The Bachmann 'Gronk' seems to perplex quite a few people, firstly because it's not obvious how the body comes off and secondly when trying to find space to fit the decoder. It's actually extremely easy once you've worked it out. The loco isn't DCC-Ready which means the decoder needs to be hard-wired in. You'll also need to remove two metal protrusions using a hacksaw or cutters, but generally the conversion is a doddle.
Photo 1
All you need. The loco, a couple of screwdrivers, a decoder (in this case the Lenz LE1025A) and the double-sided sticky pad supplied with it. Also you'll need your soldering outfit and a craft knife or wire stripper - not pictured because they're not very photogenic! If your loco is a new one then it's probably a good idea to test-run it before proceeding in order to check everything is OK.
Photo 2
If you've not dismantled one of these before then you'll be wondering how it's done. Turn the thing over and you'll see a variety of screws on the underside. Resist the temptation to give any of them a turn - these are not the screws you're looking for.
Photo 3
The body is secured by two screws cunningly concealed under the couplings. Poke a small screwdriver under these (they're actually the rather useful NEM 362 sockets) and lever them out.
Photo 4
Underneath you'll find the screws you're after (circled in red in the photo) - undo these with a small cross-head screwdriver and put them to one side.
Photo 5
Remove the body carefully, starting at the back. Next to the screw you've just removed is a small tab in a hole that if pushed with a small screwdriver will free the rear of the body. Easing the body away from the chassis at this end will show that easy removal at the front is hampered by a length of bent wire. This represents the lighting conduit so lever it gently out of the retaining hole at the top of the steps using the ever-useful small screwdriver as in the photo.
Photo 6
There you have it - one of the sweetest running RTR mechanisms the UK modeller can currently buy. The decoder needs to fit where Bachmann's circuit board is screwed to the front of the chassis. There's plenty of space once this is out of the way, but not quite enough for my favourite Lenz LE1024A as it's too long. The shorter, double-sided equivalent (LE1025A) however, will fit here with room to spare.
Photo 7
Unscrew the two screws holding the circuit board in place and unsolder the four wires where they join the chassis and the motor. The circuit board can go in the bin!
Photo 8
Next you need to saw off the two metal pillars the circuit board was screwed into. This is quick and easy with a hacksaw but don't get carried away. You don't want to get bits of metal in the mechanism and you certainly don't want to snap the footsteps as I've done on two locos so far. Another technique that I've used on these locos is to snip off the pillars with an old Xuron track-cutter or similar device - this is probably safer for the loco but make sure you wear eye-protection as those two little pieces of metal aren't safer for you when they fly across the room.
Photo 9
Stick the decoder vertically at the front of the chassis using the supplied double-sided sticky pad, making sure none of the metal components can short out against anything. As I'll never fit lighting to this loco I've completely removed the unwanted wires from the decoder leaving just the red, black, grey and orange connections for the actual power. Cut back the black wire until it's the right length to reach the pickup strip on the left hand side of the loco and solder it in place. Solder the orange wire to the left hand side of the motor as in the photograph.
Photo 10
On the other (right hand) side of the loco solder the red wire to the pickup strip and the grey wire to the motor terminal in a similar fashion. Connecting the wires as described will ensure that the loco will move in the correct direction when you give the appropriate command. There's just enough clearance between the body and the chassis for the wiring as shown, but it's probably better to copy the route over the top taken by Bachmann in photo 6. I was copying another Class 08 - it seems no two are the same.
While we're on the subject of no two being the same, note that sometimes Bachmann fit the motor the other way up to that shown in the photos. This isn't immediately obvious to the eye, but will result in the model running backwards as it effectively reverses the motor connections. If you find your sample suffers from this problem, simply swap the orange and grey wires over - that's all there is to it.
Photo 11
Before putting the body back on the chassis it's as well to check that everything is working. The safest way to do this is to put the loco on the programming track and try and read information from the decoder - the instructions for your particular DCC system will tell you how to do this. If all is well (and I've never yet had a problem) then pop the body back on, taking care to relocate that bent bit of wire above the front steps. You've fitted the decoder at the front of the loco, so make sure you align the body with the cab to the opposite (rear) end. Finally replace the two screws (the longest one fits at the rear) and the couplings.
I took the opportunity to fit Kadee couplers at this point, using their number 18 which is a direct fit into Bachmann's NEM 362 socket. All that's left is to add the detail parts and renumber the loco - I don't want two 08623s.........