Adventure Bike Rider Forum

A cheap DIY crack reveal is to soak some paraffin around area and clean it off with a solvent ...throw some talc around the area and it should show up where the paraffin is still weping out the crack
Have to say it still looks like a chisel mark where someone tried tapping or levering up the race than anything else (not saying thats what you did VB just what it looks like)

Asgard wrote: ↑Thu Feb 22, 2024 12:53 pm A cheap DIY crack reveal is to soak some paraffin around area and clean it off with a solvent ...throw some talc around the area and it should show up where the paraffin is still weping out the crack
Have to say it still looks like a chisel mark where someone tried tapping or levering up the race than anything else (not saying thats what you did VB just what it looks like)

I hear exactly what you say, and I'd probably be saying the same thing if it was someone else's stem. But..... the only person ever to remove the cup is me, and I have never used a chisel to try and tap/lever up the cup - I know this is a 'traditional' method, and it is indeed the method I was taught, but I don't particularly like it. The only chiselling I've done is a single, controlled blow once I've cut a groove in the cup, to break the cup. And that's at an angle to follow the cut, not horizontally across to the stem as the three 'cracks' are.
So, if I had caused the 'cracks' as a result of over-enthusiastic chiselling I would certainly have known about it at the time, and this thread would not be !
As for the view of a cutting wheel causing the 'cracks', the pattern of the 'cracks' would be impossible to produce by using a Dremel cutting wheel held in one position at an angle of around 30 degrees off the perpendicular.
It's certainly a bizarre situation, and one I am minded to try and get to the bottom of.

I’ve followed this with interest. I have every confidence in your mechanical ability. I’m still thinking. Excessive loading caused by addition of a side car bring ridden on rough roads. For me the stem has itself failed, the material literally being torn or stretched open, by forces way outside manufactures testing and expectations.Those are the lines I would be going down.

So, for those folks who have commented the 'cracks' are likely caused by over-zealous use of a chisel or nicks caused by an errant cutting wheel, I have here a pic of the cup.... the Dremel cut is at around 45 degrees (not 30 as I had said previously). The cut was cracked open by a careful blow using a chisel, again at 45 degrees as per the line of the cut. There is absolutely no way this process would have caused the three 'cracks' as shown in the photos I initially posted. And to reiterate, no-one else has attacked the stem with a wheel or chisel - I have owned the bike since new and have been the only person to take off the cup ! Ever!

No need for further explanation I knew you were a good tech before!

I think I can see an issue if not the cause, ball bearing are not suitable for anything but small radial loads. You should be using taper roller bearings that transmit the axial and radial loads that you find in sidecar applications.

I thought AT headstock bearings were Taper rollers as standard?

Just had a google apparently not, I only had one AT (RD07) didnt keep it long but did take the front end off to overhaul the forks and I'm sure it had taper Rollers

mark vb wrote: ↑Fri Feb 23, 2024 12:28 pm So, for those folks who have commented the 'cracks' are likely caused by over-zealous use of a chisel or nicks caused by an errant cutting wheel, I have here a pic of the cup.... the Dremel cut is at around 45 degrees (not 30 as I had said previously). The cut was cracked open by a careful blow using a chisel, again at 45 degrees as per the line of the cut. There is absolutely no way this process would have caused the three 'cracks' as shown in the photos I initially posted. And to reiterate, no-one else has attacked the stem with a wheel or chisel - I have owned the bike since new and have been the only person to take off the cup ! Ever!

Yea making dremel cuts around the circumference would be a rather odd technique for removing a pressed on ring, the marks on the steerer are obviously not that.

I really hope you find out what did this as its now doing my head in as well, I did a bit of metallurgy and some destructive testing (only on test samples) for my Aero Eng and have seen tears in Aluminium alloy when it gets past its yield point but they usually have a rougher surface and as mentioned there is no deformity around the fissure so it can't really be that.

Is it possible you just didnt see the defects when working on it previously? (I mean bought from new and knew you hadnt mistreated it so you wouldnt be looking for such a thing) as it occurs to me that if they were impact from a chisel type tool then there would be raised edge that would need to have been dressed off before fitting of a bearing, maybe in factory the race kicked and they had to remove it causing the damage which they then fettled and refitted the race?..Im flummoxed

I have an update....
A new-to-me steering stem has arrived from Greece (new ones are no longer available). Those folks who thought the 'cracks' on the old stem were chisel marks (they were not) will be pleased to hear the new stem has plenty! But beggars can't be choosers and I was lucky to get this stem! The new dust seal, which sits under the cup, wouldn't fit due to a number of small 'lips' made by the chisel indents. After some careful work with a fine file, emery cloth, fine wet&dry and Solvol, the stem is now as smooth as a secondhand car salesman.
The cup will be fitted using the old cup as a drift, complete with a piece of steel tube over the stem. The races will be cooled in my freezer and fitted with a drift I've made reducing 50mm round steel bar to 46.8mm, to snugly fit in the 47mm race recess.
Photos of the stem as received and as cleaned-up

Hi Mark. I presume it’s all up and running by now. Were you able to progress the research on the old stem? Very interesting thread, it deserves a good answer.