The first question some of you might ask is, "Why would you want to put a air cooled XR400 engine in a modern chassis?"
The answer is reliable torque.
Ever rode a XR400?
If so, then you know that for their size, these engines are torque monsters.
You will also know that these engines are utterly reliable.
Put a nice exhaust on one, jet it correctly, and ride it, ride it, ride it........Change the oil, clean the air filter....ride it, ride it, ride it........
For tight trails with ruts, rocks, and general mayhem, a low geared, high torque engine just makes the trip a lot easier.
The problem with the XR400 is the chassis is dated.
Let's face it, the xr400 chassis design is how old?
Let's see, they first started making them in 96 and stopped in 03.
Even then the conventional forks and marginal brakes were already dated.
I'm getting older so I don't feel the need to shift, shift, shift, smoke clutches, and wind the springs out of a modern 4T engine while riding on single track, rutty, rocky, trails.
I want to leave it in third all day and let the torque pull me through.
Yet, when it comes to jumping, handling, and braking I want the best I can get, and the XR400R chassis is not it.
So, I decided to see what would be involved in making this conversion happen.
First, here is a picture of the XR400R engine cases with the cylinder, sitting in the CRF250R frame.
Right off the bat a few things became apparent.
This would not be a easy conversion and I do not feel as though it would be practical.
Here are a few reason why.
You would need to cut the front part of the frame and extend it to allow for the longer engine cases.
I do not even have the engine sitting as far forward as it would need to go in order to get the swing arm pivot pin to slip in.
My guess is that the engine would sit about another 1.5" forward:
The next problem is the head is simply to wide to sit in between the main frame rails:
The next question I would have is the location of the kick start.
I'm not 100% certain but I believe that the kick lever would be sticking on the outside of the frame.
This would be dangerous, look bad, and eventually wear a hole in your frame.
In my opinion, this idea is a bust.
So, what about putting a XR400R engine into a CRF450R chassis?
When I get another CRF450R chassis in, I'll let you know
