Broken rod bolt

General engine tech -- Drag Racing to Circle Track

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DaveMcLain
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Re: Broken rod bolt

Post by DaveMcLain » Wed Oct 04, 2017 7:53 pm

You might want to look at the block really closely and see if it might have cracked in the main webbing, starved for oil and cooked the rod bearing. I had a circle track customer one time who blew out an intake gasket on his Chevy while racing. It filled the case with coolant and spun a bearing quite quickly without overheating. All kinds of weird stuff can happen to a previously good engine.
Last edited by DaveMcLain on Wed Oct 04, 2017 7:55 pm, edited 1 time in total.

340king
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Re: Broken rod bolt

Post by 340king » Wed Oct 04, 2017 7:55 pm

It might be informational to see the surface of the bolt that broke. That way we might be able to determine whether it was a ductile fracture or a fatigue break. More than likely if it was a spun bearing we will see a fully grained surface across the broken bolt. If it was a fatigue failure, then we should see come clam shell marks across the broken face. It would be a clue, but might not end the discussion on which came first.

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Re: Broken rod bolt

Post by Cubic_Cleveland » Wed Oct 04, 2017 8:06 pm

statsystems wrote:
Wed Oct 04, 2017 7:50 pm
Cubic_Cleveland wrote:
Wed Oct 04, 2017 7:45 pm
Too add to the spun bearing theory, this is a Toyota 5L rod that broke a bolt. Zero heat discolouration..
IMG_3190.jpg
Did the bolt fail first or did the rod break?
Bolt broke. They are recommended to be one use only, and Toyota have a spec to measure against. Obviously the shop who rebuilt it decided to skip the $80 insurance policy :lol:

joe 90
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Re: Broken rod bolt

Post by joe 90 » Wed Oct 04, 2017 9:01 pm

It's quite common for the Toyota 5L to break rod bolts.
If any Toyota L series spins a big end bearing, it's always no 4 for some reason?
Probably because it's furthest away from the pump.


Waiting for pics of the big end bearings to appear?

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Re: Broken rod bolt

Post by jsgarage » Thu Oct 05, 2017 3:12 am

There's several ways for too-heavy oil to fail an engine,guys. I blew a screw-on oil filter clean off the block at 6500 rpms with 50-wt & a high volume oil pump. I was not the most popular driver at that event. It didn't quite empty a 10-quart oil pan before I got it shut down. Fram went thru a time where their filters were made in the far east somewhere. Track cleanup took almost an hour. No engine damage but people still remind me of that one. Lesson learned.

Geoff2
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Re: Broken rod bolt

Post by Geoff2 » Thu Oct 05, 2017 4:29 am

The Toyota 5L rod shown has heat discolouration at the 12 o'clock position.

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Re: Broken rod bolt

Post by Geoff2 » Thu Oct 05, 2017 4:39 am

So what happens under this scenario, on a V8 with * inexplicable* rod failure: one rod gets trapped up against the crank cheek by the other rod; could be many reasons for this; bore not perpendicular; bent rod; uneven combustion; etc. So how does the oil under the trapped rod, exit the journal & allow fresh, cooler oil to enter the bearing space? Is this why random rod brg failures occur? Food for thought.
For 30 yrs I have ground three shallow recessess on the crank cheek side of the rod to allow oil to escape, should the above scenario occur.

If the engine in question is a Pontiac [ 455HO ], they have p*ssy little 3/16" feed holes in the main brg shells. I elongate the holes, along the bearing groove.

digger
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Re: Broken rod bolt

Post by digger » Thu Oct 05, 2017 5:20 am

it goes out the other side of the rod that is squishing it against the crank as they act connected as one big bearing

mag2555
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Re: Broken rod bolt

Post by mag2555 » Thu Oct 05, 2017 6:42 am

When a Rods big end starts to get distorted even by only .001" ) by excess loads or by the bolts starting to go south then the first thing that takes place before any beginning of a audible knock starts is the bearing shifts at the parting line and scrape the oil right off the journal instead of riding on the oil film.

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Re: Broken rod bolt

Post by Cubic_Cleveland » Thu Oct 05, 2017 7:43 am

Geoff2 wrote:
Thu Oct 05, 2017 4:29 am
The Toyota 5L rod shown has heat discolouration at the 12 o'clock position.
No, it doesn't. My guess is it's a product of my poor photography more than anything else :oops:

1972ho
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Re: Broken rod bolt

Post by 1972ho » Thu Oct 05, 2017 1:39 pm

Pic of broken rod bolt
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Re: Broken rod bolt

Post by Frankshaft » Thu Oct 05, 2017 2:24 pm

Yes, it got slide hammered until it broke. Once the bearing is gone,the space that is there, from the mission bearing, each time the rod comes around both ways, it gets slide hammered, until it finally breaks. That's what happened. You lost the bearing first.

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Re: Broken rod bolt

Post by sanfordandson » Thu Oct 05, 2017 2:32 pm

Any time ive seen the bolt as the failure you never see discoloration. Blue or black is a bearing or oil issue.

1972ho
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Re: Broken rod bolt

Post by 1972ho » Thu Oct 05, 2017 3:27 pm

I just never heard any rod knocking last time I had a rod/bearing fail I heard the rod knocking around and was able to save it and when I pulled the pan the bearing was smashed down to a shim,but the nothing else was damaged.

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Re: Broken rod bolt

Post by joe 90 » Thu Oct 05, 2017 7:31 pm

How about some pictures of the crank?

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