I'm a GM mechanic, and i've done a few KA's, but the SR's are a little different... They have shims/spacers on top of the retainers that the rocker arm actually touches. I've heard that the size of these shims is extremely critical. Just curious what methods are typically used to calculate what size shims should be used. (I've heard Nissan makes .028-.032" for the shims) Also heard that all the slotted shims are the same thickness. Any info would help greatly. I have an idea i just wanna make sure it will work.

 

Yes the shim sizes and clearances are extremely critical to .001 of an inch. You can measure the shims with a micrometer but whats important is the clearances, between the rocker and cam lobe with the lobe facing out. You can use a feeler gauge to measure the clearances. The shims are all different sizes so keep track of where they belong.

 

The slotted shims (guides) only come in one size; 3.000mm. The flat shims come in sizes between 2.800mm and 3.200mm in 0.025mm increments. You can read these numbers off of the shim. A 2.800mm shim will read:
28
00

The spec for the maximum height deviation (levelness) is "less than 0.001 inch". Nissan has a special tool to measure this. It's basically a dial caliper on a bracket.

 

I have the tool, and shim heads for a fair price.

with standard HLA's you don't need to worry about cam to rocker clearance, only rocker height balance. mine are level to .0005" .

 

what about when you take ur head to get a valve job. they say they re-shim it. trust their work? or wait for abnormal wear, break some shit, and sue them for not doing it properly

 

if they do a valve job, you need to get it re shimmed.