BLI P70 - Correcting Coupling Distance How-To

[cbroughton67]

If you've been following the discussion about the new BLI N-scale PRR P70 coaches in the Product Discussion group, your'e probably aware of the excessive coupling distance between cars. What follows is my approach for body-mounting Micro-Trains 1016 couplers on these P70's and reducing the coupling. 


First, this is the stock coupler setup. The coupler box is mounted to a pivot mechanism that allows the coupler box to swing from side-to-side, in addition to the side-to-side movement of the coupler itself.



This photo shows the area after the pivot cover and coupler setup have been removed.



The first modification is the shave-off the ridge seen on the left side of the opening in the previous photo. You can see where it has been removed in this photo.



Next, I use a piece of Evergreen strip, 0.020" x 0.250" by about 3/8" long to fill the opening. You'll notice that shaved a bit off of the left-end to remove the "hump" where the ridge was shaved away.



This is the top view of the styrene strip. I cut a shallow "V" in the end of the strip to accommodate the raised "V" on the car, and to allow the outer edges to rest on the slight ledge on either side of it. The styrene is glued in-place with Plastruct cement, both on the underside and on this little ledge.



Next, reinstall the original pivot cover.



Now, cut a piece of Evergreen strip, 0.030" x 0.250" by about 1/8" long and cement it in-place on the first styrene strip. It should sit flush with the shaved area immediately to the left. This is the surface where the 1016 will be mounted. Don't drill the hole just yet...



The coupler box should rest flush with the outer-edge of the pivot cover. Mark the screw hole for the coupler with a scribe, make sure it's centered on the car's centerline, then drill and tap for a 00-90 screw. I used 3/8" flathead 00-90's for this install. 



Before reattaching the body shell, you'll need to shave-off the area just below the diaphragm to provide clearance for the coupler. Shave it flush with the bottom of the diaphragm where it attaches to the shell. Also, make sure the coupler trip pin is flush with the top of the knuckle, so it doesn't interfere with the diaphragm.



Here's the completed install:



Coupler height is maintained.


Just for comparison, here's the "Before" shot...


And finally, a much-improved coupling distance!


My solution for the obnoxious interior lighting was much simpler. I removed the light boards!

I hope this helps! Enjoy!
Chris Broughton

[wcfn100]

Only BLI would include a kinematic coupler to preserve the 7' car spacing around curves. 


Jason

[Philip H]

So, whats the minimum radius on these babies post surgery?

[wazzou]

Nicely detailed explanation Chris. 
I don't have a dog in the hunt, however it does appear that you could even make the distance shorter, yes? 
Or, did you try that and determine this was the closest you could get it?
On a different note.  I'm curious of the method/s you employ to determine the centerline of the underframe to scribe and drill your hole.
I find myself doing that from time to time, with good result but I am often left thinking there has to be a better way.

[cbroughton67]

So, whats the minimum radius on these babies post surgery?

I don't think I have any track with a tight-enough radius to really check. Still pretty tight, I believe.

[cbroughton67]

Nicely detailed explanation Chris. 
I don't have a dog in the hunt, however it does appear that you could even make the distance shorter, yes? 
Or, did you try that and determine this was the closest you could get it?
On a different note.  I'm curious of the method/s you employ to determine the centerline of the underframe to scribe and drill your hole.
I find myself doing that from time to time, with good result but I am often left thinking there has to be a better way.

Yes, I could have tightened it up a bit more, but these seemed good enough. The opening in the pivot cover between the coupler box and cover could be widened just a couple of thousandths to let the coupler box slide back a bit more. I've completed one car using this technique, so maybe I'll try that on the other cars.
As for centering the mounting hole, I use "dead reckoning" more often than not. I'll hold the scribe in the initial mark, sight down the length of the car, and adjust as needed. If I'm working a several similar cars at a time, I sometimes make a jig to locate the mounting hole.
Chris

[wcfn100]

It looks like you could just change the factory coupler with something shorter, and still keep the kinematic movement. 

Jason

[cbroughton67]

It looks like you could just change the factory coupler with something shorter, and still keep the kinematic movement. 

Jason

I considered that at first, but because of how it's designed, the coupler would end up being too low. This method maintains the correct coupler height.

[learmoia]

 

So not only do they design the car to operate on a 9" radius, they over engineer the coupler to (try to) be able to couple on a 9" radius.

 

Similar to the solid stock car.. 'to act as a speaker enclosure'.. only to find ANOTHER speaker enclosure inside the car..

~Ian

[davefoxx]

If someone wants to close the gap further, you could use @cbroughton67's method but substitute an MT 1015 (short shank) for the MT 1016 (medium shank) that he used.  You might have to lose the trip pin, but I always cut those off anyway.

DFF

[chicken45]

@cbroughton67 you should post the "before" pic.

[randgust]

It would appear like you could even mount the box a little further back if you wanted to, unless the wheels or trucks are banging into it.... do you have a photo of the finished install from the bottom?

I've been really surprised how well the body-mounts work on the MT heavyweights, as long as you don't mix them with truck mounts, and that they will handle an 11" curve if they have to.

[peteski]

It looks like you could just change the factory coupler with something shorter, and still keep the kinematic movement. 

Jason

Yeah, it would have been nice to mount the coupler even closer to the car end while retaining the Kinematic feature (which is specifically designed to extend the coupler reach on curves).

What a weird design!  Kinematic mechanism is specifically used to allow for close coupling, even on sharp curves, yet BLI still utilized extra-long-shank coupler.     Boggles my mind. Seems  like the coupler area was designed by 2 engineers not actually talking to each other.    One included the Kinematic mechanism, while the other one added that mile-long-shank coupler!

Like I mentioned in the other thread, BLI should have an experienced "real" model railroader vetting the design for boo-boos like this before going into production.

Sill, thanks for the how-to procedure Chris.

[cbroughton67]

@cbroughton67 you should post the "before" pic.

I added it to the OP.

[Maletrain]

Wondering if BLI went to the longer shank after finding that their kinematic design did not succeed in getting their cars around their intended minimum radius curve.  Whatever, it seems a shame to make the effort to produce a very prototypical car of a particular type, and then make it have a very toy-like coupling distance.