Anyone Ever See a Rod Cracked Like this Before?

[jluetjen]

Zindt at Lindskog Balancing over in Boxborough MA has been balancing the rotating and reciprocating parts for my 911 race engine project (Carb'd, High-CR, 2.2 liter with full race cams), and spotted this crack on one of the rods. (Note that I've traced the general shape of the crack below the rod, the crack is between the two red arrows.)



We both thought that it was a curious place and direction for a crack to form, and he suggested that it may be a remnant of the forging process where some of the material got folded over during the forging process. As such it may have existed in the rod since the day it was made. Zindt ground away a significant amount of material and the crack went fairly deep. Needless to say I've now got another paper weight and need to get a replacement rod(s). Aside from the balancing service, his sharp eye (and sensitive fingers) have already justified the investment in sending the parts to him.

- Anyone ever see something like this before?
- Anyone got some 2.2 rods collecting dust that they'd like to make a deal on?

[304065]

I've never seen or heard of anything like it. Lucky you found it.

Do you need a whole set of rods? I bet Tom Butler has a used 2,2 rod that is probably close to the weight you need.

Also, the small end looks like it's been ground. Was that done to balance end-for end? Or is it the factory cleanup, just made to look brighter by the camera?

[Grady Clay]

John,

Yes, I have seen that. This is the reason I tested every rod; Zyglow, X-ray, Magnaflux and more. When a rod is under severe stress, there isn’t a test that isn’t worthwhile.

For my personal race engines, I sorted way over 100 rods to find the best. Every customer rod was inspected. 30 years ago we provided the X-rays to our customers. The best shops do that today.

A crack in a connecting rod is a serious issue. It is very uncommon with Porsche rods. Nevertheless, it is still something every engine builder is concerned about.

Best,
Grady

[jluetjen]

Originally posted by john_cramer

Also, the small end looks like it's been ground. Was that done to balance end-for end? Or is it the factory cleanup, just made to look brighter by the camera?

Yes John. The small end was ground down for balance. The finished rods are shot-peened anywhere where they were ground. I'm going to have the 11 remaining (5 which have been balanced and the 6 that I just bought) magnefluxed, and I'll post any anomolies that we find.

[JeffreyNMemphis]

I tweaked your photo...

[chris_seven]

I would worry about locally shot peening rods.

The residual stresses that are produced by shot peening could cause deformation of the rod.

I think it would be better to peen the entire rod and blank off the big end side faces using a nylon coated steel plate.

I would also assemble the rod with reduced head bolts so that the region below the bolt head can be peened as well.