it together :cursing: feel me. I had a little more luck with the
Max Torque clutch "green" spring (locks at 2500rpm's) I found a video on you tube, just followed along & it's in!! Great!! :biggrin:
2) Next, went to the rear wheel sprocket and I took it off the wheel (btw the tires are 14" diameter).
HERE'S THE PROBLEM
The sprocket is a 75 tooth with an "unknown bore" and bolt pattern....:chinese: Thank You Very Much.
I'ts close to 1.466?" (or 1.5") & a 6 bolt pattern that's in a 2" circle. It's hard to buy a 60 tooth sprocket
when you can't match the bore, also I haven't seen a 6 bolt 2" circle pattern, so I did the best I could
and came up with a bore that is just a little smaller (1 3/8" bore). But, now my small engine machine shop says
they have no equipment to enlarge the bore and referred me to a CNC shop. They'll do it, but setting up the
CNC machine will cost about $125.00. :crying: This 60t sprocket was going to create the drag I'm looking for.
I really wanted this to work, because this engine has just too much low end power, almost no slip at all, can't rev.
A 14t clutch that locks @2500rpm's, that's 24.3 mph w/ a 60t rear sprocket & 14" tires, would "act" like a Harley.
Also, it would do 35mph @ 3600 rpm's so I could adjust the linkage "speed limiter screw" to stop @ say 4200rpm's
or 40.8mph. True it might cost a clutch or two, but it would save my engine, and it would be F U N !!!
HOW CAN I RE-BORE A REAR WHEEL SPROCKET??
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I found a machine shop today that said they don't have a problem