Atlas GP7 Pahse I Problems

Discussion in 'FAQs' started by bigdonnie, Nov 30, 2004.

  1. bigdonnie

    bigdonnie Member

    I am having real problems with a GP7 Phase I CP loco that I purchased probably 18 months ago.

    When I initially bought it, I had to take it back to my local LMS after 2 days because it wouldn’t run at all. They got it running reasonably well, but it was still VERY noisy.

    It has sat in the box since that time, but I took it out again on the weekend because I’m finally wiring the control panel to my coffee table layout.

    Here’s the main problem I’m experiencing --- basically, it either does not run or needs a lot of ‘coaxing’ (ie pushing) to get it running at voltages up to approx. 8 volts. It runs fine at higher voltages, although it is by far the noisiest N or HO loco I’ve ever owned! :mad:

    Any suggestions? I am reasonably mechanical, so I’m quite comfortable trying to get it to run better as long as I know what I should be focussing on to try and determine the root cause.

  2. moria

    moria Member

    Hi Donnie :)

    Not sure if your talking about N or HO here for your GP7, but if N-gauge I picked up the following tip after re-assembliung one of mine after decoder fitting...

    These locomotive are known to be very loud after you reassemble them, and
    they sound like a coffee grinder. On all of mine I have removed the inner
    most thrust bearing on each side of the motor. After doing this they are
    absolutely whisper quiet.(a Ron Beardon tip picked up on the Atlas forum)

    Your mileage may vary, and if your talking HO I have no clue.

    PS.. if you do this and yours go wrong, please don't hold me responsible :)


  3. bigdonnie

    bigdonnie Member

    Sorry --- I was originally going to post this in the N/Z forum.

    It is an N scale loco, so (i) I will try your suggestion and (ii) I won't hold you responsible if it no longer runs after I do this ;)

    While I'm in there trying that, maybe the source of my electrical problem will become evident as well.
  4. bigdonnie

    bigdonnie Member


    I assume the thrust bearings you are referring to are the two plastic pieces on either side of the fly wheels (see image)? Just want to make sure before I take the inner ones out as per your tip. Thanks

    Attached Files:

  5. moria

    moria Member

    Hi donnie :)

    Yep.. heres the origional pictures from Ron's site...

    Before mods...




    Best access is to remove the hex nut that fits in the flywheel and then slide the bearing off the shaft. I found the best way to remove the hex nut was to get a bit medieval on it and just hold it tightly, twist slightly and pull using fingers only.. no tools.. it then popped off no problem, just a bit of nerves on my part to do it :)

    If you are nice and careful, if it doesn't help, you can always put the thrust bearing back :)


  6. bigdonnie

    bigdonnie Member

    Seems simple enough --- I'll let you know how I make out.

    On the electrical side, I think the issue is just a pickup problem since the drive mechanism seems to work smoothly throughout the voltage range. The actual contact area seems to be ridiculously small, so I'll clean everything up and see what happens. I'm also thinking about what I can do to increase this contact area.
  7. bigdonnie

    bigdonnie Member

    Much Better!


    I removed the inside bearing blocks last night without any problems and it significantly reduced the noise from the engine --- I wouldn't call it 'whisper quiet', but its good enough for me. Thanks for your tip about how to take off the hex nut --- not having to worry about whether or not I would damage these made the job a snap quite frankly.

    I'd like to make a couple of observations about the drive of this engine based on my experience from doing this fix last night. It doesn't surprise me at all that the drive on this engine is noisy. First, the brass(?) worm gear teeth are very rough when you look at them under a magnifing glass. Second, the gear set in the trucks has alot of slop in them. IMHO, taking out the two bearing blocks allows the worm to move sideways in either direction to compensate for both of these problems rather than trying to 'eat' the pimary plastic gear whenever there is a slight mismatch.

    This is a perfect example of why plastic is not the right material to use for small drive gears. Yes, they're inexpensive, but in this case they contribute to a very mediocre drive train. There at least two zinc diecasting companies in Canada and the US that specialize in producing very small, high precision components at moderate cost. They both can make small gears to an AGMA 8 spec (10 is 'perfection' and is never achieved in a mass production environment). I would hate to guess to what tolerance the plastic gears in this loco's drive train are made --- 5 or lower I am guessing.

    Yes, I realize that all MRR manufacturers including Atlas need to keep their costs down. However, I would prefer to pay $5-10 more for an engine with a precise, quiet drive than having to take my time to figure out this type of problem (even though I must admit I enjoy doing so :) )

    I'll get off my soapbox now.................:D

    Thanks again for the assistance Graham.

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