I have started the build of my new loco, a RhB Ge2/4 in 1/8 scale on 5" gauge. Two motors, each driving one axle, the two axles coupled with rods, the same arrangement as currently running on my first box-cab electric with 5 tpi toothed belts.
The two gear motors purchased, Unite 450 W, 24 Vdc, 420 RPM, came with a 9-tooth 1/2" x 1/8" chain sprocket fitted, so it seems obvious to experiment with chains.
The local bicycle shop suggests that a 1/2" x 3/32" chain would be adequate. Does anyone have operational experience that this size would be adequate ? Do chains commonly come in metric sizes ?
Wheel speed at 8 km/h is 321 RPM, so a reduction of about 0.6 is required between motor and wheel, or about 12-tooth if I use the existing motor 9-tooth. But, fitting a sprocket to the axle is unknown at the moment and will, inevitably, involve boring out to suit the axle. As the axle is provisionally 20 mm to suit the prototype, I will probably be forced into increasing teeth count just to fit the axle. Guidance in this area gladly received.
Seems like no-one wished to offer comment on your enquiry.
9-tooth sprockets carry quite a high tooth loading with consequential increase in wear rates. I'd suggest you fit sprockets with at least twice that number of teeth as a minimum since this will reduce tooth loading and also make chain slackening, due to wear, less of a problem. I'd also suggest that at least one of your sprockets has a prime number of teeth (17, 23, 29 etc) to prevent the sprocket pairs setting up a cyclical wear pattern. Such wear patterns mean the chain runs tight-slack-tight on alternate teeth and exacerbate wear rates and noise
I'd stick with 1/2 x 1/8 chain since the wider tooth again means less wear.
If you are fitting a tensioner idler sprocket ensure it is mounted on the 'return' or 'slack' side as defined for normal forward running but ideally you should avoid tensioners if at all possible and make the motor mounts with slotted holes to permit adjustment. I take it you are aware that you can also get "1/2 links" for adjusting chain lengths. A normal chain length adjustment requires 2 links added/removed which for a 1/2 chain means 1" of adjustment. But with the special 1/2 link you can get down to a single link (1/2") adjustment. see here for example rollerchains.co.uk/06b-1-no12-chain-half-link-38-pitch-bs-simplex-788-p.asp
Edit : Just realised your original post was in 2015 I trust you got your drive chains resolved
Edit 2 : Should have emphasised the use of term "adjustment' related to total chain length, not length of slots in motor mount. - Must do better !
2 links added results in the length of the chain increasing by 1" on a 1/2" pitch chain, but that is shared by the 2 runs of the chain, so the adjustment only needs to be equal to a single pitch of the chain (1/2").