This is the large spur gear cover which is compatible with the TRF201/TRF211 4 Gear Short Laydown Gearbox conversion only (
http://shpws.me/RG6F). It is not compatible any of the CTE RC 3 gear transmissions.
This cover fits by removing the Yokomo motor plate and the spur cover spacer, fitting this cover in place of the spacer and re-fitting the motor plate over the top. The motor plate screws hold it in place. It fully encircles the spur gear from the top to the underside of the motor plate, and works with spur gears up to 80t. This not only offers more protection for your body shell, it helps prevent dirt, sand and other foreign objects gettings into the spur gear. There are also two mounting tabs which can be threaded with an M3 tap. You can fully enclose your spur gear by adding a front plate (
http://shpws.me/R87P)