We don't have a published maximum axle weight or locomotive weight. Most locomotives fall in the 200lb or less per axle. We've handled a 2-1/2" scale Climax that was I believe 1,600lbs on four axles and Larry Goldby's 2-10-4.
Thinking about limits, here are a few to consider:
1. Vehicle limit for any nearby roads/bridges. Not likely to matter.
2. Vehicle limits to reach the unloading area. Things like turning radius, overhead, or road dips and bumps.
3. Length of lift, turntable or transfer table. Longest piece that fits.
4. Clearance plate for the whole railroad. High and wide limits. Signs, turnout controls, etc...
5. Length or weight limit for steaming bays.
6. Any weight limits around the track.
What I'm trying to say is the original question is down the road a bit from other limits that might exist. I doubt most clubs know all of these, but it is something worth considering and where possible accumulate answers.