B2 Prototype Replica Assembly Manual

PHOTOS COMING SOON!

 

Thank you for purchasing the Moto-Obscura B2 Prototype Replica Conversion kit!


This kit requires some modifications to be performed in order to install it on your B2 chassis. These modifications are outlined in this document. If you have any questions or concerns, please do not hesitate to reach out to Moto-Obscura’s social media messenger accounts, or by email to nick@moto-obscura.com.


Included components:

1x Aluminum Bottom Chassis Plate

1x Nylon Top Brace

2x 4-40 x 5/8” Flat Head Screws (shock tower to top brace)

4x 4-40 x 1/2” Flat Head Screws (arm pivots)

6x 4-40 x 3/8” Flat Head Screws (bottom plate to chassis & trans bottom screws - rear)

2x 4-40 x 1/4” Flat Head Screws (top brace to transmission case)

2x 4-40 x 3/16” Flat Head Screws (transmission bottom screws - front)

2x 4-40 x 1/4” Button Head Screws (rear of bottom plate to motor plate)

4x 4-40 x 1” Socket Head Screws (transmission to motor plate)

2x 4-40 Aluminum Washers


Not Included but Required for Installation:

1x Stealth Transmission

1X Stealth Motor Plate


Tools Required:

Safety Glasses

Center Punch (or a nail and hammer)

1/16” Hex Driver

5/64” Hex Driver

Utility Knife

Xacto Knife

Permanent Marker

Dremel or Similar Rotary Tool with Cut Off Wheels suitable for Metal, and a Grinding Tool

Sandpaper / Files

Drill or Drill Press

1/4” Drill Bit

#47 (5/64”, or 2mm) Drill Bit

 

 

Transmission Case Modification:

A Stealth Transmission case will need to be modified in two areas: First, a notch will need to be cut into the middle of the forward front of the case to allow the top brace to interface with one of the 1” socket head screws. Second, the bottom of the transmission case will need to be narrowed to fit between the B2 rear arm pivots.

 

  1. Wrap a piece of tape around a 1/4” drill bit, 1/16th of an inch from the tip. This will be your drill stop marker. Using a hand drill or drill press, drill a counterbore inside each transmission case half on the front upper screw hole to the marked 1/16” depth. Work carefully and at your drill’s slowest setting. The Nylon material will have a tendency to grab the drill bit, making it difficult to stop it from plunging deeper than desired.


  1. From the edges of the holes you just created, mark straight up to the edge of the transmission case, and straight forward, as shown in this photo. You will remove all of the material between the lines to a depth of 1/16” using a utility knife. Take great care not to cut yourself. Place the transmission case halves on your work surface and press the blade down into the transmission case, not towards your hand. Once material is removed on both transmission case halves, test fit to ensure the tang on the bottom of the top brace fits inside the slot you’ve created, while allowing the case halves to properly mate together without a gap between them.


  1. Install the B2 rear arm pivot blocks (not included) into the aluminum lower plate using the four included 4-40 x 1/2” flat had screws. You will need to trim the lower portion of the transmission case to fit between the rear arm pivots as shown in the photos below. Having the pivot blocks installed will allow you to check fitment of the transmission case once you start trimming. Trim off the front transmission mounting holes and taper the lower portion of the cases with a utility blade. Work slowly and check fitment frequently to ensure that the cases sit flush against the lower plate, and that the two rear transmission mounting holes line up with the holes in the plate.


  1. Once the transmission fits flush against the bottom plate, mark the center points of the two forward transmission mounting holes with a fine tip permanent marker. Drill these two holes into the transmission case using a #47 drill bit, then remove any burs inside of the case with an Xacto knife. This concludes the transmission case modifications, take a deep breath and admire your work!


Motor Plate Modifications:

The Stealth motor plate (not included) will also need to be modified to fit the B2 chassis. For these modifications, an adhesive backed cutting template has been included.


  1. Apply the cutting template to the motor plate. Be sure the two larger holes line up closely with the original screw holes on the back of the motor plate. Trace the outline of the cut template with a permanent marker, as well as the two small holes.

  2. Always wear safety glasses when using power tools. Carefully trim along the cut lines using a Dremel or similar rotary tool with a thin metal cutting blade. It is advisable to take smooth shallow cuts, repeating until the blade passes through the entire thickness of the material. Be careful not to apply excessive pressure or the blade may “grab” and cause the tool to jerk violently, potentially leading to motor plate damage or bodily injury.

  3. Using a center punch, or a nail and a hammer, punch the center of the two small permanent marker dots that were marked from the template. Drill two holes at these locations using a #47 drill bit (5/64”, or 2mm), then tap the holes with a 4-40 thread cutting tap.
  4. Wrap a pair of pliers with several layers of tape to prevent it from marring the anodized finish on the motor plate. Carefully clamp down on the back portion of the motor plate as shown, and bend the tab in towards the front of the plate. The angle is not important at this point, and will be adjusted during assembly.

 

Assembly:

  1. Install rear arm pivots to the aluminum bottom plate using four included 4-40 x 1/2" flat head screws.
  2. Assemble transmission internals and close the transmission cases. Insert the bottom tang of top brace into the slot in the transmission case and fix the brace to the cases using two 4-40 x 1/4" flat head screws in the two top holes. Attach the transmission assembly to the motor plate using four 4-40 x 1" socket head screws. Be you have added the four black plastic spacers between the transmission case and motor plate (note: some aftermarket or re-release transmission cases have the spacers build into the right side case half).
  3. Attach the motor plate/transmission assembly to the bottom plate using two 4-40 x 3/16" screws threaded through the two holes in the back of the bottom plate, into the back of the motor plate. Ensure the motor plate is aligned straight with the bottom plate and tighten the two screws.
  4. There may be some space between the bottom of the transmission and the bottom plate, and you may find that the holes in the transmission don't quite line up with the bottom plate holes. This is normal, and can be solved by slightly bending the rear of the motor plate and the bottom plate until the holes line up. This can be easily done by holding the transmission/motor plate assembly in one hand, the bottom plate in the other, and gently pressing forward on the rear of the bottom plate and motor plate until the parts line up.
  5. Once alignment is close, install two 4-40 x 3/8" flat head screws into the rear bottom transmission case holes. As you tighten these screws, everything should pull together. Next, install two 4-40 x 3/16" flat head screws into the forward bottom transmission case holes. Be sure not to over tighten, as the short screws will easily strep the transmission case holes. Only tighten to snug, so that the screws are flush with the bottom plate.

 

Installation Onto Chassis:

With the rear end fully assembly, it can now be installed onto the chassis as a single piece. Slot the assembly into plate at the rear of the chassis and secure the bottom plate with four 4-40 x 3/8" flat head screws. Secure the top brace to the rear of the chassis through the rear shock tower using two 4-40 x 5/8" flat head screws.

Assembly and installation is complete! Enjoy your Moto-Obscura B2 Prototype Replica! Remember, since a 2.25:1 transmission is now being used, your pinion to spur gear ratio should be adjusted respectively.