When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The factory's machine work on the spring pockets is VERY imprecise. They cut to some certain depth at a minimum, and then put in shims to take up the tolerance.
Then, over the life of the engine, when a valve job is done on heads, or for that matter when there's wear to the valve seat, the valve sinks deeper into the seat, making it stick farther up out of the guide, requiring even more shim thickness.
Shims are usually worn from the springs sitting on them, especially since stock ones are made out of crap soft metal, adding yet another variable to the randomness found on high-mileage stock motors. Aftermarket ones are MUCH harder and longer-lasting.
Setting valve springs to the correct height as specified for the particular springs that are being used, is one of the most basic steps of "building" a motor, as opposed to merely "assembling a box of parts". It is ABSOULTELY CRITICAL to getting the best performance and longest life out of a cam upgrade.
You accomplish this by measuring the distance between the pocket and the bottom of the retainer with a valve spring micrometer like this one https://www.summitracing.com/parts/pro-66902, subtracting the spec for your particular springs' installed height (usually 1.700" or 1.750" in these engines for typical replacement springs), and stacking up shims like these https://www.summitracing.com/parts/cca-4757/overview/
equal to the resulting thickness, to get the final installed height to as close as possible to the spec.
When it is stock the factory has put in enough shim to take up the tolerance left by the somewhat random machine work. They don't measure very carefully, not near as carefully as an engine "builder". They're pretty sloppy because for stock cams they don't have to be meticulous, it just has to be barely non-crappy enough to work.
No the heads do not have to be removed to remove the springs. Easiest way to do it is, remove all spark plugs; bring a cyl to TDC; stuff a couple of feet of nice limp rope in the cyl through the plug hole, about 3/8" (9 - 10mm) nylon works best, to fill up the cyl; take a socket, about a 5/8" (16mm or so) works best, and a BFH, and give the retainers a mighty whap. The keepers and retainer will fly off, which is no big loss, stock ones are garbage anyway. The spring might even fly off at the same time too. Turn the engine 90° and do the next one in the firing order (18436572). Repeat until complete. Replace all seals, springs, retainers, & keepers with new good-quality aftermarket.
Last edited by sofakingdom; 12-17-2017 at 04:51 PM.
12-17-2017, 11:11 AM
