Racer Brown Chapter Eleven

Valve Springs

Stock Datsun valve springs are quite light and generally are not suitable for valve lifts in excess of 0.440 to 0.460-inch. Besides they stack solid at a lift of about 0.500-inch. They're fine for stock camshafts, but they are the engine speed-limiting factor with camshafts having higher valve velocities. The type and number of valve springs, and consequently the valve spring loading, depends upon the type of camshaft and the application. For street or dual-purpose applications, we usually advise a single damper-type outer spring with a load of 70 pounds with the valves seated and 210 pounds at 0.500-inch valve lift. This spring will accept a valve lift of 0.600-inch without overstressing the spring wire, so it has a lot of latitude without causing and overload condition between the cam lobe-rocker pad interface. As a comparison, the stock L-series valve springs (they are the same now for all late L-series engines) have a combined inner and outer spring loading of 67 pounds with the valve seated and 165 pounds at a valve lift of 0.410-inch (stock L-24). The above-mentioned spring with a load of 70 pounds with the valve seated has a load of 188 pounds at 0.410-inch valve lift, so the difference in loading really isn't out of line. The stock L-series Datsun spring retainer is a very sloppy fit in this spring and with the stock retainer, the assembled spring length comes out about 3/16-inch too short, therefore we make a special retainer that is an interference fit in the spring and will also set the springs up at the correct assembled length and load.
For race-only engines, we advise a three-piece outer spring-damper-inner spring assembly. The springs are selectively-fitted to obtain an interference fit and the special retainers are an interference fit with both the inner and outer springs, all of which keeps the springs from waltzing about. With this combination, combined spring loading with the valve seated is 85 pounds with 370 pounds at the valve lift of 0.660-inch. While the latter figure may seem like lots, the 0.660-inch valve lift figure is lots, too.
Some special spring assemblies require that the valve spring pockets in the cylinder head be machined so that the inner and outer springs seat on the same level in the head. This does not imply that the spring pockets should be machined deeper in the head; it simply means that both the inner and outer springs seat on the same plane in the head, and the original spring pocket surface just barely cleaned. Deepening the spring pockets is courting disaster by puncturing the rood of and intake port, or by a highly-undesirable "ventilation" hole in the water jacket above and exhaust port, or both. Don't.
Because most special valve springs are both larger in diameter and longer, there are a couple of points where a hang-up could occur. Fist, in L-16 and L-18 engines, the valve spring and/or spring retainer may interfere with the cam towers on all four intake valves and number 1 and 4 exhaust valves. The corrective measure is to take a slight cut from the cam towers with a rotary file so there is no chance of interference at these points. This is usually not a problem with L-24 engines.
The second point of possible conflict could be between the underside of the rocker arm and the edge of the spring retainer when the valve is seated. This is more likely to occur with longer assembled valve spring lengths, but is should be checked out in any case. To correct for interference here, use a fairly large diameter sanding drum to relieve the rocker arm from actual contact, plus an extra 0.015 to 0.20-inch, then round off any sharp corners or edges on the rocker to prevent generating a stress-rise. Or, use the late-style rocker shown and referred to elsewhere in this chapter.
One of the nicest features of the L-series Datsun engines is the absence of pushrods, those rubbery objects that usually do more damage to the theoretical valve lift curve than anything else imaginable. All the L-series engines need is a good, dynamically stable cam lobe profile with enough valve spring load with the valve closed or open to prevent separation of the rocker arm tip and the lash pad at high engine speeds. The term "dynamically stable" simply means that the actual valve lift curve at the red-lined engine speed (maximum safe engine speed) deviates as little as possible from the theoretical valve lift curve, and still has a few hundred revolutions as a "cushion" against engine damage from a momentary accidental overspeed condition.
Thus with the L-series Datsuns, "overkill" with excessive valve spring loading si not only unnecessary but undesirable from the standpoint of accelerated wear of the cam lobe/rocker pad interface but also because higher valve spring loadings chew up horsepower. In additional, these is no way in the wide world that raising the valve spring loading can make a good cam lobe profile out of a bad one. A dynamically bad bump shape is just as bad - maybe worse -with a ton of spring load as it is with none. Any reputable manufacturer of Datsun camshafts and valve train accessories will (or should) have enough variety of valve springs, spring retainers, lash pads, etc., to satisfy must about any requirement within the realm or reason.
This doesn't mean that you should blindly accept his word for such things. Check out the spring load and assembled spring length dimensions to be absolutely certain that there is no possibility that the spring, or springs, will be stacked solid at or near full valve lift. There is nothing that is so quickly and completely destructive to the camshaft and valve train equipment as on or more stacked valve springs - and all it takes is an honest mistake in the valve spring load and/or assembled valve spring length dimensions on the timing card that accompanies the camshaft. Or, perhaps worse, the wrong valve springs with the correct specifications for the right springs.
In any cast, all inner valve springs (if used) should be checked at full valve lift, by themselves first, because it is not possible to see through the outer spring coils and damper coils to determine visibly if the inner spring is stacking solid at or near full valve lift. And some inner springs will stack before the outers, and some damper coils will stack before anything else. It therefore becomes mandatory to check each individual valve spring and damper coil to insure that stacking the valve spring assembly is not even a remote possibility. While you're running through this exercise, remember that the assembled spring length of the inner spring is always shorter than that of the outer spring by the thickness of the shoulder on the spring retainer, and in case stock Datsun springs are used, also by the inner spring shoulder in the cylinder head. A spring tester is the best way to handle this chore because spring length versus spring load can be measured simultaneously. If nothing else is handy, a drill press or even a bench vice can be used to measure spring lengths at the valve seated and full lift dimensions as a safeguard against stacking. Also, remember that only the springs are to be measured. Do not measure the spring retainers.
Valve springs, particularly race-quality springs, are among the most highly-stressed components of any engine assembly, but nothing lasts forever, so anything that can be done to ease the stress conditions of the springs will automatically make life easier on them and add to their longevity as well. Therefore, RESIST and AVOID the temptation of pulling the springs down to the last jillionth of an inch before they stack solid. All this accomplishes is an undesirably high spring load condition, but worse, causes premature spring fatigue, which ultimately results in spring breakage, and this is as bad as an armed hand grenade in the sump. Another bit of kindly consideration to the valve springs would be to remove the rocker arms if the engine is not to be used for a while to relax the springs at least to their installed lengths, then pour clean engine oil over them and drop the cam cover on to keep out dirt and moisture. If the engine is to be stored for any length of time, it's best to remove the springs and store them in a can of clean and covered engine oil. A valve spring that picks up a spot of rust will break. There is no argument or speculation about that; the only question is-when? Probably when you need it the most in one piece.

Valve Spring Detailing

A couple of other refinements are worthy of mention and consideration. The first is absolutely essential. Before the valve springs are installed, but after the valve stem oil seals have been installed, install the valves and assemble them with spring retainer and the top of the valve stem oil seal. If there is any conflict between this dimension and that of maximum valve lift, the seals must be removed and the tops of the valve guides shortened so that there is a least 1/16-inch between the bottoms of the spring retainers and the tops of the valve stem oil seals. There is usually no hang-up at this point unless the valve lift is 0.600-inch or more.
Next, it's a very good plan to remove the sharper corners and edges from the end coils of both ends of all valve springs and damper coils. This is done only at the points where the springs and dampers would contact a flat surface. Use a small, fine grit-sanding drum in a hand grinder or drill press. It takes only a touch to relieve the sharp edges and corners, which would otherwise gnaw away at the spring retainers and the steel shim that must be used between the bottoms of the springs and the aluminium cylinder head. When this is done, thoroughly wash the spring assemblies in clean solvent of lacquer thinner to remove all traces of abrasive dust, blow them bone dry with compressed air and dunk them in clean engine oil for the moment.
Checking Installed Spring Height and Other Details
Now we can install the valve springs, right? Wrong! There are a number of operations that must be carried out first that are best done with the head on the bench and without the valve springs. The first is to measure the assembled valve spring length in the cylinder head for each valve assembly, which for the moment consists of a valve, spring retainer, valve locks and steel spring shim. Keep each assembly separated from the others to prevent a parts mix-up during final assembly. Place the spring shim in the spring pocket, install the correct valve in the correct valve guide bore, slop the retainer over the valve stem, install the valve locks in the valve stem groove then pull up hard on the retainer to seat the valve locks on the valve stem and in the retainer. Apply upward pressure to the retainer to keep the valve on the seat and to keep the retainer and valve locks from coming loose. Use a 1-1/2-inch to 2-inch telescope gauge to measure the distance between the out flange of the spring retainer (for the outer spring) to the valve spring shim in the spring pocket. It is very important to keep the telescoping members of the gauge parallel to the valve stem in both planes. When the gauge is in the right position, lock it up, remove it and measure the gauge with a 1 to 2-inch outside micrometer. Comparing this dimension with the specified assembled valve spring length will tell you if the spring length is too long, too short, or within the specified length tolerance (usually plus-or-minus 0.010-inch). If the spring length is too long, add the correct number of shims to the spring pocket in the head and remeasure the assembled spring length again. This is not the place to goof off, so don't. If the spring length is within the specified tolerance, with the required one shim against the head, take the valve assembly apart, put it aside and repeat the process on the next valve assembly. At first, it feels like two hands aren't enough and three are too many, but two is the correct number.
If the assembled spring length is shorter than that specified, the problem can be solved in another way. But remember: DO NOT sink the valve spring pockets in the cylinder head any deeper than the original surface plus a clean-up cut of 0.010-inch, no more, and DO NOT sink the valves in the head. The standard L-series valve stem diameter approximates 5/16-inch and, by some coincidence, so does the Chrysler 426 Hemisphere street and race engines made from 1964 through 1971. Get yourself the required number of 426 Hemi valve locks; 16 for L-16 and L-18 engines and 24 for L-24 engines. These locks have keys that fir the valve stem groove about halfway in their length, whereas the keys in the stock Datsun locks are at the very tops. Using the hemi valve locks increases the valve spring length by about 0.065 to 0.075-inch, which may be enough to get the assembled valve spring length back into the right ball park. However, the Hemi locks are too long at the top and if used as is, the valve lash pads will contact the tops of the locks instead of the valve stem tips, a very unhealthy condition. So shorten the Hemi locks by about 0.040-inch from their top surfaces and assemble them with the valves and retainers to be certain that the valve stem tips project from 0.010 to 0.015-inch above the tops of the valve locks. This works and is entirely safe.
If the valve stem diameter in the Datsun head has been changed to approach 11/32-inch (as for use with FIA-type valves), see your friendly Chevrolet parts dispenser for the correct number of 283-327-350-400 Chevrolet valve locks. The same modification must be applied to the Chev valve locks as to the Hemi; otherwise they will fit and function as intended. That is, except for the possibility that the increase in assembled spring length may cause some interference between the tops of the valve springs and/or retainers and the rocker arms, as mentioned earlier.
Install the camshaft in the cylinder head using the proper Datsun service manual as a guide and also as a check for camshaft bearing bore-to-camshaft journal clearances. With the camshaft thrust plate and the camshaft sprocket in place, fore-and-aft movement of the camshaft in the head should be from about 0.008 to 0.015-inch. There are three thicknesses of camshaft thrust plates available so use the one that comes closest to the above fore-and-aft movement tolerance. At his point, it isn't necessary to have the camshaft retaining bolt as tight as it should be on final assembly, so an extra 0.002 to 0.003-inch fore-and-aft camshaft movement is OK for now.