Weights for Locomotives

Most conversions of this nature put the electronics in the tender (including antenna), then make use of a tether (not a hard thing to install), so your weight could stay where it is. I'm sure that you know all this, so I wonder why you are going this way.

Pretty much what D500 said. That’s a lot of work for such little gain.....pack everything in the tender, then either isolate the tender shell from the frame with tape and nylon screws, or come up through the coal pile with the antenna, and bury it it thin layer of “new” coal......fab up a tether, and roll............Pat

To answer your original question, to get more weight in the same volume of space, you'll need to use a material with higher density than the zamac the factory weight is made of.

First- I would try it without the weight.  You might be surprised, it may be able to pull the desired load.  Since the 1990 Hudson DOESN'T have rubber tires (love!), a little wheelspin is prototypical.

Second- among common materials the most obvious choice is lead.  Lowe's and Home Depot used to sell lead chimney flashing.  It looks like a stovepipe hat.  You have to cut the stack away from the base.  Then you can unroll the stack and cut strips (laminations) to build up the shape of the weight you want.  It takes a lot of planning and cutting.  You can adhere the laminations together with rubber cement.  Another approach with lead, is to make a mold out of wood or plastic in the shape you want, and fill it with a mixture of buckshot and white glue.

A more exotic material is "Wood's metal" aka Cerrobend.  It's a lead alloy that melts in boiling water.  You can buy it from specialty suppliers online.  You'll still need some kind of mold to shape it.

I agree with the others who advised you to put the electronics in the tender.  Ditch the original sound and go with ERR sound, then you'll have plenty of room.  It's better to "float" the tender (insulate the shell from its frame with Kapton tape all around) and use the whole shell as your antenna.  Don't fool with the handrails or trying to bugger up the coal pile.  Been there, done that, and it doesn't work as well.  Hope this helps!

You can buy lead sheet from Amazon

I had to add weight to my HHP-8, I took a "shot" and added it this way.

The bullets are 200gr .45ACP, and they had lousy accuracy, but the work great at weights.

some other posts have suggested stuff (including the above stuff,) like BBs glued in place, fishing weights, car tire weights, I've even used pennies. I didn't have access to GRJ's bullets! Hot melt and/or double sided foam tape also works.

I'd agree with moving the main board to the tender if you could.

Lastly, I have cut, shaped and moved around the original weights to gain room.

It's nice to hear that there's an O scale 3 rail loco out there without tires on it! Hey, I never knew. 

I've chopped a lot of weights in brass locomotives to fit stuff, many times to get fan driven smoke in, I have to hack the weights.  For tender weights, lots of times I have to remove the stock block and do different weights to fit with the expanded electronics.