Don Terrill’s Speed-Talk

Digger,
No not one big bearing. Each has it's own oil supply; & same oil pressure. So the oil trying to exit the trapped rod is stopped/slowed down by the oil from the 'free' rod.

Gday
What engine, what crank, what cylinder?
Sorry to see carnage!
Cheers
Paul

The photo clearly shows a fatigue break. That's the easy part. Now why there was a fatigue break is the real question.

1. A rod bearing failure could have caused excess loading, but it typically still takes quite a few cycles to get the rod bolt to break when the loading is above the knee. (The knee is the point on the fatigue failure cycles chart where the number of cycles becomes irrelevant as the member is strong enough to survive forever at that cyclical loading level.)

2. The rod bolt had a flaw that allowed a stress riser and started a fatigue crack. The crack started at the outer most edge of the bolt probably in the neck down area. My best guess is that the machining process wasn't smoothed up enough with the surface finishing process.

3. The rod bolt wasn't torqued high enough to maintain the clamp loading of the assembly. This allowed cyclical loading to impact the bolt.

My best guess is that numbers 2 and 3 are to blame either separately or combined.

Did you have stretch measurements on the bolts at rebuild?

The rod and bearing are burnt black from loss of hydrodynamic oil wedge. End of story

Now if the rod bearing was starved for oil wouldn’t both of them have failed.Just asking

Gday,
Vey common on some engines to fail just one rod bearing of a pair from lack of oil or an oil system issue.
What type of engine and what number is the failed cylinder ?
Cheers

#7 rod on 351cleveland

1972ho wrote: ↑Thu Oct 12, 2017 6:18 pm Now if the rod bearing was starved for oil wouldn’t both of them have failed.Just asking

No , of course not.

They're fed from different main bearings.

2, 3 and 4 mains on a cleveland feed two rods each.
Cheers

Any chance this crank rod journal can be repaired and can you see a way to get the #3 rod bolt to loosen.

In the case of a Cleveland......numbered 1234 down one side and 5678 down the other
Then no 7 (spun )pairs with no 3 on the same throw.
No 3 big end feeds from no 3 main and no 7 big end feeds from no 4 main.
If there's going to be a problem with another bearing due to the main not feeding properly then it will be no 4 big end as that also gets oil from no 4 main.
Still separate oil feeds though.

Anybody know if a windage tray can have a effect on the oil system,the reason I ask this is that is the only change that I made to this engine in the many years that I have ran it.I know one thing I will more than likely not install it on the rebuild.

Gday ,
As i aked earlier, is it a standard ford crank?
Cheers

Tuffxf yes 4MA cleveland crank 3.513 stroked.

Gday,
Yeah ok are you also using half grooved main bearings?
How is the bottom end set up clearance and oiling system wise ?
Flatty or roller?
Lifter bushes?
What type of lifters?
Cheers