danmyersmn

Some time ago I remember reading a thread about a fork that had demonstrated a potential failure point. If I recall correctly it was a specific Trek fork that was subject to failure at the fork crown. The remedy for the issue was the interior of the crown had a finger/arrow that extended down the fork tube to resolve this issue. When I was doing some work on my brakes I noticed the fork crown I am using is very similar to this and I was wondering if this was a one specific fork/year/model issue, or the design in general? Is this a non issue, or something to be concerned about?


Untitled by bisonmn1, on Flickr

cdmurphy

You should be fine. That Trek fork that had so many cracking issues was an Ishiwata product, and only seemed to affect one or two years. I doubt it was entirely due to the shape of the fork crown - lots of perfectly serviceable forks used crowns without reinforcement like yours. It was probably due to a bad batch of fork blades, or even more likely, overzealous heating of the blade/crown during the automated brazing process.

Chombi1 

Wasn't the bad Trek fork crowns also stamped steel instead of cast/forged items?

gugie 

Possibly so, but that wasn't the root cause. There are tons of tons of bikes that used a stamped steel fork crown that didn't have this issue. If indeed the "bad" Ishiwata forks were all stamped steel, that wasn't the cause, just coincidence.

This thread comes up every 6-12 months, it would seem, with the same exact discussion, btw.

Chombi1 

Just wondering that maybe with some stamped steel fork crowns, the shapes might he so complicated that the steel can get work hardened in the stamping and forming process that they end up prone to cracking......

gugie 

Funny, not seeing many pictures of fork crowns cracking...it's usually the fork blades.

Charles Wahl

OP: Is that a Trek? What model? If it is a Trek, did you look up the easily available Trek catalog for this model to see if it had one of the supposedly defective fork crowns, before coming here and posting one photo with nothing else other than your angst?

Chombi1 

Well here's one posted on our forums.....
https://www.bikeforums.net/classic-v...ork-crown.html
Maybe the question is, did the fork blade crack first or did the crown crack first??.....

gugie 

If I could get that fork, I could probably tell you where the crack started. It might take some microscopy, but it's pretty straight forward. Looking at all the pictures, I'd bet that the crack started on the blade and propagated up through the crown. The blade/fork crown interface is a stress riser - it's a good technical reason for thinning lugs out near the edges (it looks really nice too!)

You get strength from two things: material and design. More material is stronger, stronger material is stronger, both obviously. Overheating material can reduce strength. It's been well documented in this forum by people who worked in the industry as framebuilders that the fear is greater than the reality.

It's really a moot point, however. If I'm riding a bike, all I want to know is if the fork is going to hold up beneath me. I was taught that it's a good idea to pull your wheels off and wipe down your bike on a regular basis. Doing so will get your eyes on most or all of your frame and fork so you can check for issues before they become problems. More than once I've found what looked like it could have been a crack - only to find out it was either a scratch in the paint or something that could be cleaned off.