Dapol Class 122 conversion to S7 and adding DCC

Discussion in 'S7 Group' started by richard carr, 26 August 2021.

  1. richard carr

    richard carr Western Thunderer

    My Dapol Class 122 DMU arrived yesterday after spending several months stuck in a container in the Suez canal. Thankfully they all survived intact.

    It looks really good if you ask me,


    It comes screwed to a picec of perspex

    There is plenty of interior detail



    Once you have unscrewed it from the Perspex there are 2 battery boxes that need pushing firmly into place


    There is a bag of detail bits to go on the front vac pipes air pipes and speedo.

    Then the hard bit converting it to S7

    Both bogies are powered and once you take the retaining plate which is fixed to the side frames you see this.


    so it is going to require very careful removal and replacement of the reprofiled wheels on the axle, I won't be thinning the wheels as there won't be enough axle to push home given they are fairly thin in the first place.
    It might be a case that new wheels are needed but hopefully not.

    BrushType4, 3 LINK, fenman and 11 others like this.
  2. eastsidepilot

    eastsidepilot Western Thunderer

    Surely Richard it wont make any difference to the amount of axle the wheel is pressed onto whether you reduce the wheel width or not because the b-t-b measurement is fixed at 31.25 regardless so take the wheel width reduction of the front face, if that makes sense. If you leave the wheels at F/S tyre width it might bind on the inside of the bogie frames ?

  3. PaxtonP4

    PaxtonP4 Active Member

    What is the Dapol wheel tyre width? My experience of Dapol wheels is that they are very nearly scale width as they are.

    Also the flange depth is near enough to live with as well.

  4. NewportRod

    NewportRod Western Thunderer

    I just happen to have a Dapol wagon and a vernier by my side so here goes:

    Tyre width is 3.5 mm, i.e. 6" equivalent compared with 2.9 mm (5"equivalent) for wagons and coaches

    Flange depth is 0.88 mm (1.5") compared with 0.68 mm (1.125") (data from Website of the ScaleSeven Group).

    I've had success before pushing Minerva wheels out to S7 back-to-back so I'll try the same with this Dapol set.

    daifly likes this.
  5. richard carr

    richard carr Western Thunderer


    I'm not planning to thin the wheels, they measure 3.5mm thick so only half a mm over scale, 2.5mm should be enough to get a good seating on the axle.

  6. eastsidepilot

    eastsidepilot Western Thunderer

    S7 standards for loco/diesel wheels are 3.16 min to 3.25 max so as you say if you leave them as they are you'd only be 0.25mm oversize. But what is more important is flange thickness.

  7. richard carr

    richard carr Western Thunderer


    I will be reprofiling the flange, thats the easy bit.

    Was that my Western you had at Love Lane, it certainly looked like it !

  8. eastsidepilot

    eastsidepilot Western Thunderer

    I didn't know who's loco it was. John asked me to test run it and then take it back. I don't doubt he'll be delivering them soon.

  9. richard carr

    richard carr Western Thunderer

    I hope so Col, they have been in the UK for nearly 2 months now !
    Mine is green with small panels so it could be that one, I can't remember what number it is though.
  10. richard carr

    richard carr Western Thunderer

    The calss 122 is now converted to S7 and it isn't too difficult.
    This is how I did it.

    First remove the 6 screws holding the bogie frames in place



    The wheels and axles will then just lift out.

    Next use a wheel puller to remove the wheels from the axle, I wouldn't try pulling them off as you will probably damage the plastic insulation.



    4 wheels off their axles, these are then reprofiled in the lathe, I use a couple of cast iron clamps to hold them and a HSS profiling tool you can buy from the S7 group.

    Then you need to put the wheels very carefully back onto the axles, I think the best way is to gently push them fully back onto the axle then I used the wheel puller to move the wheels 1mm further apart at each end, checking the back to back with some digital callipers.


    You then need to remove the brake support linkage you can see it this photo and then in the one below I have cut them out with some pliers.


    This now gives plenty of space for the widened wheel sets.

    I used some tweezers to help place the wheel sets back in the bogies, and the refitted the bogie frames


    I tested it on my rolling road and it runs very nicely, now I just need to fit a decoder.


    Attached Files:

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  11. simond

    simond Western Thunderer


    hypothetical question as I don’t model in S7 and the railcar is out of my era, but didn’t it need some kind of shims/washers/spacers to stop the axles (and the gears) moving out of alignment?

  12. richard carr

    richard carr Western Thunderer


    There is a small chance that the wheels might move on the axles but I doubt it will happen, my class 15 locos use the same axles and they haven't moved at all and have had a reasonable amount of use with decent sized train over the past 3 or 4 years. There is very limited side play in the finescale version and even less once you widen the wheel sets so the gears shouldn't move out of alignment.

    3 LINK and simond like this.
  13. Ressaldar

    Ressaldar Western Thunderer

    Hi Richard,

    would be interested in knowing what decoder and speaker/s you are proposing to use. I might see myself with a 121 in the near future, somehow, the 122 didn't quite have the same appeal - until the sandite/route learner era. It will be interesting to see what differences Dapol include on the Loadhaul 122 when they bring it out.


  14. richard carr

    richard carr Western Thunderer


    Of course, I've dropped an e mail to Youchoos to see what they have, the dapol instructions say it should be an 8 function decoder, so it will be interesting to see what Youchoos comes up with.

  15. eastsidepilot

    eastsidepilot Western Thunderer

    I can confirm it wasn't your loco, same livery though :).

  16. Muddysblues

    Muddysblues Western Thunderer

    Hello @Ressaldar Mike, I have on order from Digitrains, 2 x Zimo MX644c sound chips, and SP1 speakers, of which Dapol do recommend in the instruction booklet.

    Once I have received them, and fitted them I’ll give some feedback, but from what I have read, it seems to be a doddle to fit.

    Best regards
  17. Ressaldar

    Ressaldar Western Thunderer

    Hi Craig,

    nice to hear from you, I look forward to your report in due course.

    Stay safe and well


    Muddysblues likes this.
  18. Yorkshire Dave

    Yorkshire Dave Western Thunderer

    Interesting. Is there space to install another manufacturers 21 pin sound decoder rather than Zimo as recommended by Dapol since this rather forces ones hand and limits decoder choice. I seem to recall their 08 originally took a Zimo decoder and it was originally tricky to plug in an ESU decoder.

    (ESU are my preferred decoder as I have a Lokprogrammer!) :)
  19. richard carr

    richard carr Western Thunderer

    I purchased a Zimo MX644C from YouChoos earlier this week and fitted a single tangbang speaker in the guards van it meausres 66 x 29 x12 mm once you cut the fixing lugs off. I stuck it down with black tack. It all works as per youchoos instructions.
    I have also added the front end detail provided with the DMU (air and vac brakes speedo etc) and put some transfers on it for the head code and route indicator, as mine will be in the north east it is clearly a "special"


  20. richard carr

    richard carr Western Thunderer

    This is a much better picture, with lights on.