2002 CR250 Cracked Frame Under Fuel Tank

@Bearuno

I’m used to seeing the crack up towards the top bearing area than the gas tank. Buddy has a 2007 it happened to and now makes me scared to buy a Honda around that time. 

That can be tigged up by any competent aluminum welder.  I’d take a drill bit and find the top of the crack and drill it out first to stop it from spreading.

They will all crack there eventually. My 08 did the same. Multiple posts about this. Can be prevented by filing the forging seam flush so it doesn’t set up a stress riser.  

The crack continues forward of the bolt hole. I would remove the triple clamps to make sure it doesn’t extend to the steering stem like mine did. 

I've done quite a few repairs on these (and other Alloy frames) types of failures.

Most common on the CRs, is splitting at the headtube.

A Key Point to remember is they are Bloody Old Frames. Stresses / Ageing of the Aluminium is cumulative. Pretty much all Aluminium alloys are age hardening, and work hardening. Thus, becoming ever more brittle. 

Throw in what can be years / decades of abuse, well, that they last so long, I find quite impressive.

The Headtube splitting is often down to owners letting the headset come loose - that really stuffs up headtubes, of Any metal type. Mind you, a classic that I had come to me was one where the idiot owner had refused to buy OEM, and had sourced a bearing that had something like a .5mm OD difference (larger). His thought was, well, Aluminium is Soft, it will compress.......... 'Ping', went the headtube....... I sent the Idiot on his way.

The stresses on the Head Tube 'Box' are quite complex. When you look down on the frame main beams, and you think a bit, you can see how the beams are prone to what I call 'un-egging'. Under extreme stress, the (rough) egg shape of the beams, can flex out to  a more circular form. It's why common crack points are at the Inside of the beam welds to the shock cross over, and / or  the inside welds at the headtube box, or, indeed, as seen here and so often, straight down the middle of the 'Box', through the raised casting / forging egress point. I honestly don't know what the process for the production of the headtube / box unit is.

I would Never, as a pre-emptive thing, remove that raised line. Though, it largely disappears with  the grooving and welding, of course.

Why - well, I'd love to have a headtube / box to cut up, to see the internal areas of those extruded lines, to see what is underneath / on the backside of those 'lines'. But, In my grooving of those areas, I've found a Lot of variations of the thickness to said areas. It seems there's an inconsistency that means that in some areas, there is full thickness at those points, but, in some areas there's quite a 'Divot' upwards towards the flat outer 'line'. So, a lot of stress variation / concentration on a part that is being 'torn apart', like how you open up a roll / bun / bread loaf.

Anyway, that's enough speculation / pontification. I'd just like to get a good look at the internals of the casting / forging one day.

So, for addressing the crack through the tank mount :

 Don't try to weld it up, re- drill and tap - Just Don't!

The original bolt mount hole is a perfect guide for use of a High Quality Holesaw. Just cut the entire mount out, and machine up a 'plug', pre drilled and tapped, to then weld into the 'box'. Groove / Angle at weldment points. 

The circular welding in of the tank mount plug, helps a lot with tying it all together.

Groove out the cracks (before the welding in of the Plug), I weld up the cracks Before I weld in the Plug . Some areas, the material can be that thick, that I'll do a succession of weld passes.  There's a remarkable inconsistency - as I mentioned earlier -   I've found with thickness. Some areas, can be damned near paper thin!

It pays also, to look Very, Very Closely at the weld points I mentioned at the Main Beams to HT Box, and Beam to  Shock Mount X over while you're doing the repair. I've often found cracking at the welds

And, as always, I urge people to let the frame 'sit' for a few weeks if at all possible. The (assumed - but the factories have such demands / order levels and power, to have truly 'special' alloys made for them) 7000 series alloys used, are formulated for such a 'rest' after welding. Most though, never listen to me, and throw the bikes back together. I've Not had a repair fail, thankfully, but it p***es me off to see blokes just throw things back together.

I've done a Lot of frame repairs over the decades - this is how I approach  and address such a  repairs, if I take it on. Mind you, I have often refused repairs - some frames are just so abused (or, I assess the owner as a f**king drongo that I want Nothing to do with) that I Will Not do the job. 

Yes, that type of Plug you've shown is The Go.

Just a little thing that can help is to make up a little plate to go across from the top of the spar welds, that you can bolt the plug to:

The tank mount, to my dim recollection, sits higher than the spar welds, but, while the original is still 'in situ', just  pack up the gap from the plate to the spar / weld, each side, mark where  the edges of the plate will be.  I've got many gauges of aluminium plate or steel to use, but something like a metal tape is fine to give final layers, and will handle the heat from the initial tacking of the Plug. A nice heavy weight like a socket or two, will keep the plug flat and even . It's bugger to get the plug a bit 'cocked', and have the tank a poofteenth skewiff at the end of a job.

I have a spare frame for an 02. I have Oregon title but I’ve never put it in my name. Pm me if you’d like to buy it

This, only other safe option imo is just replacing it.

Can the crack be seen from the bottom, OP?