Road Bearing break-in period? (help)

[alifsyz]

I am about to replace my busted rod bearings on my M50. I was wondering if there is a break-in period for the rod bearings, as some knowledgeable people suggest going 5000KMs then an oil change. All the help is much appreciated. Thanks!

[ForcedFirebird]

I never sweat the rod bearing break in. I have built countless race motors and put them on the track right after the build, and breaking in the rings/cam.

[wworm]

I never sweat the rod bearing break in. I have built countless race motors and put them on the track right after the build, and breaking in the rings/cam.

What kind of ring/cam break in period do you usually run?

[ForcedFirebird]

High idle for ~20 min after initial warm up with break in oil (or oil with high zddp). Then lots of engine braking for a good 30-40min (drive until ~6000rpm in 2nd, let engine slow car, downshift to 1st, let engine slow car, rinse and repeat). Change and inspect oil. Do a race practice at 80%, change oil, then go beat the snot out of it.

[alifsyz]

High idle for ~20 min after initial warm up with break in oil (or oil with high zddp). Then lots of engine braking for a good 30-40min (drive until ~6000rpm in 2nd, let engine slow car, downshift to 1st, let engine slow car, rinse and repeat). Change and inspect oil. Do a race practice at 80%, change oil, then go beat the snot out of it.

I heard from one of my friends that they broke their new rod bearings after an extensive hooning session right after replacing it. Do you think this is because of something else? Thanks.

[ForcedFirebird]

I heard from one of my friends that they broke their new rod bearings after an extensive hooning session right after replacing it. Do you think this is because of something else? Thanks.

Not trying to be difficult or blunt, but my experiemce says otherwise.

Think about it. If you buy a brand new car, go hoon around in it, how often do you hear of failures?

[digger]

What could "breaking in" a rod bearing possibly do ? It's a hydrodynamic lubricated bearing. The surfaces of the journal and bearing shell do not need to wear in together unlike rings, valve seats, cam followers, gears, etc

[alifsyz]

Not trying to be difficult or blunt, but my experiemce says otherwise.

Think about it. If you buy a brand new car, go hoon around in it, how often do you hear of failures?

Could it be misassembly then?

[alifsyz]

What could "breaking in" a rod bearing possibly do ? It's a hydrodynamic lubricated bearing. The surfaces of the journal and bearing shell do not need to wear in together unlike rings, valve seats, cam followers, gears, etc

Thanks man! Very informative.

[ForcedFirebird]

Could it be misassembly then?

More than likely. Bearing clearance is critical. On the m5x/s5x (except s54 and Euro s50), and m20 which all use the same rod bearings, you should have a clearance between .001 and .0015" (.025mm-.031mm).