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BBCMudbogger 07-23-2008 02:36 PM

Rod bolt failure
 
Anybody here have any rod bolt failures? I know a guy that lost a rod bolt last weekend ARP wav-locs in a big chevy the bolt failed at idle.

killerformula 07-23-2008 02:48 PM

how many miles on this motor?

BBCMudbogger 07-23-2008 02:51 PM

Its a race engine w/ probably 60 200' passes on it (mud racing)

Double_v23 07-23-2008 03:01 PM

What motor? The cap probably walked if it was a stroked BBC.

oldbogie 07-23-2008 04:24 PM

Quote:

Originally Posted by BBCMudbogger
Anybody here have any rod bolt failures? I know a guy that lost a rod bolt last weekend ARP wav-locs in a big chevy the bolt failed at idle.

The bolt was already failed, it just came apart at idle.

You need to look carefully at the bolt and the cap. Bolts fail for lots of reasons but the most common is in bending. If the cap was walking around under load it puts a bending stress on the bolt. The bolt in the failure zone will have rows of shiny ridges followed by an abrupt tear. The flat mating parts of the cap and rod will have places where the material look dull and perhaps scared.

A bolt that's just ripped apart with a jagged tear probably backed off, look for again for dull marks and or scaring in the cap to shank interface and also under the bolt head to cap. This would also indicate the cap is squirming around and caused a loss of clamping force which then allowed the bolt to back out a little to where it got hammered on till it broke. This is mist likely a failure under the head where the previous failure is more likely in the shank close to where the thread start. Though a bolt that lost its clamping force might also fail in the shank, but it will most likely be a sudden rupture.

This is also more common to rods that have the big end resized as this tends to bend the bolts as they're torqued up. It's also common in aluminum rods that have been run too many passes.



Bogie

k-star 07-24-2008 05:45 AM

bolt
 
I would want to know the detailed assembly procedure before i blamed the bolt, not that there can't be material issues with bolts but it's not very common.

What was the free length of the bolt out of the box. what was the bolt stretched to during assembly, and re-sizing,did the bolt retain it's orginal length with-in .001 after the first stretch.

If the engine was assembled only using a torque wrench and not a stretch gage it's all over, the bolt was not the issue...

Keith

woodz428 07-24-2008 07:55 AM

I agree that bolt failure like that is pretty rare, especially for a good quality one. I almost always have to consider the assembly/assembler of the engine. The only time I've seen a bolt fail under those conditions was that it never was torqued properly, just from examining other engines. Many times people like to snug down the nuts prior to torqueing and under some conditions, long hours/frenzied pace, it is not uncommon to miss a nut when dooing final torqueing. I have seen it enough that I always double check if I don't recall doing a specific step. Late nights can cause many things that are operator error and not material, although it is usually the material that gets the blame....it can't argue.

BBCMudbogger 07-24-2008 08:13 AM

Interesting. I can say I know it was installed with a strecth gauge by a top notch builder who has plenty of racing engines out there.

k-star 07-24-2008 08:32 AM

bolt
 
Not tying to be stupid, just playing the bad guy..

I have been in some top notch builders shops and seen what they do. I am not saying it happened here, but something to think about..

Some of the bigger well known shops are very busy and they do not have time for a lot of detail work. It takes a long time to stretch each rod bolt. What I have seen happen is they will do one bolt, calculate the required torque and do the other 15 bolts with a torque wrench. I can tell you first hand this does not work…

Next, like was mentioned there is slim chance the bolt got missed, but IMO very unlikely because I would think that would have showed up on the first pass, But stranger things have happened. I mark all my bolts with paint marker as I stretch them that way none get missed…

Another possibility, maybe the bolt came in contact with a chemical that reacted to the base metal, something like brakecleen.

Could be a material failure…

A lot of times in this type of failure the true cause is never found…

BBCMudbogger 07-24-2008 09:56 AM

Yeah "one of those things" I am not trying to find fault more or less for my own info trying to understand what possibilities there are. Keith can you elaborate a tick more on the brakleen deal?

k-star 07-24-2008 10:56 AM

rods
 
Different chemicals can interact with different metals (as well as other metals, putting stainless into aluminum as an example). I just used the brakeclean as an example. I am not real familiar with the wave lock bolts. I personally don-not like them in stock rod applications. But I know that using chlorinated brakeclean on titanium is a big problem. There is a chemical reaction that hurts the structural properties of the titanium. So maybe another chemical that reacts to the wave lock bolts came in contact with them..

This was just a “thinking about it” deal. I am not saying that is what happened…

Keith

ScoTFrenzel 07-24-2008 11:20 AM

Quote:

Originally Posted by k-star
I have been in some top notch builders shops and seen what they do. I am not saying it happened here, but something to think about..

Some of the bigger well known shops are very busy and they do not have time for a lot of detail work. It takes a long time to stretch each rod bolt. What I have seen happen is they will do one bolt, calculate the required torque and do the other 15 bolts with a torque wrench. I can tell you first hand this does not work…


A lot of times in this type of failure the true cause is never found


Absolutely Keith is right.
I've seen it too, in some pretty substantial race shops.

One thing I learned on my own is that ARP stretch is usually about 25% more torque than what ARP specifies. That convinced me that stretch is the only way to tighten a rod bolt for true high performance useage.

machine shop tom 07-24-2008 05:54 PM

Quote:

Originally Posted by ScoTFrenzel
Absolutely Keith is right.
I've seen it too, in some pretty substantial race shops.

One thing I learned on my own is that ARP stretch is usually about 25% more torque than what ARP specifies. That convinced me that stretch is the only way to tighten a rod bolt for true high performance useage.

Any ARP fastener that is rusty should be thrown into trash because the oxidized metal will cause oxygen embrittlement, leading to a broken fastener.

X3 with using stretch method instead of the repeated torquing procedure that ARP lists with their fasteners.

tom

BBCMudbogger 07-25-2008 08:09 AM

Say hypothetically that an engine hung on a stand for maybe 6-8 months after the last time it ran....would rust begin to develop on internal components after that period of time? Would you be talking about a spec of rust or the whole fastener covered?

sam-missle 07-25-2008 10:11 AM

send the bolt to ARP, you may find it is not an ARP, lot of cloning going on out there.

sam-missle


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