Broken rod bolt

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Geoff2
Expert
Expert
Posts: 633
Joined: Mon Nov 09, 2015 4:36 pm
Location: Australia

Re: Broken rod bolt

Post by Geoff2 » Fri Oct 06, 2017 4:27 am

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.

tuffxf
Member
Member
Posts: 181
Joined: Wed Dec 20, 2006 7:34 am
Location: Central Qld Australia

Re: Broken rod bolt

Post by tuffxf » Fri Oct 06, 2017 6:56 am

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

340king
Expert
Expert
Posts: 568
Joined: Tue Mar 11, 2008 8:43 pm
Location: Fort Pierre, SD

Re: Broken rod bolt

Post by 340king » Sat Oct 07, 2017 11:30 pm

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?

MELWAY
Expert
Expert
Posts: 754
Joined: Mon Dec 04, 2006 7:37 pm
Location: melbourne australia

Re: Broken rod bolt

Post by MELWAY » Sun Oct 08, 2017 7:53 am

The rod and bearing are burnt black from loss of hydrodynamic oil wedge. End of story
3370lb Sedan 9.89@136MPH 358chevN/A

1972ho
Expert
Expert
Posts: 500
Joined: Thu Nov 21, 2013 12:52 am

Re: Broken rod bolt

Post by 1972ho » 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
You do not have the required permissions to view the files attached to this post.

tuffxf
Member
Member
Posts: 181
Joined: Wed Dec 20, 2006 7:34 am
Location: Central Qld Australia

Re: Broken rod bolt

Post by tuffxf » Thu Oct 12, 2017 6:27 pm

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

1972ho
Expert
Expert
Posts: 500
Joined: Thu Nov 21, 2013 12:52 am

Re: Broken rod bolt

Post by 1972ho » Thu Oct 12, 2017 7:39 pm

#7 rod on 351cleveland

joe 90
Guru
Guru
Posts: 2072
Joined: Tue May 27, 2014 4:02 am
Location: The land of the long white cloud

Re: Broken rod bolt

Post by joe 90 » Thu Oct 12, 2017 8:15 pm

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.

tuffxf
Member
Member
Posts: 181
Joined: Wed Dec 20, 2006 7:34 am
Location: Central Qld Australia

Re: Broken rod bolt

Post by tuffxf » Thu Oct 12, 2017 8:21 pm

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

1972ho
Expert
Expert
Posts: 500
Joined: Thu Nov 21, 2013 12:52 am

Re: Broken rod bolt

Post by 1972ho » Thu Oct 12, 2017 8:43 pm

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

joe 90
Guru
Guru
Posts: 2072
Joined: Tue May 27, 2014 4:02 am
Location: The land of the long white cloud

Re: Broken rod bolt

Post by joe 90 » Thu Oct 12, 2017 10:21 pm

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.

1972ho
Expert
Expert
Posts: 500
Joined: Thu Nov 21, 2013 12:52 am

Re: Broken rod bolt

Post by 1972ho » Thu Oct 12, 2017 11:46 pm

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.

tuffxf
Member
Member
Posts: 181
Joined: Wed Dec 20, 2006 7:34 am
Location: Central Qld Australia

Re: Broken rod bolt

Post by tuffxf » Fri Oct 13, 2017 12:23 am

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

1972ho
Expert
Expert
Posts: 500
Joined: Thu Nov 21, 2013 12:52 am

Re: Broken rod bolt

Post by 1972ho » Fri Oct 13, 2017 9:48 am

Tuffxf yes 4MA cleveland crank 3.513 stroked.

tuffxf
Member
Member
Posts: 181
Joined: Wed Dec 20, 2006 7:34 am
Location: Central Qld Australia

Re: Broken rod bolt

Post by tuffxf » Fri Oct 13, 2017 11:18 am

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

Post Reply