Dapol 7mm scale B4 loco

V

victorianman

Western Thunderer
Hello. just wondered if anyone has converted one of these to S7. Apart from being a smidgen over-wide and flanges (approx. .7mm thick) being fine but still a little deep for the standards, the wheels are within a gnat's of being S7. The initial thought is to pull the wheels out on the axles, though I am aware wheels can revolve out of quartering as this is done. The axles (4mm dia.) are also just a little short of being flush with wheel boss on my example, and the wheels are mounted on insulating bushes. Behind crosshead clearance doesn't seem too bad, but as on the 4mm version, the crosshead is able to slop around quite a bit.
Any thoughts gratefully received.
 
Andrew

Andrew

Active Member
victorianman said:
Hello. just wondered if anyone has converted one of these to S7. Apart from being a smidgen over-wide and flanges (approx. .7mm thick) being fine but still a little deep for the standards, the wheels are within a gnat's of being S7. The initial thought is to pull the wheels out on the axles, though I am aware wheels can revolve out of quartering as this is done. The axles (4mm dia.) are also just a little short of being flush with wheel boss on my example, and the wheels are mounted on insulating bushes. Behind crosshead clearance doesn't seem too bad, but as on the 4mm version, the crosshead is able to slop around quite a bit.
Any thoughts gratefully received.
Click to expand...

Hi Goeff

I converted a Dapol B4 to S7 for my brother's dockside layout just over a year ago. It was 'relatively' straightforward but really tested the little grey cells. Each stage was tricky but I can share a few pointers for you to consider before getting underway. Bear in mind that the model I worked on was produced in 2023 and I am not sure if there have been any updates/modifications to the later batches which may need to be factored in. I was very impressed with Dapol's rendition, dimensionally accurate and certainly looks the part.

As you have observed, the wheels are close to S7 standards. The axles were 34.5mm o'all with a 3.5mm spline at each end. This unusual feature turned out to be useful in achieving accurate quartering and grip when refitting wheels. If I remember correctly, I decided to take a skim off the front face of each tyre to reduce the width to 3.4mm, reprofiled the flanges with the S7 tool and also filed down the crank pin bosses so that the coupling rods just cleared the face of the wheel ( on my model I achieved finished width of 43.20mm boss face to boss face). This work was essential in reducing the overall width when the rods are then refitted. This is particularily important at the front end as you will no doubt have observed, the front axle rocks, which helps with stability/electrical contact but adds to clearance issues! On my conversion the internal distance between front steps was 53.30mm. The slop in the crosshead arrangement must be reduced to avoid contact at the back of the steps and the way I did this was to 'sleeve' the hole in the cylinder stuffing box with a short length of fine bore brass tube of suitable internal diameter to accommodate the piston rod. This will also entail enlarging the hole in the stuffing box to accept the external diameter of whichever tube you select - but be careful, the stuffing box is not very deep and can easily be damaged. I did this 'very gently' with the drill of appropriate size in a pin vice. The last bit is to secure the tube with a drop of superglue, again with great care. This entire operation is carried out with the cylinder units detached from the chassis. Whilst you still end up with minimal clearance, it is clearance nonetheless and my conversion worked without issue. You will also note that the loco has plunger pick-ups which are helpful in centralising the wheelsets. One last point; remember to fit slim washers before re-assembling the wheelsets to further reduce slop. I made my own and I think I settled on a thickness of 1.5mm.

Most of the above is from my sketchy notes taken at the time and a little from memory ( such as it is these days). If I think of anything else that may be of assistance, I will add detail as and when.

Good luck.

Kind regards,

Andrew
 
V

victorianman

Western Thunderer
Andrew, Richard, Spikeyfaz, thank you all so much for your comments re my query. Several things raised that I must think about, particularly the shimming to stop crosshead slop. I have successfully built and exhibited a Slaters F Manning Wardle in S7, so the tight clearances are familiar. That loco, of course, helpfully has twin slide bars, so clearance work can be concentrated on the front crankpin.
Very grateful that you all took the time to make suggestions.
Many thanks.
 
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