How did this happen?

[Pozzy]

Pulling away from a junction last October, at about 2.5-3k rpm there was a bang/thump followed by a tinkling of metal (never a good sign!).

I've finally got round to whipping the inlet manifold off to be greeted with this beauty:



A couple of shots from underneath:




Pretty comprehensive damage! I'm hoping to have a new engine put in in the near future, but upon looking at this yesterday a mechanically-minded friend of mine is utterly convinced that this was caused by the camshaft letting go:



It's certainly quite neatly sheared. The camshaft was only installed 6 months/6000 miles before the engine lunched itself, so I'm not sure whether that's likely?

For clarification, the conrod appears to have been "stretched" apart, as opposed to the shear seen on the camshaft.

People's thoughts/opinions would be most welcome about this, because obviously if it's the fault of the camshaft I may have some recourse with the manufacturer rather than having to pay for the whole engine out of my own pocket!

Edited by Pozzy on Sunday 19th May 15:42

[Silent1]

Good old thumbsnap not showing photos as per usual!

[Pozzy]

Argh, I can see them on my side! Would it help if I changed them to thumbnails?

[Silent1]

Pozzy said:

Argh, I can see them on my side! Would it help if I changed them to thumbnails?

nope, thumbsnap is notorious, you're best to try something like http://tinypic.com/

[Pozzy]

Silent1 said:

nope, thumbsnap is notorious, you're best to try something like http://tinypic.com/

Thanks, should work now!

[Silent1]

Perfect, i can see them now, i wouldn't like to voice an opinion as i wouldn't call myself qualified in the failure mechanics of engines but the conrod being a tension failure sounds very odd to me as wouldn't something have to have held it to cause that.

[Mr2Mike]

The other way around is far more likely i.e. the snapped con rod has sheared the camshaft and smashed the casting around the lifters.

Why the con rod snapped is the question. Possibly it was damaged in the past e.g. bent after ingesting water, and happened to run out of fatigue life at that point.

[stevieturbo]

As above, it'll be the conrod breaking that caused the other damage.

[Evoluzione]

Have you got a pic of the big end bearings on that broken rod?

[Steve_D]

Is the remainder of the conrod still attached to the piston?
Does the piston move?

I don't believe the cam was the failure mode.
I'm leaning towards the piston seizing and breaking the rod.

Steve

[tvrolet]

Been there, done that...allbeit on a Small Block Chevy (in the Tuscan). First of 3 engine blow-ups

Only real difference was that on mine it was the rod on number 1 that snapped and punched through the cam, and with the rest of the cam stopped for 2 through 8 cue further pistons hitting valves.

In my case the root cause was that it had spun a big-end bearing. I actually heard a 'ticking' before it went, but thought it was one of the lifters not pumping up. With the extra play and a bit more friction not all the forces went straight down the rod - it introduced a slight bending effect under load from the piston and hey presto one snapped rod. I'd hazard a guess that the big end of the snapped rod isn't silky-smooth if you move it on the crank.

[GavinPearson]

It's probably pre-ignition that caused the piston to let go, in turn failing the rod, which then took everything in it's path out.

Low speed pre-ignition can be quite damaging. Look at the plug heat range and deposits on the other plugs for clues to the PI events.