I have this engine that was one of the last RTR runs before they came DCC ready. This engine has been upgraded to DCC and the digitrax chip is on top of the motor. The problem is when the engine gets over 30 on the throttle, it starts to make a “grinding” noise and slows down. As if something is interfereing with the motor or gears. It happens in both directions, however when I take the shell off the engine works fine all the way up to 100% throttle in both directions.
Is the decoder chip putting pressure on the motor?
Could the shell be pinching the fly wheels?
Does anyone have any ideas on what could fix this?
If the noise goes away when you run with the shell off, it’s a good bet something is rubbing on the shell. There isn’t much clearance between the flywheels and the shell. Look for rub marks on the inside of the shell. Make sure all the shell mounting lugs are flash free and seated properly in the frame holes.
The motor can be out of position. Unless that rubbery pad under the motor is seated right, the motor won’t sit level, instead it will be cocked up one way or the other. This makes the U-joints run at a stiff angle, making noise. It might also push the motor up high enough to rub on the shell. Look on the bottom, all four rubbery teats on the motor pad must be showing thru the holes in the frame.
Without seeing photos of the installation, I would venture to guess the location of the decoder is being pushed down by the dynamic brake weight cage inside the locomotive. You may consider moving the decoder location to under the radiator fans by the long hood.
Not having seen the model in question I would suggest you look for a wire out of place or rubbing on a flywheel or drive shaft.
I have a GP-40, one of the later Athearn BB kits. When ever possible I avoid installing decoders on top of or near the motors.stalled On my loco I installed a Digitrax DH163 decoder behind the motor.
Just guessing, I would think your problem is interference from a wire.
After further review, and moving the decoder to that aft top of the shell. It seems that the drive shaft from the back fly wheel to the truck is slightly bent and doesn’t go all the way into the U-joint on the truck. I think that is a contributing factor.