Aaagghhh! Camshaft broke

[stevef]

Had to share this, I couldn't believe my eyes when I saw what happened. I was doing my sprocket alignment measurement on my 2.2 I'm rebuilding. Just retorqueing the left side camshaft nut. Had the wrench set to 120ftlbs (not even the 150). Everything suddenly goes bang!. I look down thinking I had fallen off the nut with the crowsfoot. Took me a while to realize that the whole end of the shaft had sheared at the root of the threads. I just could not believe it. Took me a while to process what I was seeing. Anybody ever had that happen or seen it before?

[RoninLB]

Never seen or heard of that happening

[cstreit]

I've seen them break in shipping, but not like this. You are probably quite lucky that it happened now, instead of later when your engine was together. Any area that is swedged down like the early camshafts is subject to stress risers in that area... ..for the same reason that torsion bars larger thatn 33mm tend to crack.

I would get a replacement one, then have them both magnafluxed...

[Doug Zielke]

Steve.....*please* be so kind as to post some pictures. TIA

[stevef]

Doug, I'll do that. I'll take some tomorrow and post them.

[RoninLB]

not for nothing; but,

I'd love to read what Jim Sims says about this ?

[Wayne 962]

Not common, but I have seen at least one broken one before..

-Wayne

[stevef]

This is the first time I've attached a pic. Hope it works. Here are the two pieces of the shaft after I removed it from the housing. I can't tell where the break originated. As you said Chris, good job it happened now.

[jgparker]

Wow, that picture is incredible. I didn't think they could break that way. Let me know if you need a core to regrind.

JP

[snowman]

SUPERGLUE

[stevef]

Snowman.......thick or thin ?...superglue that is.

[Ho Hum 74]

Looks like the shaft might have had a crack on the right side of the left shaft in the pic (unless that's the start of the threads). Strange that the two halves are flat. Most shafts that fail in torsion fail at about a 45 degree angle to the length of the shaft.Sorry to hear about that.

Tristan

[RoninLB]

maybe the cam was dropped on the ground that set up a stress riser ?

[cstreit]

Yep Tristan I agree, looks like a crack started on that upper right

[Doug Zielke]

Thanks for the image, Steve!

[MotoSook]

There it is....where it started.



It is "tensional" failure (perhaps the the technical term I should use, but it's late and it's been years since I was in a lab)...the surface is not unlike what I have seen when I have performed such failure in the lab.

[stevef]

Souk, I assume you are refering to the little tear on the r.h.s. I figured something was happening there.

[MotoSook]

Well, nothing is conclusive until I have the part in hand (and then maybe), but my first analysis seems to be backwards. The fracture ("stress fracture") likely started in the 6-7 o'clock position in the picture I editied. The area I circled is the final fracture area (shear lip). The two features in the middle look suspiciously like a couple of inclusions that would have added to the weakening of the part. The 6-7 O'clock position (area) looks like there may be radial marks that would indicate it started there. But the crack didn't start in the middle or there would be some coning/cupping effect.

Were the camshafts cased then machined? Or were they forged..did they forge them back then?

If the casting had an inclusing that was machining into, it is likely that this part was destined to fail at that spot. The crack doesn't look a fatigue failure, so that part was probably bummed from the start. It just failed....

You ARE luck it happened during assembly.

[stevef]

I'm not aware of the history of the part. It came out of the same motor originally. It was a runner and there didn't appear to be anything amiss with the shaft. If you are interested this part is no good to me. I could get the boss cut off the shaft and send you the 2 bits.

[MotoSook]

Steve, I wish I had time to play with such things, but thank you for offering.

I'm sure it wasn't anything you did to cause it to fail, so my best guess is that it was just its time....