Having issues running Multiple Units

Randy Clark Apr 25, 2021

  1. Randy Clark

    Randy Clark TrainBoard Member

    Having performance issues with 3 BLI PA units running as MU. Every once in a while 15 to 20 minutes or maybe even an hour into running one of the locos makes a grinding noise in the mechanism as though one of them is locking up or hopping a tooth.

    They run very well individually and only act up when run as MU. Am I nuts or is there an issue?

    I did some research and did not find any bad reviews.
  2. DCESharkman

    DCESharkman TrainBoard Member

    It may be that they are not properly speed matched.
  3. Randy Clark

    Randy Clark TrainBoard Member

    Worked on that a little the other night before the 3rd unit showed up.

    I'm pulling the Broadway Limited and a couple extra cars.

    Do you think they need speed matched equally or have one of the A units picking up the weight and use the other A & B as helpers?
  4. Randy Clark

    Randy Clark TrainBoard Member

    I worked on the A B set which I bought first then I added the second A unit to make up an A-B-A.

    They are pulling the Broadway Limited with a couple extra cars.

    In order to balance the load I am considering taking most of the load with the rear A unit and using the A-B in the lead as helpers. Or should I just set them up speed matched with no load? When they run together uncoupled I think they run in synch with very little if any difference. I can't guarantee that but I'm going to try all 3 uncoupled here in a few minutes.

    I am kind of surprised as I also have a F7 lash up of A-B-A and they pull anything perfectly
    Last edited: Apr 25, 2021
  5. Randy Clark

    Randy Clark TrainBoard Member

    Messed up on my typing on the last post but I think you get the idea.

    Edited the previous post. Makes sense now.
  6. Mr. Trainiac

    Mr. Trainiac TrainBoard Member

    You should not be speed matching locomotives when they are pulling cars. Ideally, they should be uncoupled, running a few inches apart from each other. Speed matching when the models are coupled together adds additional confusion because of BEMF. They may seem like they are working in a consist, but as soon as they run individually, nothing is consistent. Speed match them outside of the consist, and then when you know they work by themselves, set up the consist again.

    Another thing you may want to do is to turn down the BEMF strength. Sometimes it can be too responsive and cause bucking and in-fighting as the locomotives constantly change speed and fight each other as the drawbar force changes. My most recent consist/speed matching was between two Tsunami units. My BEMF is around 100. (default/max is 255). ESU works a bit different, and I don't own any BLI, so I can't give any recommendations for this specific decoder, but it's just something you may want to test out or at least check.
    Carl Sowell likes this.
  7. Carl Sowell

    Carl Sowell TrainBoard Supporter


    I am by no means a DCC expert so take my comment with a grain of salt. I agree with Mr T's comment above. I do not own any BLI but have several KATO's that I have installed ESU Loksound decoders. In the case of ESU I first turn off BEMF then set speed on one engine, then turn BEMF back on, set aside and move to the next engine. Again, BEMF off, set CV's 2,5,6 to match the setting of #1 engine, when satisfied turn BEMF back on. BTW, one engine on program track at a time. I have a 6 unit matched early diesels that run together flawlessly. Don't worry about which one is a tad faster or slower because after you add the cars their load will smooth all out.

    Be well,

    PS: not sure your noise has anything to do with this ? ? ?
  8. 7dmack

    7dmack New Member

    I model in HO but sometimes if one locomotive is faster the slower one is running with its gears trying to slow it down instead of making it go and it will make a noise like you described. The noise can also manifest when coming down a grade with a heavy free rolling train. The traditional fix is to shim the worm gear so it stays exactly centered over the gear it is driving, remove any slop along its axis without binding it up. That's in HO anyway.
  9. NtheBasement

    NtheBasement TrainBoard Member

    Regardless of whether or not the speeds accurately match there should not be grinding noises. A loco should not grind even if it is stalled at full wheel slip. What would cause the grinding noise?
  10. Randy Clark

    Randy Clark TrainBoard Member

    I speed matched all 3 locos runnung uncoupled and got them running perfectly together but uncoupled. At most maybe an inch movement between them over a 90' long main line. I was able to isolate the problem to the "close coupling and diaphrams between the PA units. You literally have to couple them like Accumates even with Micro Trains couplers. When the locos would go through some Kato curved track sections, the bodies would mechanically jam together and cause the frame to lift and therefore the trucks would try and hop gears. Trust me, I fried a brand new PA unit when the consist came around a radius, jammed up and picked the frog on a Kato turnout a foot away from the radius.

    I have DCC Specialties overloads in the layout which have worked great for a couple years but I got distracted, walked into another room for a few minutes and when I came back the stench of melting plastic was evident.

    After this I got in my stash of couplers and assembled a pair of medium shank body mount locomotive couplers and put them on the PB unit. Immediately all the grinding and lifting of the trucks stopped.

    I am going to experiment with the recommendations of adjusting BEFM CV and see what I can come up with.

    Right now I am waiting for a response from BLI on sending the unit in for repair. The sickening part is the PA Unit wasn't even 2 days old.

    I really like my BLI locos. I have 3 - F7's pulling 18 cars like a Swiss watch right now. Perfectly speed matched right out of the box.
  11. sd90ns

    sd90ns TrainBoard Member

    Why do you assume that this is an either/or question?

    You can be nuts and still have lots of issues.
    In fact, I think it is mandatory when modeling N-Scale.
    It's certainly not a detriment.

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