Class 12.9 alloy steel on connecting rod

[borna]

Hello all,
I am working on this Chinese engine and I am missing one 2mx6mm screw for the connecting rod, which I ordered online from Bolt Depot. When the package arrived, I noticed it said these hex screws are "Class 12.9 alloy steel." Since the connecting rod is made of bronze or possibly brass, and Class 12.9 alloy steel is very hard, would that cause an issue using it with the brass or bronze? I am concerned that the continuous cycle could either cause the screw to break since it is very brittle or damage the threads on the connecting rod. Any thoughts on that?

 

[JimSvarv]

I don't see why it would damage your threads if they are using the same torque as before.
Not sure how 12.9 compare but arp high tensile bolts are used in aluminium rods.
The book Four-stroke performance tuning recommends loctite on the fasteners on the big end.

What engine is it that you have?

 

[GreenTwin]

I order SAE grade 5 bolts, as a minimum strength.

It looks like 12.9 bolts are quite a bit stronger than grade 5.
I am not sure how brittle the high strength bolts are, but if they were very brittle, they would not make a very good high strength bolt.

I would agree with Jim, just don't overtorque the bolt.
And Loctite (tm) recommends the low strength blue product to prevent electrolysis between dissimilar metals, and also to prevent the bolt from working loose due to vibration.
.