VF750 and ZX900 cam failures
Honda and Kawasaki made rocker arms whose surface hardening consisted solely of chrome plating. In many instances, this chrome failed, just as it has in many of Honda's SOHC fours. The problem bikes are any with the four-valve Kawasaki ZX900 series engine, including the early 80s 900 Ninja, Concours 1000, and the 900 Eliminator, as well as all first-gen Honda V4s, 700cc and larger. And as mentioned, to a lessor extent the 70s four-cylinders. The Kawasaki 900-based engines and Honda's early V4s have some other things in common that make them especially vulnerable: tandem rocker arms with four valve springs exerting high pressure on the cam lobe, combined with high valve lift, plus one more factor. All these engine's cams were cast extremely close to finished size, then lightly ground. Cavities (engineers call them "inclusions") were produced in some of these cams immediately below the surface. Via normal cam wear these pockets revealed as pits. If large enough, the pits then abraded the rockers' chrome plating, making it fail (buckle and peel), and the rocker arm then became a "cheese grater" that quickly took out the cam. These cam failures have nothing to do with lubrication, heat, valve adjustment, or anything else unaware folks have attributed to them. Only engines having the four things in common: chromed rocker arms, tandem rocker arms operating two valves, very high valve lift, and cams made in ways that produce unseen cavities, experience the famous severe cam failure. The Honda SOHC fours lack the tandem rocker arms and high valve lift. So while they still have chrome plated rocker arms and cavity-infested cams, their cam destruction is far less common. However, SOHC four rocker arms do eventually peel or wear prematurely their chrome, to the degree that aftermarket cam makers will not guarantee their product unless the rocker arms are replaced. That chrome plating stands out as the single most significant issue, whether 70s or 80s model Honda engines.

Cam bearings
Cams are bolted into Honda multicylinder engines in ways that are surprisingly low tech. First, there are no bearings other than the cylinder head surface combined with the hold-down clamps, or "holders" the OEMs call them. I will refer to them as bearings, which, combined with the bearing "saddles" in head, they in fact are. While the alloy used in the head is specially designed to be friction resistant and often will fail after (yes, after) the cam does, the steel/aluminum interface remains a potential point of failure, especially when high pressure, high flow oiling to the cylinder is for whatever reason compromised, including dirty oil and low oil level, factors unfortunately common enough among the owners of these machines,

These cam bearing clearances are surprisingly large, usually 0.005" on Hondas. Some racers have reduced this clearance successfully. An esoteric point. More importantly, this clearance combined with superlative Honda manufacturing, is what makes it possible to interchange cam bearings from one engine to another without problems, despite the typically unintelligent warnings on forums.

An equally important observation is that, over the decades, as valve lift has steadily gone up in production models, cam holders have morphed from the individual holders of the 70s and 80s into the full size hold-down plates today's engines have. This full width plate design resists the flex that would otherwise lead to failure as a result of the later models' much higher valve lifts.

The bearing bolt torque specs in many OEM manuals--including Honda's--are incorrect, and using them results in over-torquing leading to bolt failure. Honda often specifies 12 or more foot-pounds for the 6mm holder bolts. This is excessive. Every mechanics school student knows that A) a foot-pound torque wrench is the incorrect tool for a 6mm bolt; and that B) a 6mm bolt is never tightened over 90 inch-pounds in an aluminum engine, and preferably to less.

Over-torquing these bearings produced another issue. Kawasaki published a warning about the KX250F. These bikes' camshafts have their sprockets pressed on at the factory instead of bolted on. Overtightened bearings have been proven to increase cam friction to the point that makes these sprockets slip, and since they are not marked, that is, indexed, a slipped sprocket is easy to overlook, and for the average person impossible to correct. Early Yamaha and Kawasaki four-stroke motocrossers were famous for this.

Valve springs, valve guides, and valve guide seals
Honda valve springs are recognized among veteran mechanics as the best in the industry. Almost without exception, aftermarket springs do not offer any improvement. Whether resurrecting bikes that have sat for years, or racing vintage Hondas, the stock springs have proven their worth. Honda's valve guide seals were once equally famous; mechanics used to put Gold Wing seals on Kawasaki Z1s. And the cast iron guides found in Big Four engines are worlds better than the non-ferrous guides some racers use. They use them because they are more readily available, they ream easier, and theoretically they add cooling to the valves. They're a poor choice outside of racing however.

This valve cover came from an 1982 Honda VF750 Sabre. Someone left a valve adjustment screw locknut loose and it rocketted theough the cover at high speed. That's a big hole! The wrench in front of the cover has a story all its own.

I'm always surprised when I find valve adjusting locknuts only gently snugged. This is risky. The velocities that the ends of the rocker arms reach are astronomical. That tiny locknut can and has rocketted right through a quarter-inch thick cast aluminum valve cover, leaving behind a gaping two-inch diameter hole. For one model prone to this Honda even issued a special extra-long tightening wrench. But overtightening isn't a good thing either. Though the adjusting screws are hardened, rocker arm screw threads go bad from overtightening of the locknuts, which then makes adjusting clearances an aggravation as the screw insists on finding its same place every time until the nut is tightened.