Largest rear sprocket available for MiniBaja MB-165 ?

#1
I am 99 percent sure my cycle uses 420 size rear chain and I see this sprocket from OMB
https://www.ombwarehouse.com/steel-sprocket-60-tooth-41-chain.html
and I wonder if it is the largest. The same company also sells a 72 tooth sprocket "blank" but I think blank means no holes. That wont work unless I can place my old sprocket over the new one and drill new holes.... I'd rather buy something ready to bolt on. Any suggestions for a larger sprocket source ?
 
#2
Blank sprocket means no holes and yours uses 420 chain.

It might be easier to mess with the gearing on the jackshaft instead of the rear sprocket.
 
#6
Yes, thank you. That is great news but we know it cannot be cheap. Before I spend lots ( more ) of money I would like to survey the market to find what is standardly available instead of custom.
 
#7
I found a split sprocket 66 tooth using 420 chain that will fit a sprocket adapter that bolts right up to MiniBaja or Coleman large bikes.
I do believe I have found the largest rear sprocket standardly available. I would conceivably be easier and cheaper to change the sprocket on the jackshaft to achieve the same change in gearing ratios but I have never seen any mention of modifying the original centrifugal clutch and jackshaft trannys.
 
#10
I see at that link the many size options for MiniBaja and Coleman including the 72 tooth sprocket and that they have
4 holes 3/8"
3.150" Bolt Circle
1.580" Center hole
So are these the defining requirements for rear sprockets for MB165 and Coleman type mini bikes ?

I am doing the slowest possible rock crawling and riding up dry creek beds and weaving through trees in dense forest etc.

It further states that the USA standard 6" wheel has a 2 7/8" bolt pattern which is not compatible
 
#11
Correction.... I will find out soon enough first hand but there is some disagreement whether the bolts that hold the sprocket to the wheel are fully 3/8s of an inch or actually 5/16 inch. I assume both will work but if the bolt and hole are actually very snug, the overall strength would be increased by a hundred percent or more. Again specifically talking about the Baja MB-165 in case there was ever an evolution of design in the sprocket connections. Further, I want the bolt hole and bolt very snug because I am considering the exploration of moving the sprocket away from the wheel a little in order to provide greater clearance between the chain and the tire. I may experiment initially by using quantities of washers as spacers and if nuts are screwed to the end of the mounting bolts I will make sure they both are grade 8 so that I can put the very maximum torque and squeeze on the stack of washers.
 
#12
I used Gopower's 60 tooth on my MB165. Perfect fit, no problems. They also have an aluminum 72 tooth option.
https://www.gopowersports.com/4-hole-mini-bike-sprocket/
Well it turns out the GoPower Sports has the largest available sprocket for Mini Baja MB-165 amd MB-200. It is 72 teeth BUT they misrepresent the sprocket on their website by saying it is Aluminum. I ordered one and it is NOT aluminum. It is steel. I expect one third decrease in speed and one third increase in torque. This I assume when used with the centrifugal clutch will act like a granny gear in trucks and jeeps etc.
 
#13
Well it turns out the GoPower Sports has the largest available sprocket for Mini Baja MB-165 amd MB-200. It is 72 teeth BUT they misrepresent the sprocket on their website by saying it is Aluminum. I ordered one and it is NOT aluminum. It is steel. I expect one third decrease in speed and one third increase in torque. This I assume when used with the centrifugal clutch will act like a granny gear in trucks and jeeps etc.
You should consider a torque converter, too. Paired with a 72 tooth, you’ll be fine with hills, and you can actually get enough speed if you gear it correctly. Best of both worlds.
 
#14
You should consider a torque converter, too.
They are pretty awesome and not too expensive if you go with one of the Chinese knock-off ones.

Running a Chinese backing plate with Tav30 everything else since I had to cut it up to make it work with my setup. Love the thing.

I want different minis so I have this one with a TAV, one that I'm currently working on that will be 15hp+ with a clutch setup and another with a pit bike engine (110cc, 4 spd) in it. I'm on the fence about putting a 140cc engine in the one so it has a bit more power.

 
#15
I would consider a Torque Converter and may get around to it but the known good ones cost $200 and no one seems to have sorted out
the crap and junk from the asian suppliers. While the technical literature says the TQs have a variable gear ration of 3X, no one I read about is experiencing any kind of change of performance that reflects that big of a range. That leaves me very curious. I am not sure I will get an increase in performance of any kind that is worth $200 plus a good bit of labor .......
 
#16
PS.... It is hard for me to justify a TQ for $200 verses a brand new engine that is only $99 at Harbor Freight. It would be nice to list the different Chinese suppliers along with a poll of users so we could weed out the crap suppliers vs others with decent products.
 

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