Yanmar 4JH4-TE Catastrophic failure

[Hunterdog]

Here’s some close ups of the broken bolt...

[Hunterdog]

Here’s the epilogue to this disaster:
https://youtu.be/ovDdiq_QSJ4
Enjoy!

[col50]

How can it be that one rod bolt breaks and the other one stays intact?
If one bolt breaks and the bearing-cap is no longer supported on one side, the other bolt will bend and eventually break. This is not what happened.
This disaster obviously did not start with a broken rod bolt.

[skipperpete]

Originally Posted by col50

How can it be that one rod bolt breaks and the other one stays intact?

If one bolt breaks and the bearing-cap is no longer supported on one side, the other bolt will bend and eventually break. This is not what happened.

This disaster obviously did not start with a broken rod bolt.

That was covered earlier in the thread by a thoughtful observant poster. He suggested that the bolt was loose and just fell out then ....lthe other one snapped off clean. This was later verified by the OP who found the relatively unscathed rod bolt in the oilpan.

[Hunterdog]

Originally Posted by skipperpete

That was covered earlier in the thread by a thoughtful observant poster. He suggested that the bolt was loose and just fell out then ....lthe other one snapped off clean. This was later verified by the OP who found the relatively unscathed rod bolt in the oilpan.

How can one prove that a bolt loosened and fell out?

[skipperpete]

Hi ,Hunterdog , I’m happy to see you got the new engine in, good video!! Logically there is no other explanation for that bolt , not stripped,bent or basically harmed in any way to be laying in the oilpan.
If both came loose there would have been damage from pounding for as long as it took to shed that bearing cap. The fracture of the failed bolt is clean and I suspect it was very sudden, not prolonged.
I can’t prove it but I also can’t think of any other way to explain the good bolt in the oilpan.
Cheers, Pete.

[col50]

Originally Posted by col50

How can it be that one rod bolt breaks and the other one stays intact?
If one bolt breaks and the bearing-cap is no longer supported on one side, the other bolt will bend and eventually break. This is not what happened.
This disaster obviously did not start with a broken rod bolt.

I'll take all the above back.
Apparently I did not read all the posts and missed the fact that a mostly unscathed bolt was found in the oil-pan.
I think RaymondR came up with the correct explanation in post #164.

[rlamoureux]

Dear Hunterdog, has Yanmar given you a probable cause of the failure i.e. is it something that happens "normally" with age? What year was it manufactured and how many hours did you have on the engine?

Don't take this question the wrong way but had you checked the oil level recently?