Steering stem cracks

[mechanic]

Since I am totally sure I haven't caused the cracks when recently removing the lower cup, I'm wondering if it's anything to do with stresses generated by having a Ural chair fitted to the bike for the last 20k miles. Far greater lateral forces will be carried into the stem, plus the bike had a relatively hard time negotiating the poor roads and tracks of S. America over the majority of this mileage, thus generating further stresses into the frame/headstock.

The better photo just posted almost looks like the metal has been torn/stretched apart. Not cut mechanically with a chisel or cutting disc etc. Its an interesting one alright, but there will be an answer. Noteworthy what you have added about extensive sidecar use on poor roads? I’d love to see it in the flesh! Have you thought about having it dye tested for cracking/failure?

[Snaf MKII]

That looks like a work hardened fracture to me, bin it the material around the crack will be brittle. What are the fork guides like, grab the bottom of the fork and see if it moves in relation to top tube.
There are a lot of non design stresses on conventional forks with a sidecar bolted on, I'm sure you know that from riding all those miles.

[mark vb]

Yes, I fitted the new bearings.... I put the new cup in the freezer and fitted it using the original removed/cut cup as a 360 degree drift, tapping it gently down.

I get putting the outer races in the freezer before tapping them into the headstock, but wouldn’t putting the new cup in the freezer make it smaller and therefore more difficult to tap down on the stem though?
Or am I looking this wrong - which may be possible?

Yes, you're right, my mistake.... it's the races I put in the freezer to shrink them. The cups, if anything, could benefit from heated a little bit to expand them. For both the races and cups I tend to use the old items as drifts - with a cut so they come off easily.

[mark vb]

The better photo just posted almost looks like the metal has been torn/stretched apart. Not cut mechanically with a chisel or cutting disc etc. Its an interesting one alright, but there will be an answer. Noteworthy what you have added about extensive sidecar use on poor roads? I’d love to see it in the flesh! Have you thought about having it dye tested for cracking/failure?

Yes, that's how it looks to me, more of a natural tear. I will endeavour to take it further.... maybe I should in the first instance go back to the place (Merton College in S. London) where I did my C&G m/c certificates a while ago as I recall they had a material science dept who may be able to do some testing.
Unfortunately, seeing it in the flesh is now impossible! I separated the XRV from the chair several months ago and had my CRF1000 step-in to take over -

[mark vb]

That looks like a work hardened fracture to me, bin it the material around the crack will be brittle. What are the fork guides like, grab the bottom of the fork and see if it moves in relation to top tube.
There are a lot of non design stresses on conventional forks with a sidecar bolted on, I'm sure you know that from riding all those miles.

Yep, the cycle parts of the rig certainly get a far harder time than with a solo. Luckily, I've tracked down a used stem to replace the defective original one (new ones are now discontinued). The XRV is being put back to solo, with the forks currently on the workbench for a thorough check before being re-fitted.

[soho]

Hi Mark, I'm pretty sure that would be from torsional stresses transmitted into the head stock from those long AT forks and a 21" wheel. There were times with mine I just knew I was putting massive loads on the frame. I was down at WASP to look at some options, but without massive reinforcement, their over engineered forks would have been a waste on the AT. Off road outfits need over engineered frames too I've learnt !

IMG_1885.JPG (177.44 KiB) Viewed 1047 times

I tried all kinds of heavy duty stuff...........!

IMG_1372.JPG (158.64 KiB) Viewed 1047 times

[mechanic]

The better photo just posted almost looks like the metal has been torn/stretched apart. Not cut mechanically with a chisel or cutting disc etc. Its an interesting one alright, but there will be an answer. Noteworthy what you have added about extensive sidecar use on poor roads? I’d love to see it in the flesh! Have you thought about having it dye tested for cracking/failure?

Yes, that's how it looks to me, more of a natural tear. I will endeavour to take it further.... maybe I should in the first instance go back to the place (Merton College in S. London) where I did my C&G m/c certificates a while ago as I recall they had a material science dept who may be able to do some testing.
Unfortunately, seeing it in the flesh is now impossible! I separated the XRV from the chair several months ago and had my CRF1000 step-in to take over -

Thanks for the photos. However, when I said I’d like to see it in the flesh I was referring to the steering stem ! I look forward to reading of more developments. Good luck.

[mark vb]

Thanks for the photos. However, when I said I’d like to see it in the flesh I was referring to the steering stem ! I look forward to reading of more developments. Good luck.

Well, if ever you're in the east Kent area you're welcome to call in and peruse the stem over a coffee - it will probably be mounted on the wall in the garage, a sort of modern-day deer head, a tribute to the outfit's adventures in far-off lands !

[mark vb]

Hi Mark, I'm pretty sure that would be from torsional stresses transmitted into the head stock from those long AT forks and a 21" wheel. There were times with mine I just knew I was putting massive loads on the frame. I was down at WASP to look at some options, but without massive reinforcement, their over engineered forks would have been a waste on the AT. Off road outfits need over engineered frames too I've learnt !

Yep, I hate to think of the extra stresses put on the old AT. I guess it's done pretty well getting this far.... who knows how long the stem would have gone on if I hadn't had to change the bearings.
I kept the standard XRV forks but changed the 21" wheel for a slightly wider 19" to increase rigidity and enable a square tyre to be used. Maybe leading link forks would have been the way to go?
The CFR has also now got a 19" wheel and has kept the standard forks, which being USD should have more rigidity. I hope.

[Snaf MKII]

I keep coming back to look at this, are there two cracks oposite each other and slightly offset from the straight ahead position?
I'm thinking that the largest load is turning left where the weight is transfered forward and to the right hand side and that appears to be the plane that the damage is done.
I've never had a close look or ridden a sidecar with conventional forks but I'd have thought the rake angle would lift the front tyre towards it's edge using a flat carcase tyre.