OHV valve train rocker shaft load

[DaveJFT]

Hi valve train gurus!

I'm designing a new OHV valve train and I'm trying to size the rocker shaft hold-down bolts.

Our dynamic valve train analysis has provided a peak load at the cam follower - cam lobe interface and I'm wondering how to apply that to the rocker shaft via the rockers. I have been searching around but have found conflicting information from two sources:

Source A says to take that load and simply multiply it by the rocker ratio to give the load at the rocker bearing.

Source B says to apply an equivalent reciprocal load at the valve tip, ignoring the rocker ratio but with the effect of simply doubling the load at the rocker bearing.

Which is correct?

Many thanks!

Dave

 

[BrianPetersen]

Draw a free-body diagram.

 

[EHudson]

The load on the rocker shaft is more than the cam lobe load: You have the cam lobe force pointing upwards towards one side of the shaft and on the otherside, the spring load is opposing the rotation, also pushing upwards against the shaft. Those loads add together. (Upwards is used because most shafts are on top the engine.) Now consider inertias and the valve and pushrod angles and make that diagram Mr. Peterson recommended.