Sooner or later every CB550 tells you it needs attention up top. Maybe it's a light metallic tick at idle that wasn't there last month. Maybe the bike's been sitting in a shed for eight years and you have no idea what the last owner touched. Either way, the answer lives under two aluminum covers on the top of the engine, and it's the same answer Honda wrote into the maintenance schedule fifty years ago: check the valves, then check the cam chain. They're the two most fundamental jobs on the bike, they're done back-to-back with the same covers off, and between them they're the difference between an engine that hums and one that rattles, runs rough, or quietly grenades itself.
Two of the longest-lived threads on the SOHC/4 Bikes board cover exactly these jobs — a valve-adjustment thread that's been read well over ten thousand times, and a cam-chain thread that's cleared nineteen thousand and keeps getting revived because it finally explains a mechanism the manuals manage to make baffling. Read together, they're basically the top-end tune-up chapter the factory manual should have had. Here's what the community worked out, in our own words.
Part one: valve lash is a feel, not a number
The valve thread starts where a lot of us start — a newcomer with a bike that's been parked for years, a Haynes manual, and a nagging suspicion that the printed specs might be optimistic. They aren't. The numbers are .002" on the intakes and .003" on the exhausts, cold, and the veterans confirm them without hesitation. One old hand's line is worth keeping in mind whenever you're tempted to "improve" on the factory: only very rarely did Honda's engineers leave anything on the table. Set them to spec and move on.
The genuinely useful part isn't the numbers, though — it's the method. Instead of chasing a single feeler blade until it feels "about right," the forum teaches the go/no-go approach, and once you do it this way you'll never go back. For an intake valve, the .002" blade should slide through the gap with a light drag, and the .003" blade should not go. If the .002" won't pass, the clearance is too tight — loosen the locknut and back the adjuster out. If the .003" slips through, it's too loose — snug the adjuster in. When the thinner blade goes and the next size up won't, you're done. For the exhausts you do the exact same dance one size up: .003" goes, .004" doesn't. That's why the regulars tell you to buy a .004" feeler even though it's not a spec — it's your "no-go" gauge on the exhaust side.
A couple of small things the thread will save you from. First, a proper tappet feeler gauge — the short, angled kind Motion Pro and others sell — turns this from a knuckle-skinning fight into a two-minute job, because a flat automotive feeler strip is genuinely awkward to seat squarely against these tappets. Second, don't be surprised if your "before" measurements are all over the map; the original poster found intakes and exhausts scattered from .003" to .006", which is exactly what a neglected engine looks like and exactly why you're in there. And on the eternal manual question, the room was split — some find the Clymer clearer, plenty find Haynes glosses over the important steps — but nobody argued the specs or the go/no-go method. That part is settled.
Part two: the cam chain tensioner everyone overthinks
If the valve job is simple once you know the trick, the cam chain tensioner is the opposite: it looks like nothing — one slotted screw and a locknut — and it generates more confusion, forum arguments, and wrecked engines than almost any other ten-minute task on the bike. The big thread exists because one member finally posted the mechanism in plain English, and suddenly the whole procedure made sense to people who'd been faking it for years.
Here's the mechanism, decoded. That slotted screw isn't something you turn to "tighten the chain" like a bolt. It's the visible end of a little half-moon gear inside the tensioner, mated to a spring-loaded rack. The design is self-adjusting: when you loosen the locknut, the internal spring is supposed to push the tensioner blade against the chain and rotate that screw on its own to exactly the right tension. Your job is almost nothing — loosen the locknut, let the spring do the work, then hold the screw still and re-tighten the nut. You are not supposed to crank the screw to a setting. As one of the forum's most-trusted wrenches put it, if you find yourself turning it, you've misunderstood what it does.
The correct starting position is #1 cylinder at 15 degrees after TDC on the compression stroke — and note the "after," because that single word gets mangled constantly. Even the FAQ that everyone quotes had it written as "before" for years until members corrected it in the thread; the whole point is to park the crank where the chain's slack lands on the tensioner side so the spring can take it up. There's a parallel manual argument too — the Clymer says 15 degrees, some Honda literature says TDC — and the practical resolution the veterans reach is refreshingly relaxed: it doesn't much matter where the engine sits as long as all the slack is in the rear run of the chain. Get the slack on the tensioner side and let the spring do its thing.
Now the two warnings that make this thread required reading. The first: do not force that screw. Over the years the gears gum up and the spring can't move freely, and the temptation is to "help" it with a screwdriver. The slotted ends snap under real force, and now you've turned a ten-minute adjustment into a teardown. If it's sticky, the accepted move is to gently exercise it in and out to free it up — not to muscle it. And the locknut is only a 10 mm; it wants a firm nip, not a gorilla, or you'll strip the threads on the stud.
The second warning is the one that can cost you the engine. There's a well-known "advanced" technique of adjusting the tensioner with the engine idling, listening for the noise to drop, then locking it down — and it does work for experienced hands. But the risk is real: with the locknut loose on a running engine, the chain can go slack enough to jump a tooth on the cam sprocket, and on these motors that can bend valves and end your afternoon. The forum's own framing is that this shortcut is done at your own risk by people who reckon they know better than the men who designed and documented the thing. Do the stationary adjustment by the book first. Only chase the last of the noise with the engine running if you understand exactly what you're risking.
Which brings up the diagnostic gold buried in the thread — how to know when the tensioner itself is dead versus just needing a set. The tell is the screw's travel: through its full working range that stud should only rotate a small fraction of a turn, on the order of a quarter turn, not more. If you can spin it a full revolution with no resistance, the internal rack-and-pinion is stripped — often because a previous owner forced it — and no amount of adjusting will hold tension. That's a replacement, and here the thread gets sobering: good tensioners are getting scarce (members trade tips on the last NOS units surfacing at dealers), and swapping one can mean pulling the head. Some got the new tensioner in without lifting the cylinders; others found that disturbing the head unsealed the base gasket and started a weep between the jugs and the cases that they're still living with. It's a job worth doing carefully, once.
The through-line
The most valuable single post across both threads doesn't come from either topic directly — it's a veteran reminding everyone that a smooth top end is an order of operations, not one heroic adjustment. Points, timing, plugs, valves, cam chain, then carb sync — done in that sequence, each one setting up the next. He also drops the insight that saves a lot of needless tensioner-fiddling: not every rattle up there is the cam chain. Some of it is the clutch basket, some is carbs that aren't synced yet, and the better everything else is dialed in, the quieter the whole engine gets. Chase the noise in the right order and most of it disappears before you ever blame the chain.
So if your 550 is ticking, resist the urge to go straight for the tensioner. Pull both covers, set the valves cold by go/no-go feel, do the tensioner exactly by the book and refuse to force it, and only then judge what noise is left. Nine times out of ten you'll find the engine you were worried about just wanted its scheduled maintenance — the same maintenance Honda printed in 1975 and the SOHC/4 crowd has been decoding ever since.
Full credit, as always, to the SOHC/4 Owners Club community for grinding these details out in public over the years — the go/no-go method, the tensioner mechanism in plain words, and the hard-won warnings that keep the rest of us from learning it the expensive way. If you own one of these bikes and you're not reading that forum, start today.
Once the top end is set and you're ready to build the rest of the bike the right way, that's our corner. Our Honda CB550 cafe racer parts catalog carries the tune-up consumables, gaskets and top-end hardware that make a maintenance job go back together clean instead of cobbled — so the covers come off, the work gets done right, and the engine goes back to humming.
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