What breaks rockers? (OHC hydraulic roller)

[BLSTIC]

Thinking about the Ford OHC Intech 6 (precursor to the Barra), accepted wisdom is that the stock rockers break between 6500 and 7500 rpm. But there's not really any concrete information on why, what else is going on, and if it can be avoided.

The rockers are cast (can't recall the material), roller cam follower with hydraulic tips. High ratio, 1.8-2.0 depending on generation.

Would it be a situation where it's just the necessary spring pressure and inertia doing this? Or would valve float play a part and a cam design that can control the valve better be ok at high rpm?

[Tom68]

Show us a broken rocker.
How old are the rockers that break.
What's the time frame at 7500 to breakage, will the ecu allow them to do a sustained 7500.
What's the time frame to breakage at 6500 ?

[RW TECH]

Usually what breaks those kinds of parts is an unstable valve train that has a lot of valve bounce at closing.

[mag2555]

Since production factory parts where not made with the intension of having a great reserve to being beat upon, you have simply found the cycling rate where they go south.

Since it’s cheaper then aftermarket performance ones ( even if there is such made) I would first send out a low mileage set to get cryo treated and see what that buys you.

[Dan Timberlake]

Depending where they break, blending and shot-peening high stress areas rockers can make a HUGE improvement in fatigue life.

I'd take pains to be sure to start with rockers ( new OR used) that have been 100% penetrant tested or wet method magnafluxed to cull out any with "indications" in the wrong place and oriented in the "wrong" direction.

BAd Geometry can overpower excellent materials.
The surface prep in critical areas can overpower decent basic geometry.

[BOOT]

What side is breaking, exh or int or both?