DCC Loco Conversions - 12 - Dublo & Wrenn Ringfield Motor

Part 1 - Introduction

Considered as incompatible with DCC by the trade as it takes more effort than they can economically charge a customer to modify Hornby Dublo and their Wrenn loco variants despite they can run well on DCC. They have high weight, good traction mostly without relying on tyres (steam locos and diesel shunter) and were ahead of their time with relatively fine wheel profiles. The plated driving wheels generally provide good power pickup, aided by their heavy weight intended for hauling the stiff and heavy rolling stock of their time.

For brevity I will write only in terms of Dublo locomotives but this includes Wrenn versions unless there are distinct differences between them in which case I will highlight them, apart from some variations in materials I have not found any significant variations between the two.

The bulk of the conversion work is to insulate the brush holder that is fitted directly to the motor end casing thus ensuring both brush holders are insulated from track power.

Dismantling the Motor

These motors are straightforward to dismantle but a few points to consider.

1) If the original carbon brushes are to be refitted put marks on the exposed end of each brush so they can be refitted in the same holder and orientation as they have been accustomed to. This will save them having to rebed themselves during which performance is reduced and plenty more carbon dust is created to coat the commutator and motor housing.

2) If the magnet is original and healthy ensure that the armature stays within the ring magnet otherwise it's strength can rapidly collapse and need re-magnetising.

A late update: This may not be the case with a Ringfield magnet Ref 12.5.

What is a good strength for an original magnet? Well as a rule of thumb I first check the motor runs on 6V DC with the wheels off the track, the current should be about 0.25A or less. If that is okay place it on a piece of track apply power so it runs against a buffer or finger until the wheels slip (or just slip if tyres fitted), if the current limits about 0.5A then it is probably okay.

A severely weak magnet may not be enough for the motor to turn and the current will quickly rise to 0.75A or more as you turn up the voltage, which will lead to a burnt out armature winding and more cost.

If a NEO magnet is fitted this is not an issue except it attracts everything in dramatic fashion, even the ball bearing out of the motor end housing, these magnets are so strong that when fitted in an 8F even the drawbar is noticeably attracted to the loco chassis.

3) That ball bearing can also drop out if the bearing is dry, in most cases (of my locos) the adjustable bearing was in the end housing so I removed it completely, if it is the fixed type cover over the exposed bearing with tape to avoid swarf getting in and the ball bearing escaping.

4) I remove and discard all the interference suppression components and rely on the suppression inherent in the decoders.

5) There will be a small change when re-assembling the motor which I will explain in part 4.

Spare Parts

I originally attempted to obtain original spare brush holder insulators from the well known Wrenn spares seller on eBay, but as luck would have it they sold out some 5 years ago, but I expect they would have commanded a high price judging by other parts still available.

So I surfed the web from eBay to specialist suppliers for as near a fit as I could find. In practice if you are an OEM (original equipment manufacturer) you just order the design you want in the 100s of thousands, but when you only want a few then you have to use leftover or standard stock items of 50 or more with often a hefty handling / p&p cost.

I found what seemed a close enough example (Ref 12.1) which as it turned out was a high temperature black nylon shouldered washer (their standard nylon versions were not dimensionally close enough).



Although a Dublo brush holder could be fitted directly into them it was a high interference (force) fit and expanded the nylon shouldered washer too much for my liking so it would be better to drill them out so the brush holder was at most a light interference (gentle push) fit into the washer.

So after some experimentation I settled on a suitable bore and would also need to reduce the thickness of the shoulder (or flange) to a dimension similar to the original insulator on the other side of the end housing. This ensures that the brush in the modified holder was radially positioned correctly. Dimensional details are presented in the relevant parts that follow.

With hindsight it would have been more cost effective to have machined these insulators from nylon rod but having spent £24 on a minimum order quantity of 50 I decided to use them.

My Approach

I decided to use small machine tools to perform this work, it is possible to do this with a skilful and steady hand but that is beyond me, I also required a 100% success rate as these conversions are a one way operation which need to be right first time otherwise at a minimum a replacement motor end housing would be required.

Structure of this article

Most of the work is to the motor end housing, refitting the motor and adding a decoder is trivial in comparison so I cover only the Ringfield motor in this article and will follow it up with short relevant loco specific articles relating to the Ringfield motored models I have, namely Stanier 8F, Castle, West Country and diesel shunters.

Even so this article is split into multiple posts within a single thread due to the number of step by step images I will present to illustrate the process which would otherwise exceed the limits per posting on a single thread.

The next part covers the nylon shouldered washer modifications, the following two parts cover removing the original un-insulated brush holder, and finally the drilling of the end housing and refitting the brush holder with the modified shouldered washer.

The list of references is included in part 4.

Part 2 below ...

 

Part 2 - Brush Holder Insulator

The shouldered washer selected was bought from Essentra Components Ref. 12.1, it's dimensions are :-



The bore and flange dimensions required changing, initially the metal brush holder of nominal outside diameter of 4.7 to 4.8mm was a tight force fit, however this stretched the 6mm outside diameter and gave a distorted outer surface.

I decided it was best to have minimal outside distortion so that the 6mm dimension was true which required minimal interference in the fit of the brush holder into the nylon part.

To this end and to save boring you further I adopted the required dimensions shown which meant that the brush holder was a sliding to loose fit into the nylon, but compensated by drilling the end housing to 5.8mm. This allowed a slight interference fit of the nylon at 6mm into the metal hole of 5.8mm compressing it slightly, and passing on an interference fit of the brush holder into the fitted nylon part.

Modifying the shouldered washer

First step was to increase the bore, at this point it is worth having a decent set of twist drills, the ones I use are a set from Arc Euro Trade Ref 12.2 which is a 51 piece HSS set with sizes from 1mm to 6mm diameter in 0.1mm increments. Which allows one to get interference fit of parts just right, but always check the diameter of your drills with a trusted micrometer or vernier caliper, (the latter sufficient for this job) as they may not be quite what they are marked.

Gripping this shouldered washer in the chuck of my micro-lathe was a non-starter due to the chamfers on the leading edge of the jaws. So I actually mounted the bush in the tailstock drill chuck and the drill in the lathe chuck. At this time I do not have a suitable collet.

Of course it would have been easier to have machined them from rod in a conventional manner.

Drilling speed was kept to about 200 rpm, quite low, too fast would rip into the plastic and too slow dig in and rip it out of the chuck, feed was kept light, to avoid heat and jamming of the drill bit in the nylon. It would work loose a few times in the process and needed reseating but proved accurate enough for the task in hand.

The first two images show the set up. The first image below looks as though the hole is poor but I stopped in mid drill to take the picture, the finished drilling was clean cut.





Typically unless the cutting tool is very sharp the plastic will deflect a little, so not as straightforward as cutting metals but with care the desired result can be achieved.

Next to thin the flange to match the Dublo one on the opposite side of the housing. In place of an arbor I gripped a 5mm drill in the lathe chuck, the plain shank being long enough to hold it without the chuck jaws touching the flutes.

The shouldered washer with a bore of approx 4.8 mm (my 4.9mm drill bit was nearer to 4.8mm than the 4.8mm!) was pushed onto the shank of the drill (which has a useful chamfer), using a bar in the tailstock chuck such that the flange was kept clear of the drill shank.



Next at a similar cutting speed to drilling, although my micro lathe is electronically speed controlled only the top speed of 3800 rpm is marked, however as you get to understand your machine and materials you can observe how well it is cutting and whether the speeds are right.

Using light cuts of 0.2mm at a time reducing the flange thickness was easily performed with a basic tool bit, checking with a digital readout caliper as the required thickness was approached.






The finished shouldered washer was removed from the drill bit by gripping the drill in a vice with soft jaws and whilst also supporting the washer and driving it out with a small rod and light hammer.

Once a batch of shouldered washers were made it was time to start on the motor end housings.

Part 3 below ...

 

Part 3 - Brush Holder Removal

The idea of how to remove the un-insulated brush holder I found on the web (Ref 12.3) and it works well, credit where it is due.

The author also shows another way of doing this conversion without small machine tools but will require steady hands, as I was to convert some 10 motors I preferred to spend some time making up a couple of tools to aid production.

Also smaller decoders are available now so that the body of the diesel shunter may be fully re-fitted as opposed to being lifted at one end as in Ref 12.3, this I will show in a following article. Although I must admit I would have cut the space to fit the decoder.

Image 1 shows a motor end housing (the fixed end bearing version), a spare brush plug as used on other Dublo locos such as the 2-6-4 tank loco (non-insulated brush holder) and a suitable pin punch, nominally between 2 and 3mm in diameter.



Next image shows the plug fitted into the brush holder to be removed.



The next shows passing the pin punch through one holder onto the top of the plug.



In a soft jaw vice ready to be tapped out with a light hammer, most came out easily, a couple were rather tight and one just fell out when inserting the plug!



The next two show the released holder and the final position of the plug





The final image shows the separated parts.



The next stage is to enlarge the hole the brush holder was removed from.

Part 4 below ...

 

Part 4 - Brush Holder Refit

Now comes the most important part, enlarging the hole perpendicular to the axis of the motor shaft and in line with the existing insulated brush holder.

As I had a least 10 motors to modify I made up a simple jig on which to mount the motor end casing for drilling.

The flat plate is a piece of 6mm mild steel from (Ref 12.4) which is bolted to an angle plate, which in turn is bolted to the bed of the micro-mill.

Two sets of holes are drilled in the plate, two holes to suit bolting to the angle plate, and four drilled and tapped 6BA to attach the motor end housing to the plate. 6BA is the size of screws used on the motor to hold the housing parts together.

Brass screws are used to attach the housing, steel not required and the brass screws will wear out before the mild steel plate threads, the half nuts under the screw heads are just for packing instead of cutting the screws to length.

Image 1 shows the parts, including a brass alignment pin.

If the housing has a fixed bearing then tape over the bearing to prevent loss of the ball bearing and entry of dirt and swarf whilst drilling.

From here on I show the process with a removable bearing end housing.



To ensure alignment of the housing to the mill drill chuck a simple brass bar just the right diameter to pass through the original brush holder hole is reduced to 3mm at the lower end, the carbon brushes are nominally 1/8 inch diameter (3.18mm).



Once the alignment pin moves freely through both the top hole and the lower brush holder the screws are tightened up ready to start drilling, and the mill slides locked.



The housing is drilled to 5.8mm diameter at approx 1050 rpm, and 4 to 5mm deep to ensure that the 6mm diameter shouldered washer is a push fit into the resulting hole shown next.

Extra care is required with the fixed bearing type although a small groove cut into it is not a problem if drilled too deep which I was guilty of doing on the first attempt. In practice only one of the Ringfield motors I was modifying was a top fixed bearing type. Operation of the rebuilt motor was unaffected.



To ensure the shouldered washer can enter easily a relatively blunt 8mm drill is lightly applied to the hole and the drill chuck turned by hand.

The shouldered washer can then be seated on this chamfered entry and pushed into place by a square ended piece of bar in the drill chuck.



The brush holder is then pushed into place by the bar in the drill chuck, taking care to align perpendicular and the slots for the spring wire orientated correctly, i.e. parallel to the base of the housing.



The final result.



As this was a motor bought as a serviceable spare I cleaned visible debris away from the bearings, checked the armature windings were sound, each winding measured 3.2 ohm, added drops of oil to the bearings and re-magnetised the magnet which was in a poor state.

When reassembling the motor casing one of the screws must be replaced by a nylon one or the contact plate must be cut back, the image shows this plate attached to the left hand brush spring post. I prefer to fit a nylon screw.



The screws need to be 6BA and nominally 3/8 inch long, the ones I obtained from an eBay seller were 5/8 inch long and may require cropping with wire cutters after tightening, e.g. for an 8F cropping was required to avoid fouling the loco body.

For the diesel shunter trim to length before fitting by running a nut onto the screw first and trimming with a knife and then remove the nut, as the tapped hole in the shunter chassis is blind. In practice it was able to be longer than the original steel screw which is better as that offers more thread to engage the nylon screw.

Shown fitted, do not try to tighten it as much as a metal screw as they are not as strong and will twist under load particularly where it passes through the clearance hole in the end housing. But they will tighten well enough to retain the brush spring bracket, it really depends on how well the original screw hole was tapped by Hornby and of course the quality of the nylon screw.



Further information gained during re-assembling of a few locos is posted below in Part 5.

Motor End Housing Bearing Adjustment.

When reassembling a motor with the adjustable bearing in the end housing, screw in the bearing as near as possible to the original position or not quite as far, age discolouration is a good guide. As the end housing retaining screws are tightened ensure that the motor shaft retains a little end float. Once the four screws are tightened screw in the bearing until it just nips the motor shaft, I then just back it off by 1/4 turn to ensure a small end float and then run the locknut up to the housing to lock it in place.

Use of a spanner and a screwdriver together to stop the bearing from turning as the spanner is turned is advisable, otherwise over tightening onto the motor shaft will occur. Finally ensure that the required end float on the motor shaft is still present before completing the motor assembly.

What’s Next

The process described above is common to multiple Dublo Ringfield motors as a common end housing is used.

In part 15 loco re-assembly and fitting of decoders into 4 different Dublo locos which use this Ringfield motor begins.

Discussion always

Jim

Return to Index


References

12.1 Essentra Components

https://www.essentracomponents.com/en-gb

Item code: MNI-HT-M4-2

12.2 Arc Euro Trade

https://www.arceurotrade.co.uk/

51pcs HSS-Co (5% Cobalt) Fully Ground Drill Set 1.0 - 6.0mm

Item # 060-011-00150

12.3 Dublo Nutz Blogspot - DCC Conversion - How I converted a Ringfield motor

https://dublonutz.blogspot.com/2012/09/dcc-conversion-how-to-covert-ringfield.html

12.4 Macc Models

https://maccmodels.c.uk/

6mm x 100mm Bright Mild Steel Flat

12.5 Hornby Dublo Magnetiser update 2020 - Ronald Dodd

 

A late update: This may not be the case with a Ringfield magnet Ref 12.5.

This magnetiser tool is a valuable asset if you have several Dublo and old Tri-ang locomotives.

Jim

 

Amendment to part 4 - Armature windings corrected to 3.2 ohm, made the age old mistake of not accounting for the test leads at 1.1 ohm.

My digital multimeter does not have a direct zero adjustment, rather it has long winded operation setting a fixed range and using the memory function, this is a time when an moving coil meter would be quicker to use, Jim

 

Part 5 - Spring Mounting Plate Assembly

Following the re-assembly of three diesel shunters, three 8Fs and a Castle with Ringfield motors I have noticed that the spring mounting plate assembly particularly on the older models is likely to become fragile. They are made of a resin bonded paper which was widely used as an insulation material which although relatively tough, can be machined and is quite oil resistant can weaken after a few decades and crack.

If bent it is best not to try and straighten them, on one elderly 8F it was already breaking up, either from impact damage or a screw done up too tightly, the screws holding this plate should only be nipped up whether they are metal or nylon. The first image shows the broken one and the fibrous nature of the item, a substitute could be made relatively easily but I had a spare from another loco whose chassis was beyond economic repair.



This brings me to a second issue, the spring retaining pins (posts) can work loose with age allowing the contact piece which we must insulate from the chassis to rotate against the end housing, even though the screw passes through it. Tightening the nylon screw to prevent this can be impossible as the screw thread could be stripped and fail or the mounting plate split. What I have done here is apply some Duck tape to the housing such that if the contact plate does rotate into contact with the end housing it will not cause a catastrophic electrical connection for the decoder. i.e. decoder output wire making contact with raw track power.

The second image shows the tape used, and the 3rd I have highlighted it's position with masking tape for good photographic contrast only.





I mentioned in Part 4 about cutting away the contact piece as an alternative to using a nylon screw, this would have to be done very carefully to avoid disturbing the spring retaining pin or breaking the spring mounting plate, because if it comes loose the spring which bears against the carbon brush will no longer function properly.

A Mechanically Better Solution

I do not like using tape except as a last resort, but while I was re-assembling my West Country Barnstaple a much better tape free option was found.

If the contact piece can be rotated without risk to the mounting plate then it can be rotated anti-clockwise as viewed such that the solder tab can be hooked over and folded into place. I will not be using it for wiring purposes as will be seen when I describe the decoder fitting to each of the Ringfield loco types I have.

The right hand one can be just tweaked a little to do the same thing.





As a plus when the brush springs are fitted they hook over the edge of the mounting plate and stop the contact plates from becoming unhooked from the mounting plate.





In this way the contact plates are reliably restrained and no tape is required which makes this a superior and effective way of preventing a catastrophic track power short to the decoder outputs.

I will now apply this to the other locos.

 

I have added a mechanically better way of restraining the left hand contact plate eliminating the use Duck tape to Part 5 above.

 

Part 6 - Decoder Connection to Motor

The typical connection to the Ringfield motor for DC was, ignoring the original interference suppression parts :-

1) Through the chassis to the un-insulated brush holder and then via the brush holder to the brush.

2) From the pickup wire directly to the insulated brush holder and then via the brush holder to the brush.

The contact pieces being primarily for support of the interference suppression inductor and capacitor.

DCC is Particular

Any intermittent contact which may have been ignored by a loco running on DC can easily be long enough to starve the decoder of power such that it reboots, which magnifies the interruption of power to the motor. This is made worse if you have acceleration delay set up.

So I prefer to minimise the number of connections and what there are to be soldered if at all possible.

Considerations

1) connection to the contact pieces, they are only loosely gripped by the spring retaining pins, especially after decades during which slight shrinkage in thickness of the mounting plate has taken place.

Also the brush spring wire has only a sprung connection to the oxidised solder plated surface of the contact piece and the post, so at least two unreliable (for DCC) connections between decoder and motor brush, albeit they are in parallel.

2) connection directly to the brush holder, I thought that would be okay, but even on DC there was issues with one loco, running was erratic and looking closely yellow sparks could be seen between the inside of the brush holder and the carbon brush. A good clean out of tube and brush would probably fix it but for how long?

So if unreliable at times for DC a definite problem for DCC.

3) connection to the brush spring, these were not plated but are easy to solder to if any dirt is wiped off and some liquid flux is used to aid wetting by the solder.

I then use a simple hook joint to attach the decoder wire to the spring between the post and where it hooks onto the mounting plate as shown below.



By attaching there any heat by soldering does not affect the spring temper (its ability to be a spring) and also the wire does not affect the action of the spring on the brush.

This seems to be the way to go and works on the initial 8F that has been completed and one diesel shunter so far, time to track test the shunter on the layout, if all is well I will fit decoders to the other two shunters and then post about the decoder installation.