Converting the Heljan Class 128 single parcels unit to P4
Entry posted by Captain Kernow
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When I saw someone else bring their model of the Heljan Class 128 into DRAG one evening (still in OO), knew that I was going to have to concoct a plausible excuse to run one in the Bristol area, so that 'Callow Lane' might see one of these beauties in due course.
I did manage to pull together some reasonably convincing lies historical accounts as to why one might have been running to and through Callow Lane, but I'm blowed if I can remember what they are at the moment.... 
Anyway, I duly obtained one of these beasties (which weigh in at a cool 634 grams!), got it home, took it out of the box and admired it. I even posed it on Callow Lane in OO mode and took a couple of snaps. I then put it away and got busy with other stuff, mostly work and the planning for the Scalefour Society AGM at Holcombe on 22nd June last.
Anyway, back to the plot... I managed to get some time this weekend to have a look at the prospects for conversion.
I had already established that I had four axles of Branchlines 'Black Beetle' 12mm turned nickel silver wheels, which would fit the Class 128. One question was whether there would be sufficient room between the bogie frames for P4 wheel sets...
As it turned out, there wasn't quite enough room for P4 wheels to rotate freely. This being Heljan, the bogie side frames do come off fairly easily, and bearing this in mind, the solution (with hindsight), would have been to simply washer out the frames by no more than 0.5mm each side, possibly even less. Of course, I adopted a more Heath Robinson-ish and time-consuming solution, because I only thought about the washering idea after I had finished the conversion...
Taking each bogie in turn, the keeper plate comes off fairly easily by prising at least 3 or the 4 retaining clips (there are two on each side of each bogie):
So, this is what it looks like without the keeper plate in place (warning - lots of lubricating grease!!):
All axles are driven, in common with other Heljan locos. Each axle comes out easily. Due to the fact that no one has yet (to my knowledge) produced 'drop-in' conversion packs for this unit, the Heljan drive worms would need to be recovered from the OO axles and re-used with the Branchlines wheels.
First of all, the wheels are removed from the OO axles (I used my NorthWest Short Lines wheel press) - a wheel press/puller of some kind will make this job easier.
The drive worm is then removed from the OO axle, also with the wheel press (they are a very tight fit, as you would expect):
Next , get the Branchlines 12mm P4 wheels ready:
I do have some stub axles in P4 (Ultrascale ones ) somewhere, but I just couldn't find them. Clearly the pin-points would have to be removed if using these axles, which was just as well, given the treatment that was meted out on them by the wheel puller...
Once the remains of the pin point axles had been cut off in a vice and the ends cleaned up and slightly chamfered, you are left with this:
The short section of brass tube in the above photo (it is 8.25mm in length) is to help fit the Heljan final drive worm onto the replacement Branchlines axle, more of that anon.
First of all the final drive worm is introduced to the Branchlines P4 axle (the photo shows a GW Models wheel press being used):
Using the hardened steel plate from the NorthWest Short Lines press, the purpose of the brass tube now becomes clear, as it acts as a jig to ensure that the tightly-fitting nylon Heljan worm goes exactly in the middle of the P4 axle:
Completed P4 wheel set, ready to be fitted back onto the bogie:
However, before you can put the P4 wheels back in, there is the matter of the inner faces of the bogie side-frames to consider. The Heljan brake blocks also need to have some plastic taken off the inner rear faces, to avoid a potential contact with the P4 flanges. Given that the additional clearance needed is certainly no more than 0.75mm to 1.0mm, the easiest solution would be to washer-out the side frames, and thus provide the additional clearance. Of course, I didn't think of that at the time, so I filed lots of plastic off the inner bogie side frames...
Eventually, you get a more or less completed P4 bogie:
The completed conversion poses on Callow Lane, where I'm happy to say that it runs (in P4 mode) as smoothly as it did in OO mode...
My main concern with this unit was whether it would fit in the tight confines of the goods shed, bearing in mind that the rail doorways are rather narrow. Well, the Class 128 does fit (both ways round tested!), but it is very, very tight...!
After that, having established that it ran OK on all parts of the layout, I took a few more photos:
So, this isn't a fancy, sprung or compensated solution, but the sheer weight of these models will ensure that this keeps on the track, hopefully all of the time!
I've yet to weather it, of course, and the next job is to fit screw couplings and make a bespoke box for it, but I'm happy with the outcome. It is so heavy that it makes a satisfying noise as it runs over the rail joints!
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