XR311 Torsion Bar

The most delicate parts for XR311 model number 58004 and Cheetah model number 58007 are the two front torsion bars and the two rear torsion bars, which are made of black plastic and are virtually impossible to find new on the market. The XR311 re-release is equipped with a different type of torsion bar. This new solution, which involved a modification in the suspension arm attachments, does not allow for perfect interchangeability with the original model.

Original version:

A – plastic torsion bar
B – torsion bar stiffness adjustment pawl

Re-release version:

C – metal torsion bar
D – spring lock system
E – torsion bar stiffness adjustment pawl

In the event of a breakage, there is only one alternative: rebuilding the part.
It is highly likely that the torsion bar will break with the square pin stuck inside the suspension arm. It is possible to extract the broken square pin inside without damaging the suspension arm.
The following sequence of pictures shows the procedure for extracting the broken torsion bar pin from the suspension arm:

1 – Prepare a drawing paper clip or wire with a diameter of 1…1.5 mm
2 – Heat one end with a lighter or the kitchen fire
3 – When the iron turns red is ready, insert the red-hot tip into the centre of the square pin, taking care not to damage the seat or go through the suspension arm itself
4 – Wait for the iron to cool down
5 – Pull out the iron and the torsion bar piece, which look like a single piece because they are welded together

Reassemble the torsion bar, which is formed by the split piece that was just extracted and the torsion bar itself. The following picture shows the two separate parts and their measurement, despite parallax errors the measurement is approximately 100 mm. The picture shows the front torsion bar.

List of materials required for the repair

A – styrene square section bar 3 mm side
B – styrene strip 0.3 mm x 3 mm section
C – styrene sheet 3 mm thick

The following sequence of pictures shows the procedure for rebuilding the front torsion bar:

1 – cut a square section bar of 3 mm side 100 mm long
2 – to reconstruct the part highlighted in the hole, the spring block; drill a 3 mm diameter hole in the 3 mm thick sheet

3 – check that the 3 mm square-section bar enters the hole with difficulty
4 – cut out a first square from the sheet with the hole in the centre, the side of the square must be at least 10 mm long
5 – reduce the size of the square by working with sandpaper, take the dimensions of the square on the torsion bar you are replacing as a reference
6 – using acetone, weld the square at the correct distance from the end of the new bar, taking the starting bar as a reference

7 – the square section of the original torsion bar has different dimensions; on one side the side of the square is 3 mm on the other side the side of the square is 4 mm. From the strip with a cross-section of 0.3 x 3 mm, prepare four strips with the same length between the square just welded and the end of the bar. They serve to change the side of the square of the section from 3 to 4 mm
8 – where indicated by the arrow, weld the first strip to one side of the bar with acetone
9 – turn the bar 90° and where indicated by the arrow, solder the second strip with acetone
10 – turn the bar 90° and where indicated by the arrow, solder the third strip with acetone

11 – rotate the bar 90° and where indicated by the arrow weld the fourth strip with acetone.
12 – check that the new bar fits perfectly into the suspension arm (3 mm square section side) and the adjustment pawl (4 mm square section side, detail shown as “G4” in the picture below).

If there are gaps, proceed as shown in the following picture sequence; weld 2 additional strips on two adjacent sides; as shown in the picture with the green and red line.

The same steps below can be done for the rear torsion bar, the only thing being to change its length in step 1.
Apply TS82 rubber black paint to the plastic.

For the adjustment of the torsion bars Tamiya has provided a system that is as simple as it is ingenious; there are two steps to be performed:

A – Press the pawl along the red line, so as to unlock the pawl and allow it to rotate; the rows must come completely out of their seat.
B – Turn the bar clockwise or anti-clockwise, yellow line, so as to adjust the stiffness of the suspension.

At this stage check that the bar has the correct length, if it is too long the adjustment pawl will not disengage so proceed to shorten the torsion bar by working one end with sandpaper.

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