Hi - I am just starting a rebuild of a 256, and have come across an interesting subject in the James Eickman book that says;  

"Camshaft and lifter life can be increased dramatically by modifying the block. Drill and chamfer a 1/4inch hole at the base of each lifter bore boss except for the two at the rear of the block. Then grind grooves along the boss and connecting with the hole."
Is this a standard practice with rebuilders - will it prove a benefit - do you guys normally do it? what issues may I have +

Setting up the new CAM - what actually defines the amount of backlash or end play - should the rear welsh plug be fitted first - how far in the block should it sit?

Lots of question I know but I want to get it right 

 

It has been found that the additional holes in the valley are beneficial to providing additional crankcase pressure relief but provides no benefit to camshaft lobe or tappet oiling.  Here are links to previous threads on the subject.

Drilling additional holes for oiling and/or venting

Valley holes for aiding crankcase evacuation

Lorena, Texas (South of Waco)

Typical camshaft end play is 0.004”- 0.006”.  The service manual says 0.012” max.  This clearance is dictated by the cam thrust washer and thrust plate thicknesses with the washer being the thicker of the two.  The washer itself must be installed on the camshaft with the chamfer facing the rear.

The rear cam plug should be installed flush with the back of the block with the cup facing rear ward.  This requires using the correct plug and not a deeper dish style of plug.  If all is well, you should have the cam falling at least 0.020” behind the front face of the block before installing the cam gear hardware.

Here’s the link to the rear cam plug article that was in the Y-Block Magazine.

http://www.eatonbalancing.com/blog/2011/10/21/rear-camshaft-plug-installation/

Lorena, Texas (South of Waco)

Hi Ted
- Thank you, its interesting to get another view - clearly the extra holes are not as critical as I had thought - I'm glad I asked about the rear welsh plug - I'll check for a shallow one now
Gordon