Fitting Knuckle Couplings




For some time, readers have been asking us to write an article on how we fit Kadee-type couplings to rolling stock. Here is that article.

"Knuckle" couplings have been available for models on the US market for many years now, principally manufactured by Kadee and Bachmann, the latter being their EZ-Mate range.

With the advent of NEM coupling pockets on British Outline rolling stock, Kadee-style couplings have become popular with British-outline modellers as a means of modelling British "Buckeye" couplings and as a replacement for the traditional "chopper" style coupling.

Fitting Kadee couplings to British rolling stock fitted with NEM pockets is normally an easy process, however, what about older rolling stock which doesn't have NEM pockets ? Worse still, what do we do about rolling stock which does have pockets, but they are mounted at the wrong height ?

In this article, we present a number of techniques which we have used on various RTR models.

Note that the author uses both Kadee and EZ-Mate and both have been found to be without compatibility problems.
Similarly, the author has had EZ-Mate couplings fitted to 48-coach trains and did not experience any breakages.

Being plastic, the EZ-Mate product tends to be about one third of the price of Kadee and they also lend themselves to easier modification. Bachmann actually supply these couplings with some of their modern-outline bulk-carrier wagons. That being said, Kadee's are ideal fittings for standard height NEM pockets.


Vehicle Types

Buckeye couplings were originally fitted to some LNER coaches, Pullman coaches, SR Bullied and Maunsell coaches and some later SR EMU's.
They were never used by the GWR or LMS who both retained screw couplings on their coaching stock to the end.

BR adopted Buckeye couplings on all coaches except some suburban coaches (such as those modelled by Bachmann) and couplings within multiple unit consists.
In order to maintain multiple unit capabilities, some BR locos were fitted with buckeye couplings in order to operate with multiple units. This was principally SR class 7x electric locomotives and Class 33 diesel electric locomotives in order to work with MKI-based EMUs and Gatewick Express formations found on that region.
Following privatisation, all kinds of couplings eventuated!

The author only uses Kadee and EZ-Mate couplings on British rolling stock where the prototype had Buckeye couplings.


Height Issues

Early implementations of NEM pockets on some models were not mounted at the correct height. This was typically overcome by manufacturers using cranked coupling shafts in order to maintain consistent "chopper" coupler heights, however, when replaced with Kadee-style couplings, everything was at the wrong height.

In this article, we cover the Bachmann MKI and MKII coaches which have this problem to this day, although this is justifiable, because to fit an NEM pocket at the correct height would require the buffer beam to be cut away which would look quite unrealistic.

There is often debate about what height a Kadee coupling should be mounted above rail head on British-outline stock modelled in 4mm scale.
The author takes the view that Kadee couplings and their magnetic uncoupling mechanisms are designed to operate at a specific height, therefore, this height (ie 3.5mm scale) should be used, regardless of whether it is "correct" for 4mm scale or not. This turns out to be the same height as that used by British RTR manufacturers.


Model Types

Kadee and EZ-Mate couplings are generally intended to be attached to vehicle bodies using a draw-box, indeed, this is how they are widely used in the US market. On British RTR models, there is a mixture of approaches. Generally, NEM pockets are fixed to wagon chassis on 4 wheel wagons and to bogies on bogie wagons and diesel/electric locos. Coaches, and more recently, some bogie wagons, have there NEM pockets attached to a chassis-mounted cam mechanism which expands when traversing curves this is ideal for close corridor connections. Note that this is a generalisation and there are exceptions.
The author uses the fitted NEM pockets.

Where NEM pockets are not fitted, the author fits couplings to bogies. There has been no performance differences between this and the RTR body-mounted implementations.


Corridor Gangways and Close Coupling

There seems to be two common ways which modellers use to achieve touching corridor connections.

One is to fit "concertina"-type gangways. With the exception of 1st generation BR DMU's, concertina gangways were never used by BR and look quite unrealistic when fitted to MKI's, II's, III's and IV's which never had them. Concertina gangways were used by the "Big Four", principally, the GWR and LMS.

The author believes that this approach is used primarily to preserve, and avoid modification to, RTR "chopper" couplings.

The other way is to pull coaches closer together. The fitting of Kadee/EZ-Mate couplings presents that opportunity. This is the method the author uses.


How to make couplings to fit models

For models which have a direct-fit NEM-pocketed coupling, we normally use Kadee NEM shank couplings without modification.

For models which have no NEM pocket, we use Bachmann Ez-Mate couplings which, being made of plastic, lend themselves well to modification.

We use the following methods for coupling fitment - Click on pictures to view in larger form:





EZ-Mate fitted to modified Bachmann Coupling.

Note the alignment of the coupling head with the original plate (marked in red).

EZ-Mate couplings are sold in three different lengths (small, medium and large) and three different shank positions (undershank, centreshank and overshank). We use Undershank on all of our installations. For the Bachmann coupling modification here, it does not matter which shank length is used because it will be cut to length anyway.

With the advent of 3D printing, it may well be possible to create an NEM fitting which better holds the EZ-Mate coupling.


EZ-Mate fitted to Evergreen strip


EZ-Mate fitted to multiple Evergreen strip for former Airfix coupling pocket


EZ-Mate directly screwed to a bogie

The following sections show the different solutions applied to various models.


Examples of fitting to models with correct-height NEM pockets

Click on pictures to view in larger form:





Nothing special here, just Bachmann TEA tankers fitted with Kadee #19 couplings. Note that this isn't prototypical - these vehicles were fitted with 'instanter' couplings or 'screw' couplings.




Hornby Maunsell coach fitted with Kadee #19 coupling.


Examples of fitting to models with incorrect-height NEM pockets

Click on pictures to view in larger form:





Bachmann MKI fitted with EZ-Mate

Note that due to the slack take up of the Bachmann coupling cam mechanism, the distance between vehicles can vary between pushing and pulling. We recommend pulling these closer together where ever possible by making the couplings slightly shorter.
If at all possible, we recommend using the 'brake pipe' couplings supplied with these coaches to couple in fixed rakes of 2, 3 or 4 coaches and to fit EZ-Mates to the ends of the fixed rakes.




These pictures show the alignment of the coupling relative to the gangway connection. We use this positioning on all gangwayed stock. The key is to have the knuckle catch proud of the gangway (marked in red).






Bachmann MKII. These use the same modification to Bachmann couplings as MKI's and they are interchangeable.


Examples of fitting to models with no NEM pocket

Click on pictures to view in larger form:





Replica MKI BG with EZ-Mate (undershank, medium) attached to evergreen strip and fitted to bogie






Airfix/Mainline/Dapol/Hornby MKIID with EZ-Mate attached to plastic fitting which fits bogie pocket




Mainline MKI Buffer with EZ-Mate attached to evergreen strip and fitted to bogie






Bachmann Thompson with EZ-Mate attached to evergreen strip and fitted to bogie








Bachmann Collett bogie with EZ-Mate (Undershank medium) attached to evergreen strip and fitted to bogie. We use the original screw hole to attach the new coupling. This is not prototypical as these coaches were fitted with screw couplings.


Lima MKII bogie with Ez-Mate coupling attached to evergreen strip and fitted to bogie. Once painted, this looks tidy








Lima class 117 DMU with EZ-Mate (undershank) screwed to bogies. These DMU's didn't have Buckeyes, so this is not prototypical.

The couplings used here are a long on the power car and a medium on the trailer coach.

Graham Plowman (2/10/2014)


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