This is a question that I struggled with so thought I would share what I discovered for others that might have the same issues. The origin was my desire to fit an N scale trolley on a small platform on a shelf under a glass topped kitchen table with limited space, 2' x 4', and running the streets of a town. I had neither the space nor desire to run non-scale radius turns and suspect this has limited others who might desire to have a trolley on their board. Radius for trolleys can get down to some pretty tight numbers to negotiate city street corners, something I remembered clearly as a kid in Pittsburgh where you would here some ungodly sounds as the trolleys negotiated some of the tighter turns on city streets. I found some real radius numbers on line for Philadelphia's streets that were down to 33' radius in some places which scales down to about 2 7/16" using 1/160th scale for "N". That was what I needed, something in that range, and it was WAY tighter than the available trolleys were capable of. The standard issue PCC trolley seems to be designed for 7" R. (according to "Bach-man" in this thread), and the Spectrum series, which is a totally different design, can get down around 4 1/2", maybe a little better (according to some remarks from Spookshow in another thread as well as the previous response mentioning 4". Was that at C/L?). Neither of those was near tight enough for my purposes or even for true scale. I decided to buy a PCC and see what I could see, maybe modify to get it close enough. Not to be. The design with worm gearing can't be modified to turn the truck anywhere near the number needed as the turn is accomplished simply by letting the worm gear misalign with the truck gear. This was also one of the fundamental differences between the standard line and the spectrum model which uses drive shafts and universal joints, affording a tighter turn radius (4 1/2"?) than the basic model (around 7"?). After contemplating and reluctantly preparing to scrap the idea I recalled a similar issue with an HO set-up some decades ago where it was solved by running an early design trolley with only one axle at each end. No truck to turn, the wheel flanges just guided the trolley through and at some very tight numbers. Looking at the body design and how much it skirted the truck, having them not very visible, I decided to modify this truck to run this way, straight on on just two axles. I was sure it would negotiate much tighter but not sure if it would be enough.
The modification was actually pretty simple and worked quite well, tested negotiating a 1 1/2" radius, made with flex track. Yes, 1 1/2" @ C/L of track. That's a life size 20'R, even tighter than I will likely use. I will probably use 2" or so which is life size about a 27' R and perfect for my needs. Double track on a 2 1/4" or so street with very conventional small radius sidewalks, no overhanging those, hitting pedestrians or buildings. The purists might find non turning trucks to be sacrilegious but I find it looks fine in operation, hardly noticeable with the trucks being skirted as they are, and certainly suitable for my purpose with the only real option being to scrap the whole trolley idea. It also doesn't require any modification to anything but the truck itself so is easily undone for the price of two trucks, $3.50 each from Bachmann parts.
The modification requires 1) disassembling the truck assemblies to remove the wheel flanges and most of the wheel diameter from one axle on each truck and 2) fabricating a plastic piece that glues on to the truck body. The plastic piece serves as a spacer between the truck and frame at the end of the truck with the cut down wheels to limit the truck "float" so that those wheels can no longer touch the rails. Further, it has a thin projection that slides up between the frame halves to prevent rotation. This glue on piece I made from ABS. Having access to a lathe, I machined this part as a ring and then cut in fourths yielding parts for four trucks. It can be just filed and Dremeled as well but when you've got a lathe...
The dimensions of the part I machined were adequate proportions to glue on then file and trial fit to finish. Sketching the part with the dimensions and looking at the actual truck should be all that's needed to understand what's being done as well as adequate dimensions, whether hand making or machining.
The ABS part as I made it was machined from 5/8" round bar. It would look like a bushing with a drilled hole and a raised flange/ ring centered on its diameter. The total width is .20". The hole through center is 23/64" drilled. The major diameter of the ring centered and used to dog between frame flanges was finished at .610" diameter and was 1/32" (.031") thick. The diameter turned from each end was .485" diameter, leaving 1/16" wall thickness from the I.D. That ring was then cut into quarters, yielding four parts. Glue on with solvent cement, trim with a file as needed checking level of truck ride height and making sure the center dog floats freely in the frame groove. This still allows the truck to float slightly, following track irregularities. File fits are all that's needed and those dimensions leave enough for that. If you're just hacking it from a block, a sketch as described above will also yield the dimensions needed to make the part.
A couple of additional notes. 1) To cut down the wheels, pull them out of the truck gear and mount them in your drill. Turn on and file. Remove the flange but also a good bit of the wheel. As long as there's a visible wheel center filling the space it's not very visible once fully assembled with the body skirting the truck, so don't be shy. 2) If you're using extremely tight track radius as you will now be able to do, that wheel can span to the other side of the track mid turn and if able to contact, that's a short. Make sure it's clearing the track in your file/ fitting time with the glued on spacer block. 3) To remove and reassemble the wheel with reasonable assurance of not splitting the delicate plastic gear, warm those parts in hot water. Pull the wheels out with your fingers. Warm the gear again for reassembly. Don't squeeze the wheels together too hard. They should register nicely with minimal effort and warmed parts. 4) The modified trucks can be assembled with the drive wheels assembled either forward or rearward or a combination of one forward or one rearward. It doesn't effect the operation of the trolley but it does effect how it acts in the corner as it effects the wheelbase. With the modification completed you can assemble different combinations and see what works best for you or fits your fancy. I found that the rear truck assembled forward and the forward assembled rearward gave the shortest wheelbase and nicest action. I think that's it. A careful read while looking at the actual parts should be enough to understand and some simple enough tools should be enough to execute the modification. And if ever you want to undo it? Two trucks from Bachmann, DONE! Hope that helps someone.
The modification was actually pretty simple and worked quite well, tested negotiating a 1 1/2" radius, made with flex track. Yes, 1 1/2" @ C/L of track. That's a life size 20'R, even tighter than I will likely use. I will probably use 2" or so which is life size about a 27' R and perfect for my needs. Double track on a 2 1/4" or so street with very conventional small radius sidewalks, no overhanging those, hitting pedestrians or buildings. The purists might find non turning trucks to be sacrilegious but I find it looks fine in operation, hardly noticeable with the trucks being skirted as they are, and certainly suitable for my purpose with the only real option being to scrap the whole trolley idea. It also doesn't require any modification to anything but the truck itself so is easily undone for the price of two trucks, $3.50 each from Bachmann parts.
The modification requires 1) disassembling the truck assemblies to remove the wheel flanges and most of the wheel diameter from one axle on each truck and 2) fabricating a plastic piece that glues on to the truck body. The plastic piece serves as a spacer between the truck and frame at the end of the truck with the cut down wheels to limit the truck "float" so that those wheels can no longer touch the rails. Further, it has a thin projection that slides up between the frame halves to prevent rotation. This glue on piece I made from ABS. Having access to a lathe, I machined this part as a ring and then cut in fourths yielding parts for four trucks. It can be just filed and Dremeled as well but when you've got a lathe...
The dimensions of the part I machined were adequate proportions to glue on then file and trial fit to finish. Sketching the part with the dimensions and looking at the actual truck should be all that's needed to understand what's being done as well as adequate dimensions, whether hand making or machining. The ABS part as I made it was machined from 5/8" round bar. It would look like a bushing with a drilled hole and a raised flange/ ring centered on its diameter. The total width is .20". The hole through center is 23/64" drilled. The major diameter of the ring centered and used to dog between frame flanges was finished at .610" diameter and was 1/32" (.031") thick. The diameter turned from each end was .485" diameter, leaving 1/16" wall thickness from the I.D. That ring was then cut into quarters, yielding four parts. Glue on with solvent cement, trim with a file as needed checking level of truck ride height and making sure the center dog floats freely in the frame groove. This still allows the truck to float slightly, following track irregularities. File fits are all that's needed and those dimensions leave enough for that. If you're just hacking it from a block, a sketch as described above will also yield the dimensions needed to make the part.
A couple of additional notes. 1) To cut down the wheels, pull them out of the truck gear and mount them in your drill. Turn on and file. Remove the flange but also a good bit of the wheel. As long as there's a visible wheel center filling the space it's not very visible once fully assembled with the body skirting the truck, so don't be shy. 2) If you're using extremely tight track radius as you will now be able to do, that wheel can span to the other side of the track mid turn and if able to contact, that's a short. Make sure it's clearing the track in your file/ fitting time with the glued on spacer block. 3) To remove and reassemble the wheel with reasonable assurance of not splitting the delicate plastic gear, warm those parts in hot water. Pull the wheels out with your fingers. Warm the gear again for reassembly. Don't squeeze the wheels together too hard. They should register nicely with minimal effort and warmed parts. 4) The modified trucks can be assembled with the drive wheels assembled either forward or rearward or a combination of one forward or one rearward. It doesn't effect the operation of the trolley but it does effect how it acts in the corner as it effects the wheelbase. With the modification completed you can assemble different combinations and see what works best for you or fits your fancy. I found that the rear truck assembled forward and the forward assembled rearward gave the shortest wheelbase and nicest action. I think that's it. A careful read while looking at the actual parts should be enough to understand and some simple enough tools should be enough to execute the modification. And if ever you want to undo it? Two trucks from Bachmann, DONE! Hope that helps someone.