One of the many projects that I have been contemplating is a Keykits 7mm scale Kerr Stuart 6wd No 4415. The kit was the last one produced by Kay Butler, after she had sold the Wrightlines range to ABS Models. It is for the prototype Kerr Stuart 6w diesel 4415 with body masters by Keith Millard and milled brass chassis components by Kay. I have had it for some years (from new) and I am finally getting round to it. My version may well be that of its unknown sister happily chugging away on an unknown line in Shropshire! The kit comes with enclosed panels inside the cab, hiding where the diesel engine would have been. I think this was what was fitted to the production versions of these locos in an attempt to reduce the noise in the cab. However, it was the picture on the KS restoration project web site that made me think the prototype version only had a mesh cage around it.
The cab front had two large cut-outs which at first sight looked like they may have been covered in mesh but closer inspection of a better quality picture suggested to me that it was actually the mesh around the engine that could be seen through the cut-out.
Then Allan C Baker published a very useful book. Which has helped me work out what the diesel engine looked like. The restoration project Facebook and Instagram pages have also proved to be extremely helpful with lots of photos of the cylinder block and heads.
I started cobbling together details and wondered if it was worth investing in 3d CAD and printing when I realised that all you were likely to see was the outline, so a detailed model would be a bit pointless. Out came the scrap box of plastic sheet off-cuts and after a bit of crude hacking I have ended up with this.
The image in the book has been tweaked to remove the air inlet manifold which I have (obviously) had to include in my mock up. I only needed to represent 3 of the 4 cylinders as the motor in the kit gets in the way of the fourth cylinder.
I have no details of the fan so I just cut a disc from brass sheet and shaped it to give a representation. It probably won’t be seen so I am not too worried.
A test fit on the chassis confirmed that it was about right but I thought I should do a better check with the engine supports and radiator.
It’s a bit far forward and needs to be moved back into the cab but I think it is going to be okay. Unfortunately the controls provided in the kit, whilst based on the best available information at the time, are not close enough for my use and I had to fabricate something more suitable based on the information from the book.
Looking a lot better after a coat of paint!
A bit of a mixed day with some progress and some frustration! I am finding that the mild arthritis in my fingers is making it much harder to work and shape small parts.
I made good progress with the gear change levers and clutch pedal.
I cut some NS sheet to form a spacer plate to which I could solder the two frame uprights. These have had the engine covers cut off them and the cab front has had a hole cut in it. It has been a grey day here so I am afraid that the photos are not very good.
The radiator fits at the back of the frames. It is a solid lump of white metal so I needed a blob of blue tack to stop it from falling over. I have re-positioned the JAP starting engine to move it further back and higher up so that it lines up better with the engine (or at least it will when the engine is fitted).
The original motor was a cheap Mabuchi one with a gear drive to a lay shaft. I have replaced it with a motor, 3d printed casing and flywheel from Tramfabriek and a pulley set from Locos n stuff.
I am pleased with the way it has worked out and it is a heck of lot quieter. At the moment I have just a single pulley and belt drive but I have the option to add a second set if it needs it. The chassis is very easy to dis-assemble so it is easy to get to the lay-shaft and motor and just add another set of pulleys. Time will tell, the body is quite heavy but the test will really only be at an exhibition (remember them?) as I can’t really do much at home – especially as I want the garage for the new layout!
I have struggled so much with the gear change levers. I wasn’t happy with my first effort so I have redone them and got something that I am happier with. Still not as good as I would have liked but it is the best that I can do. It is all a bit fatter than I would have preferred so the linkages have to be bent to fit through the cab front. The opening of the cab front is smaller than on the prototype due to the thickness of the side panels and locating rib. That’s going to be an acceptable compromise as far as I am concerned!
Hopefully it will all look better when hidden under paint and behind the driver. The radiator makes it a bit back heavy despite the blue tack support and it won’t slope back when finally fitted (I hope). A trial fit with the engine confirms that everything looks okay.
I have decided not to fit the fine mesh that I have for the engine guards as it hides all the detail! I can see now why it is so much easier to build the kit with the solid engine cover panels! Still, why make life difficult when, with a bit more effort, you can make it impossible.
This was the look that I was after, where you can just about see the engine and controls through the square cut out in the cab front.
I was trying to simulate this photo from the KS restoration web page:
But obviously mine is in a much later condition.
It is quite gloomy inside the cab behind the radiator so my lack of detail doesn’t really show up (as expected). I am pleased that you can at least see the levers and I think I will leave the mesh guards off as they would hide anything that can just about be made out. Even less will be visible when the driver is added too.
Putting the finishing touches on the Kerr Stuart caused me to stop and think about how they would fill the fuel tank. This was inside the body at the front of the horizontal part of the body. Looking at the cross-section drawings I think there was a flap in the front left hand corner of the large removable cover on the top of the body. It is a bit late for me to model that but I might try to add something later. Looking at the geometry of the air inlet and exhaust manifolds for the engine makes me think that the original two ‘pots’ on that top cover were an air inlet (LHS) and exhaust (RHS). It looks like the later locos had the air inlet filter inside the bonnet and I think that is were No 4415’s was moved to when they fitted a better silencer to the exhaust. It also looks like the production locos had this exhaust silencer mounted centrally on the top plate while it was off-set to the right on the prototype, presumably to line up with the existing exhaust manifold. Even with the modifications I guess it would have been quite noisy inside the cab. Right and left are when looking forwards from the cab.
Testing the finished model confirmed that even a double belt drive was not enough to move the Kerr Stuart so I have gone back to the original gears. Although they are plastic they are still noisier than the belt drive. Looking on the bright side, I don’t need a sound chip!