Mounting a Generic Body Shell

[speedy_w_beans 4272]

For the most part I think Tamiya either molds dimples into their body shells or they pre-drill the holes for a specific chassis, so this makes it easy to get the correct body shell placement and line up the wheel arches with the tires for a given kit.  However, over the years I've used a number of other brands' body shells on Tamiya chassis, and of course there are no dimples for the chassis I'm using.  I've had my share of shells end up a little crooked so one side is closer to the tires than the other or the wheel arches are slightly off, and it's just really annoying.  I've even bought an extra shell from time to time to redo the work.  Anyhow, over time I've stumbled on a few key ideas and I thought I would share them here in case it helps others get the perfect body placement in the future.

For this exercise I'm using a 3Racing Sakura D4 AWD chassis with a Protoform Mazdaspeed 6 shell.  I originally bought the D4 with the intention of turning it into a throwaway/basher touring car for some street play; the AWD version includes an oil-filled gear diff, so it was cheaper in the long run to buy the AWD kit instead of buying the RWD kit and then getting the diff separately.  Since the front gear diff ended up in the back of the car (replacing the original rear spool), I filled the hole in the front with a one-way and then adjusted the center pulley and rear belt so the rear is overdriven by only a few percent.  The one-way makes the steering very crisp and eliminates some understeer relative to running a gear diff up front.  At this point the car actually has plenty of oversteer, which makes it quite fun.

The Mazdaspeed 6 shell is meant to be a cheap body; since I wasn't looking for scale accuracy or details this was a relatively inexpensive way just to put something on a chassis.  Protoform has a chart of downforce/steering characteristics for their various shells, and the Mazdaspeed seemed like a good choice (it's been popular with the racing crowd).  There are no dimples for a specific chassis, and the wheel arch cut lines are intentionally undersized to allow for different shell placement and different wheelbases.

So, here's the sequence I used to get the MS6 mounted on the D4:

1)  First, completely build the chassis, install electronics, install wheels/tires, add the battery, do some test driving, and dial in the ride height/caster/camber/toe to get the chassis set the way you want it.  For mounting the shell be sure to have the battery installed so the chassis is sitting as it normally would in use.

2)  Trim the body around it's edges, but don't trim the wheel arches.  Leave the material in place.

3)  To get the most accurate body post holes in the body, trim the posts so they only have an extra 3 holes showing.  Place the body next to the chassis, align the wheel arches with the wheels/tires, look across the hood and rear deck, and count how many holes are above the body.  Then subtract 3.  The remainder is what you want to trim off the posts.  By removing the excess length from the body posts early, you can place the body over the chassis much closer to its intended position and get the wheel arches aligned with the wheels/tires more easily.  It also means the holes you ream in the body won't be too far apart when the body is finally level.  In this photo I had already already eyeballed the posts and cut them; normally the tops of the posts would be much higher, and the rear height in particular would make the body angle forwards quite a bit.

To cut the body posts I use a small pipe cutter.  I've used a hobby knife and flush cutters before, but the result is really never quite right.  By removing the body posts from the chassis and spinning them in the pipe cutter, you get a really nice clean cut with a slight taper to it.

Result of using the pipe cutter:

4)  With the body posts cut, drop the body on top of the chassis.  The four wheels/tires did a nice job of centering the shell from side to side in this case as they just barely pushed against the material I left in the wheel arches.  All I had to do was slide the shell forwards or backwards to get the position I wanted.  Then use a Sharpie permanent marker to put some dots on the protective film, and use a body reamer to create the holes.  Drop the shell onto the posts, and adjust the body supports if necessary.  In my case I had eyeballed the body posts pretty well originally and only had two holes outside the shell both front and back.  The bottom of the shell is sitting level with the bottom chassis plate.  This is a much better "first try" result than I used to get leaving the body posts intact.

5)  With the body shell level and positioned, mark the centers of the axles on the protective film with a Sharpie.  As mentioned earlier, it's important you've already set your ride height/camber/caster/toe to your liking as this affects the position of the axle stubs.  Make sure the steering is straight ahead.

6) Now measure the diameter of the tires and make some templates using your drawing program of choice.  I just used LibreOffice Draw in this case and made some 66.5 mm diameter circles with a center cross.

7)  Cut out the templates and tape them to the inside of the shell, aligning the crosses with the Sharpie dots.  Then score the outside of the shell with a hobby knife, and snap out the arches.  You could probably use lexan scissors instead.  It's just a matter of personal preference.

8)  Finish with the usual prep and paint.  Cut the sharp corners and shape them with sand paper, and sand all the edges smooth.  Wash with dish soap.  Dry.  Mask the windows.  Paint.  Add decals.  Done!

For me the key practices include:

• Set up the chassis to your preferences first, not later.
• Cut the body posts early, and use a pipe cutter for the best result.
• Make reference dots for the wheel axles on the uncut wheel arch material, make templates the same size as the tires, and align the templates with the dots.  Then remove the wheel arch material.

I probably could have avoided buying 3-4 extra shells over the years due to mistakes if I had done it this way all along.

[Only4Fun 169]

@speedy_w_beans  Great tip about the pipe cutter for the body posts. I have some full size posts on a  Datsun 240Z Rally DF03Ra  which totally spoil the look. I have a small pipe cutter I bought for making suspension links for my Axials. Hopefully now I can make a neat job with the Datsuns posts.

Thanks mate 

[Kingfisher 1171]

For cutting the wheel arches, I have used this tool on 3 different shells now with great results. Just like what you've done, I mount the body on the posts first before doing the wheel arches. I put the needle at the center of the axle and poke a tiny hole into the shell to keep the needle in place. Then, open it up to put the blade at the top of the tire where you want the arch. Then screw it to lock it in place and make the cut for all 4 wheels without changing its position. Just remember to put the needle at the center of each axle each time. When I make the cut, I do just as if you were trimming a shell with a hobby knife. Don't push too hard, just enough to score it so that you can break it on the score line.

https://www.amazon.com/OLFA-9911-Compass-Circle-Cutter/dp/B000BK7NWC/ref=sr_1_2_sspa?ie=UTF8&qid=1538404877&sr=8-2-spons&keywords=circle+cutter&psc=1

[speedy_w_beans 4272]

Kingfisher, great idea using that scoring tool!

[Jason1145 3986]

Thanks @speedy_w_beans this will help me no end. 

Ive has a few mishaps like you with some shells and yep it’s very frustrating.

I will now cut those extra long rear body posts before trying to mark the body post holes as that is what has always caused me issues... the long rear posts causing the front of the shell to drop forward and then having to manually hold the front end up level while not letting the shell slide off kilter to the left or right before making felt tip pen marks.

I ruined an Escort XR31 shell that way a couple months back

Please dear lord, let me remember this next time I sit down with a shell!!!

( I have just yesterday cut out and fitted my HPI Zonda F shell using my old method but luckily it’s sitting true... luckily!)

[V8 Rumble 113]

This is a great tip! tires fit better in the openings.

[KEV THE REV 2319]

On 10/1/2018 at 3:48 PM, Kingfisher said:

For cutting the wheel arches, I have used this tool

I use one similar to this  , I got it from Hobbycraft  , they are awesome and fully adjustable to make any size of circle / arc needed

A great how to there Speedy WB , thanks