You are right to think that the 250mm rotor is under sized.
What I am really gobsmacked by is your mix and match of the steering head bearings. You cant interchange races and bearing cages just like that. It is dangerous. If the bottom of the axle is 30mm then get someone to turn it down to the 28mm required. Dont mess about with these things, its you life. Please do not be offended I am just trying to stress the facts.
If the steering axle is hollow then maybe that is a bit of a problem if it is aluminium. If steel then just turn it down.
You will have to turn the spacers and get a different front brake caliper. The brembo one is abit dated and you will have difficulty finding hangers for it.
The steering/ignition lock is a bit of a problem. Dont know what the yama clamps look like but avoid drilling holes in them like the plague if they look cast.
Just so you know I am not bulshitting you on the above points, I have spent 4 year(ever since I got my dakar) trying to find a quick way to add usd forks to it and I have done it.
Originally Posted by JDRadman
I have begun the transformation.
I purchased a set of 03 YZ forks (46mm) and will fit the BMW OEM wheel and brake. I prefer to use the larger thicker 300mm disc rather than the Yamaha 250mm-stock rotor. Oversize 270mm off-road and supermotards kits get expensive pretty quick.
Confirmation for those contemplating such a modification on the bearing swap:
The Yamaha bottom bearing has a 30mm bore and uses a larger cup OD and is a bit taller than the 28mm on the BMW. It does however fit into the smaller OEM cup quite well. I used the stock Yamaha seal and bearing with the BMW cup. If you cut the rubber lip off the bearing seal it fits nicely into the recess left to create a good seal. Grease will complete the seal very close to as good as the stock BMW but not as good as the Yamaha OEM set up.
The top bearing is the same and I used the Yamaha top seal with a little bending to reduce the gap and greased it up well.
The fender mounts under the front triple within about 5mm if you cut off the number plate tabs and drill new holes. I also made a strap to reinforce the attachment of the front of the fender. The front mounting holes are very close to the front of the fender and not as wide as the OEM holes. It seems to work well so far in mock ups.
So now my challenges are
1)Key and lock mounting position
2)Spacer and new bearings for BMW front wheel
3)Hanger for BMW brake
I have some minimal machining capabilities at the house so I will start on those challenges this weekend.
If anyone has ideas on the key and lock would love to hear itů
If you completed this project and have additional details or ideas on any part of the process please share them.