The pinch bolts would never get tight enough to break the leg like that… especially on two different legs. Manufacturing errors.
Yes, I noticed a crack in the second fork when I started to tighten everything down. Both forks cracked in the same way.
Are those M6 or M8 bolts? Had a guy come to our shop a long time ago who broke two triple clamps because he was using a miscalibrated torque wrench. Also, are you torqueing them all at once, or alternating and working up to the torque value? I'm a torqueaholic, but axle pinch bolts are one of the few bolts I'm ok with elbow-clicking. There is a lot of surface area there, you don't need to go aggro on those.
M8. Definitely wasn't going ham with the ratchet. I was going back and forth when I noticed the second fork cracked. Here is a picture of the second fork.
That last picture almost looks like the crack starts on the inside, like the axle is too big in diameter, and expanding everything outward.
I've had alot of bikes thru the shop over the years doing front tires where the pinch bolts were stupid over tight from the previous guy and have never seen one cracked.
From looking at the last picture I am going with an axle issue. It appears that the crack originated from inside to outside, which could have been from tightening the pinch bolt but when looking at the axle the hex appears to be off-center from the axle. I would start looking at the concentric of the axle and the fork.
I agree.. that crack started on the inside, if the bolt created the crack it would start on the outside.
Did you use the same M8 cap screws for both forks? Also, any lockwashers or flat washers underneath the bolt heads? Do you have pics of the hardware?
The off-center look is created by the shadow. Also, I'm not convinced the the crack would start from the outside if the bolt caused it. The thinnest cross section can result from the OD of the counterbore for the bolt head being pretty close to the axle bore: The reason I asked about the hardware is because a lockwasher will dig into the aluminum and could cause a stress riser. and possibly the cap screw with the wrong head shape could be an issue.
I totally understand what you are saying and it is hard to pinpoint the issue but with that said my rationale is that the common denominator is the axle and pinch bolts as you have cracked two "different" fork legs using the same axle and bolts.
Not really clear on this but the second fork may well have been cracked before he bought it. Time for a new set of Ohlins!