I doubt that it is even remotely possible to build a motorcycle from from bones that have been dipped into stainless steel. Even if the stuff stuck to the bone and solidified the results would have no structural integrity.
Is it "built from" bones, or are the bones ornaments on a steel frame. My sense was that the bones are decorative elements that don't bear weight.
As for temperature, keep in mind that it takes time for two bodies to reach a temperature equilibrium. The bones become ash when the bones
reach 760 - 1150, but putting them in a 1400 degree medium doesn't mean they're immediately 1400 degrees; any more than putting your 72 degree f turkey in a 400 degree f oven makes the turkey -- at that moment -- 400 degrees. Think of how long it takes for that turkey, surrounded by a 400 degree medium, to reach an internal temp of 150 and have the thermometer pop up.
That's not to say that steel-plated bones are possible, it is simply to say that the threshold temperatures -- themselves -- aren't enough to make it impossible. What happens to the bone depends on how much mass the bone has, what its temperature is, how much mass the steel has, what its temperature is, and how long the two bodies are in contact
. That would allow you to calculate the temperature of the bone. If that number is greater than 700, it is ash.
It is conceivable, to me, that you could dip a bone in liquid steel for less than a second and have it remain under the cremation point. Once it is out of the pool of steel; the liquid steel around it has very little mass compared to the mass of the bone. That steel is still in the 1400 C range -- because temperature is an average of the heat within a body -- but the total amount of heat is very little and I can easily see them coming to equilibrium under 700.