Cracked FR Fork leg ??? !!!

[kfrogzx7]

https://photos.app.goo.gl/VGuVDrVd3kFmhQL38

Sorry it's a link, not a picture ... I can't add it as an image.

Did a track day at Snetterton today and after a couple of sessions ( rained off after that anyway ) I spotted this crack on the ally base of my right fork
Has anybody seen anything llike it before ?
It doesn't look that new but then again I've only used my 11s for trackdays for about 5 years now.
Any ideas what could have caused it and suggestions about whether it's safe to use like that ( I know it's not !!! ) ?
I'm wondering whether water ingress between the steel leg and the ally fork bottom has cause corrosion inside leading to weakness under repeated track day type heavy braking ?

[kfrogzx7]

PS It's never been down the road or anything like that.

[Blackal]

I suspect it may be corrosion that will have caused that. On two fronts..............

Metal oxide occupies a much larger volume than the parent metal (steel is 7 times greater volume)

Corrosion can cause interstices which make cracking more likely.

The alloy corrodes and swells - and cracks to relieve the stress.

You're gonna need a new bottom unit, but I'd suggest dismantling/inspection to establish the extent before looking for new bits.

[kfrogzx7]

I suspect it may be corrosion that will have caused that. On two fronts..............

Metal oxide occupies a much larger volume than the parent metal (steel is 7 times greater volume)

Corrosion can cause interstices which make cracking more likely.

The alloy corrodes and swells - and cracks to relieve the stress.

You're gonna need a new bottom unit, but I'd suggest dismantling/inspection to establish the extent before looking for new bits.

How far can you dismantle, you can't separate the steel fork tube from the ally casting can you ? I don't even know how they are attached ... threaded ? interferance fit ?
Have you seen anything like it before, if it's just down to corrosion surely it'd be more common ? And if hidden corrosion can just suddenly cause a fork failure surely it's a big safety issue ?

[jeznewsome]

Do you Brembo or BMW marked calipers. If it is the former then I have a pair of lowers you can have for postage.

[Blackal]

I suspect it may be corrosion that will have caused that. On two fronts..............

Metal oxide occupies a much larger volume than the parent metal (steel is 7 times greater volume)

Corrosion can cause interstices which make cracking more likely.

The alloy corrodes and swells - and cracks to relieve the stress.

You're gonna need a new bottom unit, but I'd suggest dismantling/inspection to establish the extent before looking for new bits.

How far can you dismantle, you can't separate the steel fork tube from the ally casting can you ? I don't even know how they are attached ... threaded ? interferance fit ?
Have you seen anything like it before, if it's just down to corrosion surely it'd be more common ? And if hidden corrosion can just suddenly cause a fork failure surely it's a big safety issue ?

Ah - no it doesn’t dismantle further. I imagine that there is some insulation between the different metals (against galvanic action) which in your instance - has broken down?

I’m still going for corrosion as opposed to mechanical failure.

[RiceBurner]

I suspect it may be corrosion that will have caused that. On two fronts..............

Metal oxide occupies a much larger volume than the parent metal (steel is 7 times greater volume)

Corrosion can cause interstices which make cracking more likely.

The alloy corrodes and swells - and cracks to relieve the stress.

You're gonna need a new bottom unit, but I'd suggest dismantling/inspection to establish the extent before looking for new bits.

How far can you dismantle, you can't separate the steel fork tube from the ally casting can you ? I don't even know how they are attached ... threaded ? interferance fit ?
Have you seen anything like it before, if it's just down to corrosion surely it'd be more common ? And if hidden corrosion can just suddenly cause a fork failure surely it's a big safety issue ?

Ah - no it doesn’t dismantle further. I imagine that there is some insulation between the different metals (against galvanic action) which in your instance - has broken down?

I’m still going for corrosion as opposed to mechanical failure.

I was under the impression that they're screwed together - with a very fine thread. I'm sure I've seen write ups where someone has managed to unscrew the the lower from the tube.

[kfrogzx7]

I was under the impression that they're screwed together - with a very fine thread. I'm sure I've seen write ups where someone has managed to unscrew the the lower from the tube.

Yes, I must admit I had a vague idea that they were screwed togther too ?

[kfrogzx7]

Do you Brembo or BMW marked calipers. If it is the former then I have a pair of lowers you can have for postage.

Thanks for the kind offer Jez, but mine are BMW. I've bought a 2rd hd replacement already anyway ( next track day is looming ), thanks.

[Blackal]

Yes, I must admit I had a vague idea that they were screwed togther too ?

I had gone looking for google images, thinking the same - but could find no reference.

If it has, then it should be a pretty short thread at the end - the thread section would need to have no chance of 'flexing' in service.

[dave the german]

If you go back far enough, there was a Trixter that did remove the lower part and replace it with some parts from Italy so he could mount radial brakes. Is there a small grub screw on the inside of the fork leg? that would seem to be the giveaway. It may only be certain parts it affects and others are an interference fit

[dave the german]

BMW part site lists 2 forks - I think the fork bottom that has the grub screw may be off the 04 BCR. I seem to recall the guy who replaced the fork bottoms had to get the anodising re done because of colour fading

[nab 301]

I found this old thread on removing the caliper mounts
viewtopic.php?f=4&t=19809&hilit=front+caliper+mount&start=30

[dave the german]

That's the thread I was on about Nigel. Stunning job

[boxerscott]

What Blackal sed, corrosion jacking. My money`s on that. Seen that lots of times on cast pipework spigot and socket joints.

Chris