Tuesday, October 30, 2012

HPI Cup Racer Front One Way Mods Shopping List

Here's the complete list to mod a TT-01 one way into the HPI Cup Racer. See part1, part2 and part3 for instructions. After running a pack, it's a fragile setup in that the diff gear can wander on the pressed bearing in a bearing jury rig. But, it drives so much better and the looks of the 510 are always great.

Boca Bearing
  • 2x 3x10x15mm bearings
  • 2x 3x6x10mm bearings
  • Bench vice, or similar, to press the bearing into the bearing 
  • (or 2x 3x6x15mm bearing, I couldn't find one)
Eagle Racing
  • TT-01 one way diff unit 
HPI 
  • Cup Racer ball diff bevel gear - use the stock one that's already in the car, you won't need a ball diff for drifting if you lock the gear diff in the rear
 
Dremel bits
  • Grinding stones 
    • 1x small drum grinding stone
    • 1x tapered grinding stone
  • Sanding Disks
  • Drill bit, or small Dremel bit to hog out the ball diff hole

Safety bits
  • Always wear safety goggles and a dust mask/bandana when grinding
  • It's a good idea to wear gloves when using a Dremel (mechanics gloves are great)

Modding the HPI Cup Racer for a Front One Way, part3

Some additional grinding, and the Eagle Racing TT-01 one way fits!


 widen the axle cup openings

The dogbone pins are too thick to fit the drive cups. Use a Dremel sanding disk to slowly remove material. Check often until you have a smooth fit. I ended up with a bit of slop on the pins, and will move to blades when they wear in.




 




Plunge and enlarge the center hole
After the fit is good, a new obstacle presents itself - the dogbone is too wide to fit into the axle cup. Use a tapered or other Dremel grinding stone to enlarge the cup center bore. Again, go slowly and check fit often.










check for binding before install




 nice gear mesh





Check everything for fit  before final assembly. Add a high quality grease to the CVDs to reduce friction and wear.















Sunday, October 21, 2012

Modding the Cup Racer for a Front One Way, part 2

Success! Just a bit of grinding, some bearings and there's a TT-01 one way in your Cup Racer.



I wanted to keep costs relatively low on this project, reusing parts where possible. The stock ball diff bevel gear is a near perfect ringer on the TT-01 one way. Start with the stock diff and use a Dremel to grind down the inner race lip-amajig. Once smoothish, plunge down and enlarge the opening to fit. ~12mm center bore is the goal.



The ball hole seats on the diff need to be hogged out a bit, they're set a hair too far apart. These are what are going to center the diff ultimately, the center hole only need to be mostly round and allow you to get an even fit on the screws. Reuse the three stock screws that came with the one way. Yes, they're phillips head..







Upon test fit, the gear mesh was too loose for my liking. Servicable, but needs work. Grind the diff on mounting ring slightly, you should have a good feel for this by now. I didn't measure, but it's less than 1mm.




Add blue Loctite and re-assemble. Keep one plastic washer on the driver's side (US standard) between the custom bearing and diff cup.

 




 

And that's how to mod a tt-01 one way to a HPI Cup Racer bulkhead. Of course the dog bone pins don't fit the diff cups. Part 3 - Grind the drive cupes.




Click for part1 if you missed it..

Wednesday, October 17, 2012

Modding the Cup Racer for a Front One Way, part 1




I made a bit more progress on the Cup Racer front one way tonight. I couldn't find the right size bearing, even from Boca Bearing. But with a little creative thinking and a bench vice I came up with a bearing inside a bearing.


Start by hand pressing the inner bearing - the tolerances are great, you can get a very smooth seat before pressing it with a clamp.




The Eagle Racing front one way includes two plastic shims, use one for a nearly perfect fit in the bulk head. 







I *think* this is going to line up perfectly - the measurements with my cheapo caliper makes it look good enough for metal gears.


Next step is to drill out the bevel gear center hole to fit the one way.

Click for part2..