Hi! Been a member since December (rhyme not intended) but this is my first post.... Forum seems like an excellent font of knowledge and has been incredibly handy thus far so many thanks!

However I've a question that I don't think has been covered before.... Has anyone ever heard of anyone "extending" the length of a steering head tube on a dirt bike frame? Seems to be more a bicycle thing according to google...

My mk1 RK CRM has an extension piece that's been machined to fit into the bottom inner bearing race recession at the bottom of the head tube! It's not welded but it is a tight fit, not interference but snug... I think it's been done by the previous owner so that CR250 yokes and steam currently fitted could just be bolted on as the CRM has a shorter head tube than the CR.

Just wondering if it's safe? Or would possibly result in diminished bearing life? Geometry is obviously going to have been thrown off as well

Sounds like some home brew engineering by a taller rider to overcome the MK1's inherent diminutive dimensions, and the backache they induce in some riders.
Mike

With the nut tightened on the shaft it should load all the bearings into the tube.
When the front wheel comes down from a jump/wheelie or goes over a bump the load should be up through the axis of the steering head (some of the force can also act as a lever through the steering head twisting the forks forward and up)...
however when you are hard under brakes the force decelerating your bike through the front brakes/tyres will act like a lever on your steering head bending the forks towards the rear. If the extension were brazed or welded in place there would be no chance that it would move. With the extension being a snug fit it will transfer the forces to the walls of the original bearing cup.
Have a look at the extension for any fretting wear where it sits in the cup and for any fretting or cracks in the head tube.
Depending on the quality of work and the type of riding you do it may/may not be ok.

The better option would be to get the yoke shaft machined to the shorter length to suit the head tube.

Don't forget there are considerable loads going through that part of the bike.

The thing to do is to swap the steering stems. I had a MK1 and did this to change the yokes and fit new forks.