21mm gauge wheel sets for IRM Park Royals and Mark IIs

[lucas]

A couple of weeks ago, while browsing the forums well after my bedtime, I half jokingly asked how difficult it would be to have some aftermarket wheel sets made to regauge the upcoming IRM Park Royals.

On 29/4/2026 at 1:22 AM, lucas said:

Looking at the pictures shared earlier it does look like much the same setup as the Mk2s. Makes me wonder how difficult it would be to get a factory to run off a small batch of 21mm split axle wheelsets

The Park Royals use split-axle wheel sets similar to the Mark 2s for electrical pickups for the interior lighting. This has the side effect of making them a bit of a pain to regauge.

To answer my own question, I did a little digging and found a guy who's happy to run off a small batch of wheels for a half decent price.

So would there actually be enough interest to justify producing some wheels?

They would 12mm diameter EM profile wheels set to 19.3mm back-to-back on a 28mm long 2mm diameter split-axle. I know this is not ideal for those using P4, but I guess it's better than nothing? From what I can tell 21mm EM seems to be more popular (and it's also selfishly what I'm using).

These will be designed to fit the Park Royals when mine arrive. They should also fit the Mark 2s, I don't see why they wouldn't, but I don't personally own any to test with. If someone can send me a few measurements of theirs to double check it would be much appreciated!

The cost should work out to around €9-€10 per coach (set of 4 axles), depending a little bit on how many I order and what I end up getting charged for import tax.

So, I'm trying to gauge interest to see if anyone else would want a set. I'm happy to take on the risk of ordering the wheel sets, but only if I can be somewhat sure I will sell them.

Please reply below or send me a PM letting me know how many sets you would want for either the Park Royals or Mark 2s. This is purely to get an idea of numbers, I'm not accepting pre-orders. I don't want to take anyone's money until I have the wheels in hand. But on the off chance I run out, anyone who expresses interest now would get priority.

 

EDIT: The Park Royals turned out not to be that difficult to regauge, see mine and Mol's posts below

Edited 6 hours ago by lucas

[Mol_PMB]

This sounds like an excellent plan - thank you for taking the initiative!

Somewhere I think I have a spare pair of IRM B4 bogies from the first batch of Mk2s that I could measure up, if that would help? No guarantee the wheelset interface is the same as the Park Royals of course.

Potentially I would be interested in enough for 20 coaches. 
I’m in GB so if there was a way to avoid getting taxed twice that would be advantageous!

Cheers,

Mol

[murphaph]

Is it not possible to just push the wheels out like other IRM bogie stock? I never really looked closely at the Mk2 bogies. Just assumed they could be pushed out like the 42' flats etc.

[Brendan8056]

The IRM (and the latest batch of Murphys AC stock) are easy coaches to regauge to 21mm. See the pic, which shows the difference. I did not worry about removing the brakes on my IRM ones, they were only for show anyway!

I feel sure the same design would be used on the Park Royals, why change something when it works well.

A supplier of 28mm length axles could be useful for rebuilding the older Murphys AC stock and the Craven bogies. I make my own 28mm axles but some may not wish to do this.

[Horsetan]

7 hours ago, lucas said:

.... did a little digging and found a guy who's happy to run off a small batch of wheels for a half decent price.

So would there actually be enough interest to justify producing some wheels?

They would 12mm diameter EM profile wheels set to 19.3mm back-to-back on a 28mm long 2mm diameter split-axle. I know this is not ideal for those using P4, but I guess it's better than nothing? From what I can tell 21mm EM seems to be more popular (and it's also selfishly what I'm using)....

I only work to P4 standards, so I wouldn't be in the market for these.

Bear in mind that both the Mk2 and the Park Royal bogie wheels are based on a 1mm/1.5mm dia stub axle, and the "live" pinpoint bearings are matched to this. A 2mm diameter pinpoint does not work properly in the IRM bearings as the angle of coning is different - this was the first thing I tried, using Scalefour Society 28mm axles, and found that a 2mm pinpoint results in significant rolling resistance / dragging.

P4-profile coach wheels commonly come on a 2mm axle, so that means finding a suitable converter bush to press into the wheel centre to reduce it to 1mm/1.5mm. Bushes of that kind are very hard to find. Most 1.5mm i/d bushes on the market have an outer diameter of 2.4mm so cannot be pressed into a standard P4 coach wheel.

IRM list their pinpoint stub axles as spares in the coach instruction leaflets but whether they are actually available is another thing altogether.

[lucas]

On 15/5/2026 at 3:29 PM, Mol_PMB said:

Somewhere I think I have a spare pair of IRM B4 bogies from the first batch of Mk2s that I could measure up, if that would help? No guarantee the wheelset interface is the same as the Park Royals of course.

If you could get some measurements of the wheelset and the bogie that should be great! Just to double check; wheel diameter should be 12mm, axle length should be 28mm, and there would need to be >~24.5mm space between the frames. And you wouldn't be able to get an accurate measure of the cone angle on the axle pinpoint?

I'll get the measurements for the Park Royals when they arrive here, and take it from there.

On 15/5/2026 at 3:29 PM, Mol_PMB said:

I’m in GB so if there was a way to avoid getting taxed twice that would be advantageous!

I don't think there is an easy way to avoid that unfortunately. As far as I know I can't deduct VAT the way a business can. I had thought about splitting the shipment (sending half to Ireland and half to the UK) but we'd end up paying shipping twice in that case and for a small order it's actually a good chunk of the overall price. So that really wouldn't end up being any cheaper in the end.

 

19 hours ago, Brendan8056 said:

The IRM (and the latest batch of Murphys AC stock) are easy coaches to regauge to 21mm. See the pic, which shows the difference. I did not worry about removing the brakes on my IRM ones, they were only for show anyway!

I'd read quite the opposite in a few places. Something about the sleeve being what maintains the proper gauge in OO. Also the difficulty in moving metal wheel on metal axle, unless you have the proper tools to do that.

 

17 hours ago, Horsetan said:

Bear in mind that both the Mk2 and the Park Royal bogie wheels are based on a 1mm/1.5mm dia stub axle, and the "live" pinpoint bearings are matched to this. A 2mm diameter pinpoint does not work properly in the IRM bearings as the angle of coning is different - this was the first thing I tried, using Scalefour Society 28mm axles, and found that a 2mm pinpoint results in significant rolling resistance / dragging.

I wonder if it's the 2mm axle or the pinpoint angle that causes issues? or both? I know some axles are made to 55° angle while others are 60°. Could it be that the bearing expects a 55° angle while the axle is 60°? It would be ideal if a 2mm axle could work with the correct cone angle.

[Horsetan]

22 hours ago, Brendan8056 said:

The IRM (and the latest batch of Murphys AC stock) are easy coaches to regauge to 21mm. See the pic, which shows the difference. ....

Pushing the IRM stub axles out on the insulating muff results in quite a wobbly wheelset, as there's little grip left.

[Mol_PMB]

7 minutes ago, Horsetan said:

Pushing the IRM stub axles out on the insulating muff results in quite a wobbly wheelset, as there's little grip left.

Presumably the length over the pinpoints is then also too long?

is it possible to shift the wheels on the stub axles? 

[Horsetan]

10 minutes ago, Mol_PMB said:

...is it possible to shift the wheels on the stub axles? 

The wheels are force-fitted on the stub axles, so the only way of shifting them is with a proper press tool. If you take the expedient route and try to hammer it from the pinpoint end, you may well end up blunting the pinpoint, which will result in detrimental running.

A new IRM stub axle, and a new wheel is the best solution, but I don't know if IRM's Chinese contracting factory keeps stocks of 1mm pinpoint axles for spares purposes. They are certainly listed as spares and even have parts references, but that's not the same as actually being available to purchase. 

[Mol_PMB]

Just now, Horsetan said:

The wheels are force-fitted on the stub axles, so the only way of shifting them is with a proper press tool. If you take the expedient route and try to hammer it from the pinpoint end, you may well end up blunting the pinpoint, which will result in detrimental running.

A new IRM stub axle, and a new wheel is the best solution, but I don't know if IRM's Chinese contracting factory keeps stocks of 1mm pinpoint axles for spares purposes. They are certainly listed as spares and even have parts references, but that's not the same as actually being available to purchase. 

Thanks. And since almost all replacement wheels will suit 2mm axles, it's not an easy fix.

I'll try and find my pack of B4 bogies tomorrow and have a closer look and a measure.

[Horsetan]

10 minutes ago, Mol_PMB said:

Thanks. And since almost all replacement wheels will suit 2mm axles, it's not an easy fix...

The ideal solution would be a 2mm o/d bush pressed into the new wheel and bored 1mm/1.5mm for the stub axle. That's the only way of retaining the original "live" function for lighting and other things.

It's not meant to be easy. When Rapido started doing RTR OO, it was quite clear that it had been designed to prevent people from tampering with the model, so rewheeling to a wider gauge was very difficult indeed or virtually impossible.

Edited May 16 by Horsetan

[DJ Dangerous]

3 hours ago, lucas said:

I'd read quite the opposite in a few places. Something about the sleeve being what maintains the proper gauge in OO. Also the difficulty in moving metal wheel on metal axle, unless you have the proper tools to do that.

I’ve been following this thread with a mix of curiosity and fear.

Would you mind posting some of those links, please?

 

19 minutes ago, Horsetan said:

The wheels are force-fitted on the stub axles, so the only way of shifting them is with a proper press tool.

So with one of THESE, a cheap wheel puller, the IRM wheelsets are easy to re-gauge to 21mm?

[Mol_PMB]

I have a wheel puller and I have made some extra tools for it including a hollow-tipped one so that I can push on a pinpoint without blunting it. 

However, the non-insulated IRM wheels on 2mm axles are very hard to shift. I can do it, but if the ones on 1mm axles are as tight a fit then I'd be wary of bending the thinner axle. 

I tend to discard the IRM wheels and replace them with EM profile wheels as the IRM wheels have a surprisingly coarse profile. I guess that's to suit a wide range of OO track standards, but it's not ideal for EM. I put the EM wheels on the IRM 28mm axle once I've pushed the old wheels off. That's OK when the axles are 2mm diameter but doesn't work for 1mm axles. The EM profile wheels I use are insulated so would not be ideal for lighting pickups either. All these problems can be solved but it's a faff, hence the attraction of getting a batch made up of exactly what we're after.

[Brendan8056]

If it helps I use this for doing my 21mm gauge wheelsets now. It is superb, and costs the same as in Germany, as the manufacturer deducts the VAT for export to the UK. He responds very quickly to enquiries in perfect English. Until I purchased this I was using the hammer method.

https://www.fohrmann.com/en/wheel-spacer-h0.html

As for wobbly wheelsets, I have had a few go like that with the IRM bogie wagons,, and a couple wrecked and replaced by spare axles from IRM bogies purchased on their own. The non insulated wheelset is a very tight fit.

But the IRM B4/B4 bogies have caused no such problem, I have done 6 coaches worth to date, the axle length on the insulated sleeve remains the same, as the wheels are moved out on the axles. Hopefully this is clear in the picture I uploaded.

 

Edited May 16 by Brendan8056

[Horsetan]

1 hour ago, DJ Dangerous said:

So with one of THESE, a cheap wheel puller, the IRM wheelsets are easy to re-gauge to 21mm?

Might do. Want to give it a go?

[murphaph]

I used a cheap version of the Fohrmann puller to do the Tara's etc. I think it was called a RC model gear puller or something like that. I haven't tried it on the coaching stock.

[Mol_PMB]

I had a look for my B4 bogies this afternoon but failed to find them! I'm sure I bought a set, and they are with some other IRM accessories I got at the same time. They must be in one of those safe places.

I'll have another look in the week - hopefully I'll get some inspiration about where I put them!

[DJ Dangerous]

On 16/5/2026 at 9:11 PM, Horsetan said:

Might do. Want to give it a go?

One day…

 

[Mol_PMB]

I have some information to report, as I void the warranty on the first of my Park Royals.

The wheelsets can be removed from the bogies fairly easily. 

The brake gear has some impossibly fragile bits near the ends of the bogies, and even casual handling of the bogie will leave your workbench littered with small black bits of plastic that were once part of the brake gear. 

The main brake gear mouldings aren't so fragile, but they're firmly attached to several parts of the bogie frame and I haven't yet succeeded in removing them without damage. They have to come out because the brake blocks foul the wheels set to 21mm gauge.

 

Now to the wheelsets. The wheels move moderately easily on the stub axles (much more easily than the IRM Bulleid wagon wheels). I used my press tool as shown:

Note that the brass bit in the middle is several bits of tube soldered inside each other, to provide a conical recess that goes on the end of the axle, and a flat-bottomed recess that slides over the press tool tip. So this enables me to push pinpoint axles without blunting them - it doesn't push on the tip itself.

I was able to achieve 19.2mm back to back with the wheels pulled right out to the end of the parallel part of the axle.

Note that none of this moves the axle halves in the muff, or indeed puts any force on that joint.

The axle halves are 2mm OD, so the wheels could be replaced with other standard wheels to a finer profile if required. But if you want to keep the lighting, you would need to reinstate an electrical connection between tyre and hub of a normal plastic-centred wheel.

Because I use EM track standards with 21mm gauge, I think I can get away with the IRM wheels pulled out to the right BTB.

 

Now, taking out the brake gear is frustrating because there's going to be a lot of work to put the broken bits back in (or replace them). This is the remnants of what I had left:

Having got that out, the wheels can then be put back in - a bit fiddly but not too bad:

But the flanges rub on the spigots which used to mount the inner brake hangers, so they need relieving. 

Once that's done, you have a free-running 21mm gauge bogie with no brake gear.

I'm going to try putting some of the brake gear back together tomorrow, probably replacing some parts with wire.

 

I'd be interested to see how anyone else gets on!

 

[lucas]

Interesting that they have 2mm axles unlike the Mark 2s. They might not be so difficult to regauge after all so.

Is there anything inside the sleeves preventing the axle ends from moving further in? One thing I worry about is that the axles will slowly work their way further into the sleeves over time, changing the BTB and overall axle length, but also running the risk of shorting out internally.

I'm still patiently awaiting my order, but looking forward to doing some experimentation when they arrive.

[Mol_PMB]

I haven’t done anything with the muffs, not tried to take them apart or put any force on them. 
I imagine there’s an insulating spacer in the middle, which would keep the axle halves apart. 

[DJ Dangerous]

4 hours ago, Mol_PMB said:

I have some information to report, as I void the warranty on the first of my Park Royals.

The wheelsets can be removed from the bogies fairly easily. 

The brake gear has some impossibly fragile bits near the ends of the bogies, and even casual handling of the bogie will leave your workbench littered with small black bits of plastic that were once part of the brake gear. 

The main brake gear mouldings aren't so fragile, but they're firmly attached to several parts of the bogie frame and I haven't yet succeeded in removing them without damage. They have to come out because the brake blocks foul the wheels set to 21mm gauge.

 

Now to the wheelsets. The wheels move moderately easily on the stub axles (much more easily than the IRM Bulleid wagon wheels). I used my press tool as shown:

Note that the brass bit in the middle is several bits of tube soldered inside each other, to provide a conical recess that goes on the end of the axle, and a flat-bottomed recess that slides over the press tool tip. So this enables me to push pinpoint axles without blunting them - it doesn't push on the tip itself.

I was able to achieve 19.2mm back to back with the wheels pulled right out to the end of the parallel part of the axle.

Note that none of this moves the axle halves in the muff, or indeed puts any force on that joint.

The axle halves are 2mm OD, so the wheels could be replaced with other standard wheels to a finer profile if required. But if you want to keep the lighting, you would need to reinstate an electrical connection between tyre and hub of a normal plastic-centred wheel.

Because I use EM track standards with 21mm gauge, I think I can get away with the IRM wheels pulled out to the right BTB.

 

Now, taking out the brake gear is frustrating because there's going to be a lot of work to put the broken bits back in (or replace them). This is the remnants of what I had left:

Having got that out, the wheels can then be put back in - a bit fiddly but not too bad:

But the flanges rub on the spigots which used to mount the inner brake hangers, so they need relieving. 

Once that's done, you have a free-running 21mm gauge bogie with no brake gear.

I'm going to try putting some of the brake gear back together tomorrow, probably replacing some parts with wire.

 

I'd be interested to see how anyone else gets on!

 

Excellent to hear that there is no need for new wheelsets!

[Mol_PMB]

I've got the bogies all back together and the paint touched up. It's not perfect but it will do.

First step with the brake gear was to drill a 0.25mm dia hole into the top of the inner brake hangers, and glue in some fine wire:

Then drill similar holes in the bogie frame spigots, and glue the brake hangers into their new place. 

The single moulding that makes up the rest of the brake gear (apart from whatever fell off when dismantling) then needs to be cut in half lengthwise. The two halves can then be glued onto the top of the bogie frame spigots, with the appropriate lateral spacing for the new gauge: 

From the underneath it looks like this:

Then I got some steel wire and cut it to lengths to fit between the brake blocks. Using superglue and spring clips I used this to re-connect and reinforce the brake cross-beams, first the inner ones:

And then the outer ones:

Finally I stuck back on any brake blocks which had been a casualty of the process.

A coat of matt black paint and this horrendous bodgery disappears into the shadows quite nicely!

 

Hopefully, now I know how to do it, I can break slightly fewer bits when I come to do a silver pair.

[Horsetan]

15 hours ago, DJ Dangerous said:

Excellent to hear that there is no need for new wheelsets!

There is if you work to P4 standards. AGW produce electrically-live 12mm disc wheels (which I had several of for the Mk2 bogies) so it is technically possible to swap the IRM wheels using the same stub axles without needing converter bushes. It will require suitable press tools, though.

[lucas]

First attempt at regauging hasn't gone so well...

Looks like the sleeve just keeps the axles insulated from each other using a friction fit on the axles. There is no internal spacer keeping the axles apart.

Even when set to 16.5mm there is a small gap between the sleeves and the back of the wheels, so moving the wheels out shouldn't make the axles any more likely to move within the sleeves. We just need to be careful not move the axles within the sleeves during the regauging process.

I will be trying to get some conductive EM wheels to replace the code 110 factory ones. Although EM track is very tolerant of coarser wheels they are pretty massive and unsightly in my opinion.

It's going to be pretty difficult to fit new wheels without removing the axles from the sleeves, so now I just need to find a reliable way of getting the axles out without the sleeves exploding on me.

[lucas]

I finally got around to properly regauging my Park Royals.

I used Alan Gibson conductive EM wheels since I personally don't like the look of NMRA code 110 wheels, and the process should be the same if you're using P4 wheels. Anyone who wants to regauge the factory wheels can follow Mol's post above as a guide instead.

 

To start disassembly of the factory wheelset I gently pulled the two halves apart with my hands. This is enough to pull one of the two half-axles out of the insulating sleeve.

To pull the other half axle out it is actually a bit more difficult. DO NOT just grab the sleeve with your pliers and pull, see my previous post for the consequences.

First I pulled out the wheel a bit to create a gap between the back of the wheel and the sleeve. The throat of my puller is not wide enough to fit the sleeve, but I've come across this problem before so I have a short length of aluminium tube that I use for this purpose.

Once there is a bit of a gap I put that in my puller and used a small length of 1.5mm diameter rod to push the remaining half axle through the sleeve.

  

Once the two half are out of the sleeve they can simply be pressed out through the wheel to get a completely disassembled wheelset.

 

I pressed two nice shiny AGW wheels onto the half axles. These are not quite as tight a fit as the factory wheels, so take care when pressing that the wheels go onto the axles straight.

I pressed them in a little further than necessary; it is very easy to pull them back out once the wheelset is reassembled, but nearly impossible to press them further in. (Apologies about the out-of-focus photo for this one.)

Then I gently pushed the two half-axles back into the insulating sleeve bit by bit, measuring the total length of the axle as I went. I made sure the sleeve was approximately centred so both half-axles are firmly held in position. The overall axle should be 28 mm; 2x 13.5 mm half-axles with a 1 mm air gap inside the sleeve.

Once the axle length was correctly set, I pulled out the two wheels to the correct back-to-back, 19.3 mm for EM in my case.

Take care not to put any pressure on the pinpoint as you could easily mess up your axle this way. I use a 1 mm inner diameter brass bushing which I have given a suitable chamfer on the inside. 

To replace the sleeve I broke I cut a small length of polystyrene tube. This is nominally 1/8" outer diameter with unspecified inner diameter, but snugly fits the half-axles.

This doesn't grip the axles as well as the proper sleeves, so I cut it to the same length as the back-to-back to prevent the axles from creeping in any further. The slightly sprung bearings on the bogie should prevent the axles from moving any further outward, so this should be sufficient.

I am nothing if not consistent at being 0.01 mm over on all my measurements  

 

Before installing the freshly regauged wheelsets, I modified the brakes as these foul on the flanges of the 'correct' gauge wheels.

First step was to snip the linkage from the outside brake shoes. In my Park Royals the linkages are not sufficiently glued to the inside brake shoes, so they can be gently pulled apart.

Once it is loose the linkage piece can be 'unhooked' from the frame on both ends, gently manoeuvred back and forth, and eventually lifted out from the top side of the bogie.

 

Then I gently snipped off the 8 brake shoes. For the outside ones I tried to cut the brakes along with the pivots to keep them as one piece. This worked for some but not for others; for some the glue bonding them together was not enough to prevent the tiny pivot piece from flying away.

To prevent the regauged wheelset fouling the inner brake mounting pieces I had to file a small chamfer on the outside edges which you might be able to make out in the photo below. This is definitely necessary if you're using RTR or EM wheels, but you might be able to skip this if you're using P4 wheels.

Then the final step is to install the wheelsets and carefully glue the brakes back in place. Mol's technique of using fine wire above is probably stronger, but I was lazy so I just used Superglue and glued the brakes into position.

I haven't tried bisecting the linkage and gluing it to the brakes yet, it's something that won't be visible unless you have one heck of a derailment anyway, but I will probably end up doing that similar to what Mol showed above.

And here is the end result installed under the coach: