Left side drive Seat Post Jackshaft Bracket for 4" Fat tire bike.

4" fat tire JACKSHAFT FOR LEFT SIDE Single Speed Drive. 

This Seat Post Jackshaft Bracket is for left side drive.    It is for a mounting a 2 stroke China Doll engine inline Mid-frame on a Micargi Slugo 4" single speed Fat Tire 26" Cruiser Bike.    THEREFORE, THE ENGINE IS NOT Offset! 

Don't have a Micargi Slugo Bike?  No problem, we can sell you one dropped shipped from MiCargi Calif. warehouse.  

Our SeatPost Jackshaft fits a 28mm dia. steel seat post that is 3" away from the 4" rear tire.       

We 100% guarantee to fit the 26" Micargi Slugo 4" tire bike frame!

  • FYI:  We will only make 35 of these CNC SEATPOST JACKSHAFT KITS to test the market.  

Made in USA   Means highest quality workmanship!  Maybe we will make these Seatpost Jackshafts in the future in China but not certain if and when.

First time offered:     

  • USA Machine shop made.   Repeat  > NOT MADE IN CHINA.                      Made in Oklahoma by me and the 7D CNC machine shop in Boswell OK!  

  • Especially designed for Micargi Slugo 26" 4" tire bikes that have 3" clearance between seat post and tire.  However, may fit other brand bikes but must have the said 3" tire clearance and 28 to 28.5mm dia. steel seatpost. 

  • To avoid a return for non-fit measure your bike before buying to avoid a restocking charge. 

  • NOTE:  4" tire Slugo Bikes can be ordered from us and yes, they have the required 3" clearance and 28mm dia. seat post. 

  • By using our CNC solid billet jackshaft bracket the 2-stroke engine remains in the middle frame position same as would be in a standard 2"-inch tire bike thus giving best balance and professional look.   Problem solved!

  • Up until now the only way to have an engine on a 4" tire bike was to offset it to the left.  Problem Solved!

  • The GruBee Seatpost Jackshaft Bracket allows the engine drive chain to drive an inboard 9T sprocket and the outboard 10T sprocket allows chain clearance to go on past the 4" tire and drive the rear wheel on the left side.   Problem solved

  • The problem of how to tighten the engine chain to the inboard sprocket is solved by our Non-concentric Cam Lock Hub, same idea as used in our 4G 4 cycle transmission.  Problem solved!

  • Heads up:  In the future we will be supplying CNC solid spacer blocks and longer M8 Studs that pushes the engine forward to the bike's downtube but temporarily we will include 2 additional engine mounting blocks and (2) 8Mx110 studs.

  • BOM:   BUILD OF MATERIALS

  • 1.  2 pcs. Seat post mounting bracket and hardware. 

  • 2.  Cam lock cylinder and hardware   

  • 3.  Stainless Steel Shaft and (2) 5x5x20 keys. 

  • 4.  (2) 10T & 9T sprockets with set screws.

  • 5.  (3) 15mm ID Spacer washers.   

  • 6.  Dual spacer blocks and (2) M8-1.25x100 threaded studs. 

  • Customer must make their own sheet metal chain guard and obtain the required 415 drive chain.   ( Chain and chain guard are Not Included. )   Rear wheel must use a disc brake hole pattern sprocket and frame spaced out for clearance. 


  • Due to high cost $125 / hour CNC SHOP USA labor rate we will only make 35 of these Beautiful CNC SEATPOST JACKSHAFT KITS to test the market before taking the project to Riceland.   

  • By Mid-July 2024 we hope to have received our multi-speed right hand chain drive Kits.  yes, the kit that chain drives down to the right-side bottom hole with an inboard freewheel sprocket driving a 1/2x3/32" chain to a Multi Speed rear axle.     A rope pull or drill start engine is a requirement.