Rocker shims = NO rocker shaft oiling
So….. you had not enough lifter preload, so you put shims under the rocker shafts. Would that not raise the shafts and decrease the preload even more? Also, decking the heads would increase not decrease the preload.
Am I missing something in your explanation?
Yeah, You're missing something. There are 2 schools of thought in setting lifter preload;
1) Very little preload, so that at rpm, the lifters are limited in their ability to "pump up" during lost valve motion. I am in that camp, and if You've watched enough high speed/sample-rate video of valvetrains, there is
always some lost motion no matter how good You think your springs are. If they pump up, the valves don't fully seat & you've got a sag in the curve or the top end is soft. Make no mistake, even if the valve seats, it's going to bounce a little anyways.
2) Set the preload almost to the bottomed-out position, so that any operating deflections can be compensated for, and if the lifter oil supply/feed actually causes the lifter to bleed down at rpm, it can only lose a tiny bit of lift & is less likely to toss an unguided pushrod out. Vizard is in that camp.
In either case, You are compensating for shortcomings of a hydraulic tappet, some can be minimized & some come with the territory.
