Calling mech eng - con rod failure mode?
Discussion
Following on from when
came out of
I know it had oil in it at the time, but I'd not had the car very long so I don't know the history before. But I've been looking at the rod and wondering. On one side, the cap bolt is still in place:
and it's failed at the join to the cap:
On the other side, the bolt is missing, along with some of the thread
The thread at the top is quite good, the next section is damaged, the next section you can see the marks but only because of how the torch light is, the last section towards the join is practically smooth.
So I'm wondering, did that bolt start to come loose and then tear out in stages, causing the failure?
Or am I looking too hard for reasons and simply bought a car that was already a ticking bomb due to earlier abuse (as well as being an Alfa
)?
Thanks in advance folks....
came out of
I know it had oil in it at the time, but I'd not had the car very long so I don't know the history before. But I've been looking at the rod and wondering. On one side, the cap bolt is still in place:
and it's failed at the join to the cap:
On the other side, the bolt is missing, along with some of the thread
The thread at the top is quite good, the next section is damaged, the next section you can see the marks but only because of how the torch light is, the last section towards the join is practically smooth.
So I'm wondering, did that bolt start to come loose and then tear out in stages, causing the failure?
Or am I looking too hard for reasons and simply bought a car that was already a ticking bomb due to earlier abuse (as well as being an Alfa
)?Thanks in advance folks....
eldar said:
Could be any number of things. Blocked oilway to the big end, partially seized piston, pre ignition or badly assembled for example.
Hard to tell from the pictures, which are probably effect rather than cause. Need to get all forensic on the remaining bits.
Remaining bits are either scattered over the road it blew on or with the bloke who bought it off ebay (and is fitting a new engine Hard to tell from the pictures, which are probably effect rather than cause. Need to get all forensic on the remaining bits.
).But if the feeling is effect rather than cause, I'll stop worrying about how I got my new paperweight!
The rods is black so it's an oiling problem.
Probably this scenario...Bearing starves of oil for whaever reason,bearing starts to spin,rod overheats,rod bolts weaken and come loose,one rod bolt comes out completely,the other rod bolt starts to fracture,cap starts hitting the inside of the block,cap hits the block hard enough to break the bolt completely,cap comes off,rod goes on a walkabout,engine expires..
Probably this scenario...Bearing starves of oil for whaever reason,bearing starts to spin,rod overheats,rod bolts weaken and come loose,one rod bolt comes out completely,the other rod bolt starts to fracture,cap starts hitting the inside of the block,cap hits the block hard enough to break the bolt completely,cap comes off,rod goes on a walkabout,engine expires..
redvictor said:
The rods is black so it's an oiling problem.
Probably this scenario...Bearing starves of oil for whaever reason,bearing starts to spin,rod overheats,rod bolts weaken and come loose,one rod bolt comes out completely,the other rod bolt starts to fracture,cap starts hitting the inside of the block,cap hits the block hard enough to break the bolt completely,cap comes off,rod goes on a walkabout,engine expires..
Yup, most likely. But the mystery is what was the oiling problemProbably this scenario...Bearing starves of oil for whaever reason,bearing starts to spin,rod overheats,rod bolts weaken and come loose,one rod bolt comes out completely,the other rod bolt starts to fracture,cap starts hitting the inside of the block,cap hits the block hard enough to break the bolt completely,cap comes off,rod goes on a walkabout,engine expires..
The half bolt that's still in the rod looks like a possible fatigue fracture, the clean looking break on the right side as pictured could have been slowly building over time until reaching the critical point where it all went bang, possible due to bolt damage, material fault or something else giving an initial weakness where the crack could start.
Of course that's still very speculative and without very detailed pictures its hard to say, and like others have already said it could just be the effect of a failure that started somewhere else.
Other than that it just looks pretty nasty, good luck with getting it fixed!
Of course that's still very speculative and without very detailed pictures its hard to say, and like others have already said it could just be the effect of a failure that started somewhere else.
Other than that it just looks pretty nasty, good luck with getting it fixed!
Boosted LS1 said:
Andy, in what way is the rod black? I've seen lots of rods looking like that.
OP where are the shells and what do they look like? They would show any oiling issues.
Rod bolt failure is quite a common cause for rod failure.
First pic where the bearing used to be.It's as black as your hat..OP where are the shells and what do they look like? They would show any oiling issues.
Rod bolt failure is quite a common cause for rod failure.
Rod bolts almost always don't just fail on their own. There's always a factor for failure.Overheating/not enough stretch/too much stretch.Oil starvation is one of the biggest factors.
Edited by redvictor on Friday 20th August 23:30
It's f
ked, is that. Proper.redvictor said:
Boosted LS1 said:
Andy, in what way is the rod black? I've seen lots of rods looking like that.
OP where are the shells and what do they look like? They would show any oiling issues.
Rod bolt failure is quite a common cause for rod failure.
First pic where the bearing used to be.It's as black as your hat..OP where are the shells and what do they look like? They would show any oiling issues.
Rod bolt failure is quite a common cause for rod failure.
Rod bolts almost always don't just fail on their own. There's always a factor for failure.Overheating/not enough stretch/too much stretch.Oil starvation is one of the biggest factors.
Edited by redvictor on Friday 20th August 23:30
ADEuk said:
No, bit of a design boo boo. The exhaust downpipe runs through a channel in the sump so when switching off the engine, No 3 big end ends up sitting very close to it. Cheap oil will bake off leaving it dry for the next start up. After the years this takes it's toll
It always (I say always, for the 6 months I had it!) a bit clattery on start up, went after a few seconds..... hmmm....Gassing Station | General Gassing [Archive] | Top of Page | What's New | My Stuff