Question: parts filled with putty for motorcycles

Under Motorcycle WIP I see a lot of bike's frame parts such as swingarms filled with putty to be more realistic. My experience with gray putty bought at USA hobby shops is that after curing it cracks, deforms and after sanding, I have to fill again the cracks, sand and do this few times until I get somewhat of a smooth surface. Too much waisted time for not a nice smooth surface for my liking. I know I'm missing on something that is out there. Instead I see some of you all in here with swingarms filled with a material that looks like a poly with clean lines and an ultra smooth surface. I was wondering if there is a product out there that could make my life easier that will look good too without lots of work. Thanks in anticipation of anyone's reply!

It sounds like you are still using solvent based "1-part" putty. The solvent evaporates when exposed to air hardening the solids (and unfortunately shrinking). Adding to the problem is the need for longer shelf life demanded by retailers which translates into lower solvent volatility and protracted drying time. To fill or build up any area or volume of significance I'd suggest using "2-part" putty. It works like epoxy. You mix two different colored putties together before using it. When the two are mixed together a chemical reaction takes place "curing" the putty instead of "drying" like the "1-part" stuff. Since nothing evaporates it stays the same volume. I'm sure others will chime in with their favorite products.

It sounds like you are still using solvent based "1-part" putty. The solvent evaporates when exposed to air hardening the solids (and unfortunately shrinking). To fill or build up any area or volume of significance I'd suggest using "2-part" putty. It works like epoxy. You mix two different colored putties together before using it. When the two are mixed together a chemical reaction takes place "curing" the putty instead of "drying" like the "1-part" stuff. Since nothing evaporates it stays the same volume. I'm sure others will chime in with their favorite products.

Thanks for your posting... Yes, you are right, I'm using one part putty. I'm new to this, still learning but I learn a lot among people just like you, thanks! What type of two part putty you recommend? I heard of Magic Sculp Putty, is this good?

I'm using Milliput right now. I consider it "good enough" but honestly there are some problems with it. Cost, short shelf life, crumbling. I've heard good things about Magisculpt but have yet to get my hands on some so can't comment based on personal experience. Tamiya has a product available too but I haven't tried it either. That's why I am hoping others will chime in.

I'm using Milliput right now. I consider it "good enough" but honestly there are some problems with it. Cost, short shelf life, crumbling.

I love Milliput mainly for its material qualities.
I love how it sands and how you can shape it when wet and all that but yes, there are a couple of issues; the biggest for me being that it absorbs moisture so really needs a proper sealing primer over it or else you risk colour variations over it.

Best I've tried is still Tamiya's epoxy putties.

I mostly use modeling clay hardening in the air for such big parts to fill, and often finish by a putty coat on surface.
Clay is easy to work with and cheap.
result is fine especially if completed by putty on surface when needed.

I'm using Milliput right now. I consider it "good enough" but honestly there are some problems with it. Cost, short shelf life, crumbling. I've heard good things about Magisculpt but have yet to get my hands on some so can't comment based on personal experience. Tamiya has a product available too but I haven't tried it either. That's why I am hoping others will chime in.

Read that the Tamiya putty gets on your hands and is not easy to take off. People are complaining about it. Doesn't matter what I use, I always use surgical gloves.

If your just filling things you can use regular old bondo for cars.
Play with the amount of hardener till you get it the way you want it.
But remember more hardener means you have less time before it dries