How can I correctly use BodyThrust?

So, I quickly created an engine model. It looks like this:

Engine Image

Inside that engine model there's a part called 'MainPart' - This part contains the BodyThrust.

MainPart Image

I just want my engine to constantly move forwards towards an invisible part in the model called ForcePart. Btw, everything is being welded to 'MainPart'

local bt = script.Parent.BodyThrust -- This script is inside of 'MainPart'
local engine = script.Parent.Parent -- The engine model
local force = 200
while wait() do
	bt.Location = engine.ForcePart.Position -- Setting the location property of the BodyThrust to the location of the ForcePart. 
	bt.Force = Vector3.new(force,force,force) -- Setting the force to 200 on each axis.
end

Now, this should work, but instead the engine spins out of control. It doesn't move forwards like it should. Please help!