What is the difference between a Class 121 and Class 122 'Bubble Car'?

I’ll leave you to ponder that little question for a while. However, as you may have seen in the last blog the railway has taken steps to hire in a new DMU for the early part of the season, after the sale of the Class 117 set. This is where the question above becomes relevant!

The DMU in question is Class 121 ‘Bubble Car’, W55024, which has been hired in from the Chinnor and Princes Risborough Railway. The ‘Bubble Car’ arrived at Toddington on the 25 Feb, with its FTR Exam conducted the following day. The following weekend it was pressed into service on our BLUE Timetable. 

On hire Class 121, W55024 arrives at Toddington from the Chinnor and Princes Risborough Railway. (Kev Jarvis)

 

As with both classes of ‘Bubble Car’, the Class 121 DMUs were built for use on branch line services where capacity was pretty low. The Class 121s were built expressly for use on Western Region lines and were very common in Cornwall, the Bristol area and, eventually, in the London area – from where the last remaining units (including 024) worked from Aylesbury depot. The Class 122s were originally built for use on the LM region, but eventually found their sphere of service expanding to include the Western and Scottish regions. Some Class 122s were even converted for parcel traffic and redesignated as Class 131s.

Although built by different companies – Class 121 by Pressed Steel Ltd and Class 122 by Gloucester RC&W – both classes were almost identical; hence the question above! Have you worked it out yet (and no looking at Wikipedia!)?

Many of the vehicles of both classes, including 024 ended their mainline service in use with the Departmental sector, although a small fleet were reactivated for passenger work by Chiltern on the Aylesbury – Princes Risborough shuttle services…. hence why a number of vehicles are now preserved on the CPRR. Many ended up as route learners however, two ended up in use as Severn Tunnel evacuation units.

Okay, I’ve left you hanging far enough. So, what is the difference???  

Our very own Class 122, W55003 at Winchcombe while undergoing asbestos removal. Notice the different cab front to the Class 121 above.

 

Well, as you can see from the photos above, Class 121s were built with a 4-character route indicator box above the cab windows. Class 122s, like our own W55003 had destination blinds built in the same place instead. There was one exception to that rule, however, as W55033 (a Class 121) was built with a destination blind instead of the 4-character route indicator box. Why is a bit of a mystery! The Class 121 was also the longest serving 1^st-generation DMU, clocking up an impressive 57 years in mainline service. A duration probably only matched/bettered by the venerable Class 08, some of which are well into their 60s in mainline operation!

A nocturnal shot of W55024 at London Paddington in 1979, along with one of the unpowered Driving Trailers that were also built as part of the class to strengthen capacity. This is something that we hope to replicate with W55003 and W51360 in the future. This photo is courtesy of Martin Hilbert (Flickr)

In comparison to the photo above, here 55003 is seen at Leamington Spa in January 1987. (Courtesy of Jamerail on Flickr)

So, W55024 will be with us for a short period to cover the off-peak timetable while our own W55003 continues its route through overhaul. Traveling on a ‘Bubble Car’ is an experience as their suspension gives a very unique and bouncy ride compared to a 2 or 3 car DMU. They are also surprisingly quick to accelerate as they only weigh a little over 38 tonnes – roughly the same as a standard Mk. 1 coach! Why not head on down to see for yourself!

(Courtesy of GWSR DMU Facebook)

On the subject of W55003, the overhaul progresses and has reached a bit of a milestone in the last couple of weekends. With the flooring pretty much completed, the first batch of seating frames were anchored in place - see above. A job that was completed last weekend with all the frames in and anchored to the floor. The external hand rails were also added to the Guard’s entrance.

New grab rails fitted to the Guards entrance on W55003. (Courtesy of GWSR DMU Facebook)

 

An agreement has also, apparently, been reached between the Motive Power, C&W departments and the railway to ensure the upkeep of the DMU vehicles left on the railway. As far as the Diesel Department goes, we will be responsible for the mechanical side of things such as the engine and traction systems.

It is hoped that W55003 will be back in action in time to complete the BLUE timetable days at the end of the running season. It would also be good if it was ready in time to do a few runs with W55024 before it heads back home.

Elsewhere, the remaining Class 117 DMS on the railway, W51360 has had its exams completed and is fit for traffic, should passenger numbers require strengthening of the DMU numbers on the BLUE timetable. However, with W55024 in a non-standard BR Maroon livery and W51360 in all over BR Green, the colour clash would be pretty horrific!

Continuing with our new visitor, 024 received fitters attention from the Wednesday Gang on 12 March after it had developed a fault with one of its cab gauges. A suitable and calibrated replacement was found, fitted and tested whilst the unit (along with W55003 and W51360) also underwent air pressure testing for our railway insurers. 

W55024 sits on Road 11 at Toddington MPD. In the cab, Paul C and Hugh J have just driven it over from Road 2 - the DMU siding - so that the 'bubble car' can have the errant gauge removed and replaced and, the air tanks could be pressure tested.

 

The overhaul of Class 26, 26043 has also reached a new target with the loco now in suitable condition to break cover from the David Page shed and be stored outside for a short period. The bodywork on the ‘McRat’ is pretty much complete and it now wears the first layer of blue undercoat, along with yellow undercoat on both cab fronts. Some areas have also received the first application of top coat gloss.

On 22 Feb, 26043 broke cover and ventured into the open for the first time in a long while. Space was required in the David Page shed for the arrival of 'Betton Grange' and so D2280 was fired up to move the Class 26 onto Road 10 for work to continue.

The cab windows have been refitted and the new cab doors, that were manufactured by our colleagues in C&W, have been painted in undercoat and fitted to the loco – replacing the previous ill-fitting doors. One of the doors proved problematic to fit due to historic collision damage, but this was only a minor inconvenience.

In the sunshine, the colours of the undercoat (and some areas of top coat) shine through and show the incredible progress on 26043. Still plenty to do but the finish line is now within reach.

 

The cab interiors are coming together with cab desk surrounds being repainted and refitted, new flooring being fitted and the interior paintwork being refreshed throughout. The cab seats are also currently being refurbished with a view to being refitted in the cabs shortly. Elsewhere, the underframe and bogies are receiving top or undercoat where required, as are the engine room walls after a spot of sanding down.

The cab interiors are slowly being refitted and the pipework repainted. New flooring has also been fitted.

The engine overhaul of Class 24, 5081 continues along with the refreshing of the cab interiors. With the pistons, liners and rings removed for assessment other parts of the engine have been removed for a bit of TLC – something the engine room probably hasn’t had in a couple of decades at least! The last time the loco had an overhaul was in 1975! The cab walls are receiving new corkboard to replace previous board that probably had also been there for some time.     

With the introduction of the mainline diesel fleet to timetabled workings rapidly approaching, the serviceable fleet have been receiving their yearly B Exams. Usually conducted by BR at more regular intervals than in preservation, these examinations ensure that the safety critical and non-safety critical, but still important, elements of the locomotive are in a safe and fully operable condition.

For instance, with a Class 37, a B Exam would be undertaken every 250-275 engine hours. The tasks conducted during this exam would vary from the basic – cleaning the cab windows – to the seriously safety critical, such as wheel flange tolerance and DSD operation.

Although the number of engine hours differed from class to class, the contents of the B Exam would be fairly universal and would be geared towards the loco maintaining a safe operational condition. Locos in preservation do not build up the same number of hours as quickly as they would have in BR service – if you added up the engine hours in a year from any individual loco of the fleet over the course of a running season, it would probably come very close to the guidelines used by BR, whereas in BR traffic a B Exam may have been conducted bi-monthly depending on use. Not least of all, our locos do not spend huge amounts of time idling so don’t rack up engine hours whilst stationary and, the physical demands on the loco are much lower. 

D6948 has been the first loco to have its B Exam completed as it will be the first loco rostered in April - undertaking a Driver Experience on 4 April followed by the PURPLE day on the 5 April. 

Part of the B Exam is looking at the levels and consistency of the fluids. Here, I am checking the Radiator Fan Oil to ensure the reservoir is full and that the oil is looking clean and free of debris.

 

D6948's B Exam went without issue and, after I had completed most of the non-critical tasks a couple of weeks before, the safety critical elements were all examined and signed off on the 26 Feb. Sister loco, 37215 will be starting later , so the B Exam isn't as pressing. The Growler Group are aware of a few growing issues with '215' that will require an extended period out of service in the future, but for now she should be declared fit for service in the next couple of weeks. 

Elsewhere, the B Exams on the Class 47s should also be completed shortly with the first Class 47 allocation being 47105 on the PINK TT day on Sun 6 April. As with the Class 37s, the '47s' haven't had much to correct in the way of maintenance issues and this has allowed the chaps from the BT4F to concentrate matters on 5081's engine and cab overhaul. 

5081 sits in a sunny Toddington shed during its engine overhaul. Several of the BT4F are members of the small group that own the loco so, with both Class 47s requiring little attention over the winter, full attention has been given to the Type 2. 

 

Class 20, 20228, continues to be readied for eventual solo service in 2025. The pipework reinstating the exhauster is being prepped and fitted with the exhauster itself pretty much ready for siting and then eventual testing. 

An array of cylinders and pipework ready for reinstalling the exhauster into 20228. Sadly, they won't stay that clean for long when fitted!

Sister loco, 20137 continues to reside in the yard while 20228 continues to be worked upon. For winter '137' had its AVR removed to prevent frost and water damage and this will need to be refitted, tested and a B Exam completed before it is fit for traffic. It's first venture will be on the PURPLE TT on Thurs 24 April.

Locked out of traffic and awaiting reinstating, 20137 sits down by the old Diesel Department pit and A Frame hoist.

With the majority of CMDG attention being on the Class 26, the 'Peak' 45149 has still received some minor attention over the winter to ensure it is fit for traffic. As with others in the fleet, it is awaiting its B Exam before taking its first rostered turn on the PURPLE TT on Saturday 19 April. 

One piece of work for the 'Peak' that I have been involved in (its been a while!) was on Wednesday 12th March when myself, Andy and Hugh were tasked with fabricating a new exhaust cover for '149'. The old one had blown off the roof at some point and had then been damaged somehow. So the three of us set about testing our woodworking skills!

The exhaust port of 45149. It is usually covered to prevent too much water getting into the engine, however the previous model of cover had become critically damaged after being blown off.

 

After measuring the port, it was time to go and scavenge some wood and material to make a new cover. Hugh put the idea forward of having a longer section on the underside that would fit quite snuggly into the port and therefore make it harder for the wind to get underneath it and blow it off the roof. After finding sufficient quality of plywood, a frame was made to sit in the port reducing the chances of it lifting. 

After some accurate sawing from Hugh, and the sides all screwed together. This section will sit in the port quite tightly and therefore reduce chances of the wind getting underneath it and lifting it out of the port.

 

Andy looks on as Hugh expertly saws some spare would to provide support to the frame.

 

With the frame completed attention turned to the lid. Hugh managed to find some scrap floor trip with which to fashion a crude, but effective handle, to make it easier to lift the plug out. The lid was cut from a large piece of 6mm ply that had been lying around for ages. Andy had found some scrap floor vinyl that would just about fit around the lid. After some heating and stretching of the vinyl, we were able to screw it down to the lid to give it some protection from the elements. 

Crude, but functional! The finished article.

Although it isn't something that would find a place in the Louvre, the cover fit quite nicely and should do the trick pretty effectively. 

The week just passed (10 - 14 March) has seen the railway operate the usual Race Trains on behalf of a private operator that hires the use of the rolling stock. These are, as requested, steam hauled which gives us in the Diesel Department a little extra time to get our locos in A1 condition. However, back in the 1960s and 1970s diesel traction would be utilised to bring racegoers to Prestbury Park by way of special services to Cheltenham Race Course station. 

On his Facebook page, 'The Stratford-upon-Avon to Cheltenham railway archive', long time volunteer Tom Cullimore has posted a number of photos from that period showcasing the different traction used on these 'Race Specials'. It is quite surprising what used to turn up on the special trains! Here are some examples courtesy of Tom, and used with express permission. The photographer, if known, is given in the caption. If you want to see more, head to the page (you have to have a Facebook profile) -  https://www.facebook.com/groups/1293863581633273

Firstly, we start with a photo that a lot of people on the railway would love to recreate if we could get one to visit...

Maroon liveried D1012 'Western Firebrand' departs from Cheltenham Race Course station with an ECS service for Toddington Yard. The 'Western' had worked 1Z41 from London Paddington. Toddington Yard was retained to stable the stock of Race trains rather than have them run to Gloucester or Worcester. (The late Bill Potter)

 

A scene that could have been from only a few years ago but is from 17 March 1972. Class 47, 1743 (later 47150) arrives at Racecourse station with 1Z22 from Blackpool. In Platform 2, 'Peak' D138 (later 46001) waits to run ECS to Toddington. The '47' would run its stock ECS to Gloucester. (John Medley)

'Hymek' D7052 in BR Blue hurries through Pittville, at what is now the limit of the track bed owned by the GWSR, on its way to Racecourse with a train full of race-goers on 20 March 1968. (The late Bill Potter)

 Saving a rarity for last, and another one form the lens of the late, great Bill Potter .....

 

Class 40s were pretty rare on the Honeybourne - Cheltenham line but, on 14 March 1967, D331 (later 40131 under TOPS) heads away from Racecourse station and towards Bishops Cleeve with a special returning punters to Wolverhampton.

Get yourself over to the site, if you haven't done so and have enjoyed the four photos above - or if you have any photos of the line prior to 1976 (steam and diesel) that you wish to share with the wider community. 

Also, for those of you interested in Railwayana and collectables, here is an event that may interest you taking place in Crewe in June. Although we aren't there this year, the Growler Group will have a table in 2026.

 

So, finally, the loco roster for the end of March and into April. Where a loco class is shown with 'xxx', the rostered loco is yet to be decided or is not known.

Date	TT	Rostered Loco(s)
Sun 16 Mar		W55024
Sat 22 Mar		W55024
Sun 23 Mar		W55024
Sat 29 Mar		W55024
Sun 30 Mar		W55024
Tues 1 April		W55024
Wed 2 April		W55024
Thurs 4 April		W55024
Sat 5 April		D6948
Sun 6 April		47105
Tues 8 April		W55024
Wed 9 April		W55024
Thurs 10 April		W55024
Sat 12 April		47xxx
Sun 13 April		D6948
Tues 15 April		47xxx
Weds 16 April		47xxx
Fri 18 April		47xxx
Sat 19 April		45149
Sun 20 April		45149
Mon 21 April		47xxx
Wed 23 April		D6948
Thurs 24 April		20137
Sat 26 April		45149
Sun 27 April		45149
Tues 29 April		W55024
Wed 30 April		W55024
Thurs 1 May		W55024

Once resident at Toddington, now based at Midsomer Norton on the S & D, Class 08 D4095 (08881 under TOPS) rests in the sun at Carriage and Wagon, Winchcombe back in the mid-2000s. (Richard Drewitt)