I want to put a 1000 Watt 48V front hub motor kit to make an ebike. The problem is I only have 3.5 inches between the front dropouts and the kit requires 3.9 inches. Is there any way to widen the forks to fit the kit? The forks are aluminium and suspension.
You're best off using a rear hub kit with 1000Watt. The maximum power of a front hub kit would be 250 - 350 Watt. Any more that that and you put too much stress on the forks. If you look at the geometry of the rear drop outs you have a triangle design for strength. There is no triangle design on the front forks and drop outs. So now image a powerful motor on the front forks. It will put a lot of force on the front forks because as the motor is pulling, the forks must pull the entire weight of the bicycle and the rider along with it.
A front drop out failure is considerably more dangerous than on the rear. I've seen pictures on forums every now and then but have never seen it in real life. You should never put a powerful motor on aluminium forks.
As stated above it is much safer to put a powerful ebike hub kit on the rear drop outs due to the extra metal. Front suspension forks are very weak when compared with the rear drop outs. If something breaks on the rear you are much less likely to go over the handle bars.