push rod guide holes

Hi all,

I am running roller rockers with Chevy type push rods. I want to open the guide holes out from the 13mm holes now to about 18 this will mean going into the input ports by 2.5mm. Anyone have any experiance of this?

Yes just done mine. I have a 4.6 v8 I did my head gaskets only 5,000 miles ago but got a constant missfire after four thousand. On investigation I realised the the camshaft was worn out. As the heads were recon items and had been skimmed I didn't know how much had been taken off but with the new cam in place and with standard push rods I found the lifter preload was very high and all over the place. So decided to go for Real Steel adjustable push rods as I had tried shims under the pedestals to no avail!. The adjustable push rods were 5/16 so decided to drill out the guide holes. I experimented with a spare cylinder head to see how to deal with the swarf, there was quite a lot on each. The solution I found was to have a rubber hose long enough (cut to length) to have one end tight up against the hole to be drilled and long enough to be tight up against the opposite head bottom, this formed a tight bend so that when I drilled the guide the swarf would drop into the hose. I carefully released this pipe after each drill and shook out the swarf ready for the next one. At the top there is also a lot of swarf so this was collected, as I drilled, with a powerful vacuum cleaner. Obviously I had also covered every hole with paper towel, inc the long and tiny ones down to where the crank would be. I had cleaned heads prior too and after and still found some swarf in the little gulleys where the vacuum cleaner didnt do its work. So using some wd40 to wash them out and lots of kitchen roll and a pile of cotton buds to minutely go over everything including the four bolt holes which were full of oil and needed cleaning anyway, it was done! I am confident that I got it all, fingers crossed. I measured up the RS adjustables and had two millimeters removed from the ends before putting the push-on round ends (need a press). I have after some experimenting found a piece of wire tp 55/thou (as recommended by RS) and have started to install them. I found that from no slack to 55 thou is one full turn and two flats then tighten the lock nut, for some reason I had calculated that it should be one turn and three flats but after tigtening the lock nut go 60+ thou so I go one turn and two. I have had to make very slight adjustments as I go along but not much. I mark each push rod with prit stick so the flats can be counted and then on the rocker to show I had done that one. Wouldn't want to forget one!!