Steering stem cracks

[mark vb]

I went to renew my XRV's steering stem bearings the other day. When I took off the lower bearing cup from the bottom of the stem, I found three cracks (or splits? or fissures?) as shown in the pics.
When I posted on the FB XRV page, no-one answered my query asking if anyone had come across this issue before.... some said replace it and others said it's fine.... the usual FB conflicting advice, which I hadn't asked for!
So, has anyone here come across this issue before? If so, any theories on causation?
Luckily, I have a used stem on its way to me from a nice XRV parts specialist in Greece - new ones are discontinued. I was beginning to think I might have to get the defective stem welded-up and ground - which I may do so I have a usable spare.

[redbikejohn]

The horizontal marks? Looks like the previous owner or shop used a grinder to cut the bottom race to get it off and nicked the stem.

[mechanic]

As above. Certainly don’t look like time occurring cracks to me.

[mark vb]

Mechanic & Redbike John -
I've owned the bike from new, and have changed the bearings only once before at around 10 years ago when the stem was in perfect order. So it's happened between then and now.
When I took off the bearing cup off the other day I was careful so as not to damage the stem, so they are definitely not caused by my Dremel (which I used to make a partial cut across the cup, then a chisel to make a final blow to crack the cup; also, the two main cracks are on opposite sides of the stem whereas I used my Dremel in one place only and at a distinctly different angle to the horizontal line of the cracks in the stem).
It's a mystery, as Toyah once sang

[mechanic]

Hi again. Yes I hear you. It’s hard to give any further advice with regard to the marks seen on a photo as opposed to real life. At the end of the day it’s a safety critical item. You know what you have to do! It’s certainly an interesting one. Anyone else care to chip in? If you were on a certain ktm forum I’m sure you may well have an answer by now. If not, certainly many suggestions.

[mechanic]

Hi again. Just a quick thought. Did you fit the new bearings yourself or did you have a 3rd party press them on, if so they may have caused it somehow?

[Magnusson]

You see how the outside of the "crack" is wide and fatter near the bottom and perfectly straight. CSI tells us that it means it was caused by pointed impact from the outside. Pointing slightly downwards. Likely a chisel.
If it was caused by fatigue or stress by itself you would see uneven hairline crack that had no deformation on the outside.

[mark vb]

Hi again. Just a quick thought. Did you fit the new bearings yourself or did you have a 3rd party press them on, if so they may have caused it somehow?

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. Here's another pic of the main crack (there are two, one quite a bit bigger than the other. The third crack is roughly 180 degrees opposite, in a position between the two lockstops and where it would be virtually impossible to get a cutting wheel.
All three cracks are pretty much the same distance above the lower yoke casting, and all are virtually dead horizontal - so unlike damage one may expect from some random cutting/chiselling of the cup.
Anyhow, luckily I've found a used stem to fit . As for the cracked stem, I'm going to look into having the cracks welded-up/ground down so it's reusable at some future time.

[mark vb]

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.

[Saint rob]

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?