99995: Motors from Blacque Jacque showroom, Sport Tuned in an SRB

Model: (Click to see more) 99995: Motors
Status: How To Guide
Date: 25-Jun-2007
Comments: 5

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Where to remove material to make a Sport Tuned motor fit the SRB gearcase and retain the original motor cover.
Essential tools:
Permanent marker.

Three sided bearing or engineers scraper, or a Dremel with a sanding / abrasive wheel.

Calipers are optional but handy.

The RS540 Sport Tuned motor is usually around 35.5mm diameter at the front of the can with a 13mm diameter front bearing, most SRB gearboxes are slightly less than this. Modern silver cans are the same can size as the ST & therefore don't often fit the gearbox.

Both gearboxes in these photos started out around 33.2 to 33.3mm dia for the motor recess.

First, identify whether you have a 2 or 3 lug gearbox (3 lug after modification, fig.7). If the right hand gearcase has 2 small pins, there is only a little work to make the Sport Tuned fit.

If it has 2 pins plus a larger lug, the lug must be removed first. The ST will fit correctly over the 2 pins & the leadwire exits will line up correctly with the motor cover.

Cut off the large lug (if present) & sand or scrape flush to the bottom. Once the large lug has gone, it usually just needs a little material removing from the small lip near the idler gears and a little work on the front motor bearing hole.

Colour the sides & bottom of the motor hole with the permanent marker, scrape a little metal off with the bearing scraper & test fit the motor. Keep repeating these 3 steps until the motor becomes a 'sticky fit'.

At this point you may also be binding up on the front bearing hole, notice paint being scraped off during the test fittings & use this as a guide to where you should remove more.

Once it becomes a looser fit, ensure it's bottoming out fully in the hole, the scratch mark near the magnet retaining tabs is 15mm from the front face (fig.4), the exact depth of the RH gearcase.

The trick is to work slowly & methodically, removing small amounts to make it a slight push fit.

Once complete, the pins will prevent the motor spinning in the case & the slight pressure from the motor cover will keep everything in place, just as Tamiya intended with their original design.

Comments welcome as always.