Sheared off rod bolts...bike

[Keith Morganstein]

Best photo of the sheared bolts....He will take a better photo...

It looks as the bolt on the right broke first. It’s shiny from the the two halves rubbing on each other. The other bolt on left has a rough grainy fracture and appears to have a shear lip.

From what I can see in the photo, one bolt failed and that caused the other bolt to break as the cap hinged open. If I had it to look at, or at least good photos with magnification, I could be more certain.

[Dan Timberlake]

Not a lot of "footprint" at the parting line.

Gen 2 Hemis found they needed "more, more, more" to yank around those HEAVY parts at 7000 rpm.

[MadBill]

Maybe the fix in this case is some clever mill work on the undersides of the piston crowns. I'm holding a 25 year old 4.175" NASCAR Ford piston that weighs ~ 375 g. (albeit it's a flat top) and I suspect that was a mandated minimum...

[Truckedup]

Maybe the fix in this case is some clever mill work on the undersides of the piston crowns. I'm holding a 25 year old 4.175" NASCAR Ford piston that weighs ~ 375 g. (albeit it's a flat top) and I suspect that was a mandated minimum...

I have no idea what his pistons weigh, I believe they are JE... The forged pistons I use weigh 255 grams with no rings, the pin is 60 grams..Mine have much lower flat dome with 10.5 compression rather than high boy 12-1 domes used by many others...I also run a very tight quench ...
As I mentioned, these MAP rods have a repuation for solid reliability in these engines and I believe this might be the first rod failure seen ..Or at least the first failure not due to oil starvation and a spun bearing...

[dwilliams]

From the pictures, I'd weigh in with "rod bolt failure."

With that stroke and piston weight, unless he was turning some crazy RPM, I don't see that the bolts would be particularly stressed.

I can present two scenarios:

A) the bolts were unlubricated, poorly lubricated, or otherwise galled on installation, causing the bolts to start to yield from twisting before they reached proper stretch (given an experienced builder, not a likely scenario)

B) the bolts were counterfeit

A few years ago ARP issued a notice that there were counterfeit "ARP" bolts in some import rods; even if you buy bolts in the original packages, those can be counterfeit too. ARP wasn't the first and won't be the last. If the rod company bought bolts from a reseller, counterfeits can enter the supply chain at several points.

If you want to be certain you're getting the real thing, sometimes the only way is to get it from the manufacturer, or if they're one of those with obsolete ideas about wholesale-distributor-retail sales, from a specific vendor the manufacturer recommends directly.

Even aviation and military parts are counterfeited now, despite "supply chain accountability" and stiff penalties for getting caught, and it goes all the way down to "grade 8" hardware store fasteners that are actually made out of compressed Cheez-Whiz.

[Racer71]

I think the heavy piston contributed a lot to the failures on our engines as well. Arias sold a 14:1 piston for the Honda but it was much heavier than the 12:1 wiseco we typically use. I think many guys had issues with the weight of the arias and they out of favor with our group.

[Baprace]

Best photo of the sheared bolts....He will take a better photo...

It looks as the bolt on the right broke first. It’s shiny from the the two halves rubbing on each other. The other bolt on left has a rough grainy fracture and appears to have a shear lip.

From what I can see in the photo, one bolt failed and that caused the other bolt to break as the cap hinged open. If I had it to look at, or at least good photos with magnification, I could be more certain.

I agree with Keith, double click on the photo and it expands for a better view, I view the trouble began on the right bolt approx 2:00 position.

[MadBill]

I concur; looks like a fatigue crack originated there and grew to cover perhaps 20% of the bolt shank area before failing completely. Also, the left side joint face shows signs of the suspected 'hinging'.

[Geoff2]

We know the bolt failed. But why?

[allencr267]

Over revved?
An under-stressed fastener has a nearly infinite tensile fatigue life unless over torqued/stretched or a preexisting crack in a rolled/cut thread.

[Rick!]

Proper through-hardened screws usually don't appear grainy on failure. This is a hint.
Both bolts broke through their threads above the rod threads. This is also another hint.

It's hard to make a failure determination off of a low resolution photo.
Properly torqued bolts, even when subjected to bending, break in the first 1-3 threads of engagement as that is where the highest thread root stress is.
(the one attached article expresses the same observation)
Taking the failed parts to a metallurgical lab would yield the proper diagnosis.
If its a good lab, they have a sample of high zoot steel to compare to your bolts when a little mass spectrometry is done.

[MadBill]

A stand-up outfit like ARP might appreciate the chance to do their own failure analysis in the interests of QC and customer satisfaction.

[Truckedup]

I suppose this info from MAP cycle who market these rods and designed the originals my be helpful.. Carrillo still makes steel rods for these engines..The Carrillo rods are about 40 grams heavier each and make the balancing difficult....No one can say the lighter MAP rod is less robust...



Triumph T120 Bonneville 650cc 1959-72 (all years)
Triumph TR6 Tiger 650cc 1963-72 (all years)

Dimensions:

6.50 inches center to center
.688 pin size

Features:

Rods are balanced to +/- 1 gram
Unmatched quality - the best rods available anywhere for Triumph
"Solid Works" designed and stress tested
Machined from 4340 forging
Shot peened for stress relief
ARP2000 bolts (220,000 lb. tensile strength)
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Double wrist pin oilers
Unique reinforced small end critical areas without adding excess weight or cost

Finite element analyses design by High Cotton MotoWorks allows for:

Re-shaped pin boss for added strength (helps prevent "pin flex"& small-end failure)
Double “forced” pin oilers to reduce friction and piston pin heat
Bushed small end (replaceable) eliminating the need for fragile and expensive DLC pins
Optimized big-end and pin boss for strength with important weight reduction compared to other steel rods

[Kevin Johnson]

A stand-up outfit like ARP might appreciate the chance to do their own failure analysis in the interests of QC and customer satisfaction.

^^^^^^^^^^

[Truckedup]

Here's some close ups of the bolts and they are broken in the rod...click on photo for larger size