Quote:
Originally Posted by Alan Roehrich
If you're talking about the old red plastic "tool" that slips over the rocker stud, the best way to use one of those is to use it to take up space somewhere out of the way.
What you need is an adjustable pushrod length checker, Comp Cams has them. Use that on your engine, either mocked up completely (head gasket thickness included) or assembled, combined with a dial indicator that you can use to read valve lift at the retainer. Adjust the pushrod length checker until you get the correct lift and geometry for each valve and each lobe. Measure the over all length of the pushrod checker with a dial caliper, and order the correct pushrod. Thicker wall and larger diameter is better.
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Alan, I have just been working through this on my BB chev stocker, but after reading the previous thread am not so sure I'm correct in looking at just correcting the spec lift at the valve by lengthening the pushrods. I noticed that the longer pushrods create a wider "swipe" pattern on the valve stem, even as the lift is increasing at the valve. In my case, my cam lobe lift is .240" so would theoretically produce .408" at the valve with a 1.7 rocker. In fact, with light checking springs it was more like .420", way over spec. With a race spring and the same .120 wall pushrod, valve lift dropped into the low .380" range, to my thinking a huge difference. After installing a .100" longer pushrod, lift increased into the upper .380's, still way short of my legal max at .398".
The rockers are the re-inforced Holroyd units w/ his oversize studs, so hard to imagine that kind of deflection mainly in the rocker body, but these are the numbers I've been seeing. I'm now questioning whether the objective might not be to achieve the narrowest contact pattern on the stem tip, thus minimum side thrust and drag, then consider grinding even more lobe lift into the cam? Another poster suggested that, if I understood him correctly, that the pushrod tip and valve stem tip should each be at 90 degrees to the rocker stud and in line with each other with the lobe and valve both at half lift. I'd like to hear more feedback on those points from anyone who's researched this topic. I'm an old dog, but still tryin' to learn a few new tricks. Thanks to all who are contributing to this interesting subject!
Grant Eldridge
E/SA 6650