Racer Brown Chapter Five

Valve Springs

All late L-series engines have inner and outer valve springs without flat damper coils. Valve open/closed spring loads vary with the type of engine and the valve lift.

Spring Retainers & Lash Pads

Valve spring retainers are upset steel stamping's with separate flanges for inner and outer valve springs. Tapered holes near the bottom accept single-groove split valve locks, mating with single grooves in the valve stems to secure valves to retainers in the normal manner. Nothing remarkable here. Spring retainer tops are counterbored to accept what is variously called a valve lash pad or a rocker arm guide. Whatever, it performs both functions. This pad is cylindrical with a slot machined through the centre of one side. This leaves two ears - one on each side of the slot extending upwards, away from the valve stem tip, and above the top of the springs retainer. The pad slip fits the counterbore in the retainer and the pad's flat bottom surface contacts the valve stem tip; they merely locate the rocker on the pivot. In addition, some of the side thrust transmitted from the rocker arm tip to the valve stem tip is eliminated and absorbed by the slip fit of the lash pad in the retainer, resulting in reduced wear of valve guide bores and valve stems.
In all of the Datsun cammer engines, valve lash is measured between the centre of the heel of the cam lobes and the rocker arm pads. Thus the amount of valve lash between rocker arm tip and the lash pad becomes a function of rocker arm ratio.
A "mousetrap" spring, with coils that straddle the rocker arm and which fits in a small groove behind the rocker pivot socket in the rocker, has free ends that hook into the butterfly clip in the rocker pivot bushing mentioned earlier. This spring exerts a fairly light load on the rocker arm to keep the rocker arm pad in (presumably) constant contact with the cam lobe as further insurance for correct rocker arm alignment.
Datsun's design involves a few more pieces than in more conventional single overhead camshaft layouts - but the number of pieces in any mechanism does not signify efficiency or inefficiency. Functionalism is the key here. In this respect the Datsun design is both original and clever. And it works!

Lubrication

Pressurised lubrication is delivered to the camshaft bearings by oil holes in each cam tower that line up with oil holes in the cylinder head, which in turn intersect with the main oil gallery in the cylinder head. In L-16/L-18 engines, the camshaft itself forms two additional oil galleries. These are drilled axially and on centre from each end for something less than half the total camshaft length, leaving a wall between the two galleries near the centre. The second and third camshaft bearing journals are grooved and drilled with an oil entry hole in each groove to admit oil into each of the two oil galleries in the cam. Each lobe is drilled to release oil under pressure to lubricate the cam lobe/rocker pad interfaces. Cam lobes for No. 1 cylinder exhaust, No. 2 intake, No. 3 intake, and No. 4 exhaust have oil holes drilled in the centre of the lobe heel. Exhausts 2 and 3 have the oil holes on the lobes opening flanks. For some mysterious and inexplicable (and unexplained reason, intakes 1 and 4 have the oil holes located on the lobes closing flanks, which makes no rhyme, reason or sense at all.
Historically, and as one might expect, No. 1 and 4 intake lobes are the ones most frequently damaged or distressed, along with their mating rocker pads - even in completely stock and unabused engines. It hardly seems likely that these two misplaced oil holes represent an oversight. However, it eliminates the need for a fourth indexing station, plus related tooling and machinery for drilling the am lobe oil holes at the factory. In any case, one of two possible fixes can make it right. Pressurised oil is contained within the camshaft by a press-in plug at the back of the camshaft and by the cam sprocket retaining bolt at the front.
L-24 cam bearings are lubricated in the same way as in the L-16/L-18 engines, but the cam lobe/rocker pad interfaces are lubricated in a different and much more satisfactory manner. An external steel tubing oil gallery bolts to Nos. 1,3 and 5 cam towers on the rocker. Pivot side. Oil to this gallery is supplied under pressure by drillings in the No. 3 cam tower. Short transverse pipes aim oil streams directly at each of the cam lobe/rocker pad interfaces.
This system works admirably; so well in fact, that it has been more-or-less duplicated on a good number of modified L-16/L18 engines with equal success. When this has been correctly done on the four-cylinder engines, there is no longer any need for interface lubrication from the cam lobe oil holes. Oil sources to the hollow camshaft should be blocked off because they create a relatively large and unnecessary oil leak, which robs oil from the main and connecting rod bearings.
Oil entry holes in the grooves of numbers 2 and 3 camshaft journals must be plugged by drilling and tapping the holes for small socket-head setscrews. Use a bottoming tap to about 3/8-inch depth so the setscrews will bottom out tightly in the oil holes. The heads of the setscrews must not extend beyond the bearing journal surfaces. Loctite the setscrews to secure them. Also, remove the bolt at the front and the plug at the back of the camshaft so all chips can be scrubbed out. Otherwise the chips will inevitably find their way to the cam lobe oil holes with catastrophic results when they become trapped between the cam lobes and the rocker pads. Upon completion, there is no need to replace the rear camshaft plug (which you had to drill out to remove).
Enter SCCA. This August group occasionally comes up with some seemingly odd and misguided rules and regulations - and that's being charitable. According to their 1973 rules, SCCA hath decreed that the L-24 type of external oil gallery is not legal in L-16/L-18 engines. However, some clever lad who shall remain nameless circumvented this ridiculous rule by soldering copper "cooling fins" to his modified L-24 bolt-on external oil gallery. SCCA makes no distinction about the number or location of oil coolers for any on vehicle, so the cam lobe/rocker pad interface lubrication system magically becomes and "oil cooler" - entirely legal and acceptable by SCCA.
If one wishes to retain the stock L-16/L-18 cam lobe oiling system, it is a simple matter to drill intake lobes 1 and 4 with an additional oil hole each, this time locating the new oil holes on the opening flanks of the cam lobes. The cam lobes aren't all that hard, so tungsten-carbide drills are not required. A good, sharp high-speed steel twist drill will do the job. Use a number 47 drill (0.078-inch diameter) or a 2mm drill. Again, thoroughly clean both camshaft galleries before reassembly. This time, replacement of the rear camshaft plug is essential.
With either oiling system. It isn't difficult to imagine the volume of oil being sloshed about under the camshaft cover. Looks like Signal Hill all over again. This condition demands an effective oil drainback system from the cylinder head to the crankcase. In the front, a large hole empties into the crankcase through the timing chain cover. At the back, a 9/16-inch diameter hole empties into a matching hole through the block. This seems small but the top of the head is nicely channelled to direct drainback oil in either direction, effectively preventing an increasing oil level in the head…the wrong place to be of any value.