Originally Posted by JAB
I've got a '91 also. Is the swap worth it and is it a bolt on deal?
The older CR forks are an easier swap than the newer CRF forks as the older CR stems share the top bearing size and stem length with the XR600. The 1989 CR500 actually shares both bearing sizes but the 1989-1991 USD forks are sub-par.
The swap is really easy.
1) Remove forks and top clamp from CR500
2) Take bottom clamp, stem, and top bearing to your favorite local machine shop, pay them $40 to press the stem out, machine the bottom bearing area on the stem to fit the top bearing, and press the stem back in
3) Reuse the XR600's bearings, reassemble fork and bolt on
There are some issues with the USD forks...
1) CR500 forks have the pinch bolts facing forward. Some other CR and CRF forks have the pinch bolts on the rear causing problems clearing the stock tank. I have a stock, a 4.3 IMS, and a 5.8 Acerbis and there's no real problems with fork/tank clearance using 1995-1996 CR500 forks.
2) The USD forks are slightly longer (3/4" if memory serves) and sit a touch higher in the stroke. It choppers out the ride a touch even with the forks pulled all the way up. I'm going to compensate for this by raising the rear of my 1991 with a shock off of a 1986 XR600 which (if memory serves) is 1/4 inch longer than the newer ones.
3) The CR500 top clamp has rubber mounted bar clamps. These sit a touch higher than the stockers and I ran out of free play on the clutch and had to move it 3" toward the center of the bike.
Other than that, it's like the forks were meant to be on there. The steering stops even line up. Some people re-use the XR600s wheel and brake. I just got them off eBay ($40 wheel/axle, $10 front brake with bolts). Fender bolt patterns are the same. The stock XR600 headlight straps will stretch over the larger CR tubes but will put up a fight going on and off.