Race bikes that don’t have a starter motor or a kick starter can be a pain. Small 2 strokes you can start on a stand, and run starting is always a possibility… but here’s how to make some roller starters using a 9″ angle grinder and some DIY skills.
We have a plan to construct either drawings you can take to a CNC shop to get everything cut out & bolt or weld it up yourself, or supply it as a kit of parts and you source your own stuff as required. Let us know if you’re keen!
- Angle grinder choice
- Axles, bearings and drive options
- Roller options
- Switching & wiring stuff
- The build!
Angle grinder choice
You want something beefy for this task: it needs to spin fast enough that the gear ratio between the rear wheel and the rollers you select is going to spin the motor fast enough. This takes some maths that we’ll get you through, but, for the moment 5-6000 rpm is sufficient. Power wise you want something grunty – look for a 2+ kW 9″ grinder to make this work.
For this one, I’ve selected a cheap Ozito from Bunnings. I paid $109 on special in 2015, the retail price was about $129 so something around that range is good. They use an oldschool brushed motor so they are simple electronically and they will last for the sort of duty cycle we’re talking of. The sky is the limit here, no reason you can’t grab a Makita or a Fein if you want to spend the cash.
There’s a few mods you want to do to these grinders to make them happy and make them fit in a set of rollers. You need to pull the back off and clean up the wiring from the handle.
Only a few screws lets you get into the handle.
With the handle off, you can pull out the wiring.
Undo the wiring off to the capacitor.
And there ya go. Snip-snip the two wires (one neutral, one active) to the body of the grinder and you’re done. You can’t really reuse the power cord because this is double insulated cord with no earth: good idea to earth the metal body of the roller starters.
Another good thing to do with these cheap grinders is check the grease in the gearbox. Often they are undergreased. Pretty simple to check: pop off the four screws holding the gearbox cover in place.
The gearbox plate and output shaft just lifts off. Nice and simple.
Plenty of grease in this one, which is good. I’ve bought some cheap grinders before that were basically dry.
Slapping it back together and it can be good to replace the crappy screws with decent allen headed bolts. This makes them a lot more servicable: a common area of death in these grinders is the bearing at the back of the output shaft of the gearbox, if you can get them apart easily it’s way easier to sort this out and keep the grinder going.
Axles, bearing, drive options
You will need to gear down your grinder – they spin a bit too fast to be useful and you want some torque to help wind the motor over. This 2.2 kW grinder @ 6000 rpm should be making 3.5 Nm of torque, good to have more than that turning the back wheel. Common gear ratios for most 9″ grinders are between 2:1 and 3:1, with the grinder spinning 2-3x faster than the roller spins.
There are industrial gear clusters available from bearing shops, but you can also use industrial gears and chain. We like that option, especially as you can thread the inside of the gear on a lathe to directly spin it onto the thread of the grinder output shaft (usually M14 x 2). This makes replacement easy. Replacing the other one can be harder as the simplest option is to weld it straight onto your axle, but it’s an option.
Axle tech: this really depends what you want to do regarding rollers (see below) but a good option would be 25 mm or 1″ (25.4 mm) axles. Nice for weight if you can get hollow ones – you don’t need the ultimate bending strength of full rod – but either works fine.
Switch and wiring stuff