Honda CBR600F - CLASSICS REMEMBERED

Who could have predicted it at the time? A product of Honda's internal competition between the in-line design group and the V4 group, the compact 397-lb in-line 600F of 1987 was a low-cost steel-framed solution to the problem of taking the lead in the emerging 600 sportbike class. Yet today, we must pay $11,500 to own the latest hot example of that class. The rapid yearly performance upgrades necessary to make these bikes win the Supersport races that motivated sales eventually drove ownership out of reach of many potential buyers. Yet as recently as just before the Depression of 2008 hit, 600s were widely considered "entry-level bikes".

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The 63 x 48mm = 598.5 four-valve liquid-cooled six-speed CBR600 engine of 1987 continued a practice Honda had developed for its GP engines in 1961 – that of casting the upper crankcase and cylinders in one unit. This braced the crankcase against the flexure that, in designs with separate cylinder blocks, can lead to base gasket wear and leakage (as in your basic Kawasaki Z1-based Superbike engine at 10,250-rpm). The steel tube chassis was praised at the time for being a price-cutting solution. This was in contrast to the rapidly rising sophistication of all makers' 750s, which had rapidly adopted aluminum chassis and swingarms, plus the beginnings of adjustable suspension. Every maker was riding this trend in hope of winning in high-prestige AMA Superbike racing. It was hoped that the new 600 category could avoid this upward spiral of expense.

It was so important to Honda to have these 600s at Daytona that year that the bikes arrived before the normal suite of rebuild and crash parts – such things as gaskets and hand- and foot levers. A special dispensation was sought from tech not to tear the engines down because without new head gaskets they would miss the next national.

In style, the CBR600 was clearly influenced by a short-lived European trend toward complete smooth enclosure, epitomized by the late Massimo Tamburini's Ducati 'Paso'. Within Honda, the V4 group, inheritors of the plusses and minuses of that company's oval pistoned NR500 V4 GP bike, had enjoyed dominance of AMA Superbike with their V4 VFR750s, but the in-line group was thought even then to have competing designs ready for production – maybe with lower production cost. It would take time for public opinion to assemble itself, but its final decision was clear; the V4s were shunted off to a new role as "gentlemen's sport-tourers" (in industry-speak, "gentlemen" means guys in their 50s and 60s who can't ride sportbikes without their bad backs acting up), and the in-lines were gradually deployed to do battle with the similar bikes of the other makers.

A benefit of full fairing enclosure as on that first CBR600 was the end to the expense of engine beautification. Bikes with engines visible require cosmetic enhancements, but with everything covered up, no one sees the engine so it can just be its ugly old self, covered in hoses and wires.

The CBR600 certainly raised the bar in the class, with 85-6-hp @ 11,000. Its 1.3 bore/stroke ratio was a long jump beyond the one-to-one that had been usual for the 1000-cc air-cooled sit-up bikes. A normal problem of air cooling is how to limit piston temperature, for without the complication of crankcase-mounted piston oil cooling jets, the only path heat can follow out of the pistons is across the crown to the cylinder wall, then down to the piston rings which are in closest contact with it. The quick fix? Shorten the heat path by keeping the bore diameter on the small side. Why make the CBR’s bore bigger than its stroke? To make room for the valves needed to fill the cylinders at peak rpm higher than the 8-9000 that had been the usual limit for production air-coolers. Yes, souped-up air-cooleds can certainly rev higher than this, but unlike private tuners, manufacturers have to back their product with warranty.

CBR600, with its water cooling, now had much cooler cylinder walls to suck heat out of its pistons – even if they were on the large side. That 1.3 bore/stroke ratio was where Keith Duckworth began with his epoch-making DFV F1 engine of 1967 – whose fairly flat combustion chamber (32-degree valve included angle), flat-topped pistons, and four valves with one central spark plug remain the basis of most four-stroke engines produced today.

Naturally, as 600 competition heated up, American Honda and the others weren’t going to leave the winning of 600 Supersport races up to whoever happened to buy and race them. They had top pro riders on payroll so it made best sense to put them on carefully prepared and factory-entered bikes.

What did “carefully prepared” mean? I always used to wonder about that. Did it mean taking an hour to ever-so-gently lower a fanatically clean stock crankshaft onto its stock bearing inserts? Mm, maybe in some cases. But put an ear to the ground and hear some of the colorful stories from that era:

This in a Supersport class, supposedly limited to a valve job (no metal removal anywhere but from the valve seat rings), a smokestack, tires, brake pads, and suspension upgrades.

But wait. By definition, anything that comes out of the factory is stock, right? When I was a tech inspector, I asked team managers for factory specs on critical dimensions and was always told the same thing;

“Yeah, well, if it’s not in the service manual, we can’t get it. And anyway, we got three, four suppliers for every part, right? And each one o’ them has his own go/no-go numbers. Sorry – we can’t help you.”

Bottom line; no specs exist.

So into my imagination (later confirmed by other means) came this idea. Mr. Tanaka walks onto the production floor and over to the automatic machine that’s busily finishing wristpin holes in pistons. Like all such machines, it has a screen and keyboard, and a big red STOP button. Tanaka gives it a practiced whack and places his hands on the keyboard. A few strokes and he has increased wristpin-to-crown axis height by an amount too small for any reasonable tech inspector to object to. But big enough. He hits START, lets the machine run off 100 or so pistons, then directs his assistant to collect them. He does something similar at several other machines. With the slightly-off-spec parts thus produced, a small team of engine builders assembles “tolerance stack-up specials”, all of whose parts err in the same direction – toward higher compression ratio.

This only helps you if you’re the first to do it. After everyone’s doing it, everyone has to just to stay even.

600s brought all this fast-accumulating race tech to the public, as each successive model incorporated more advanced features - bigger bore, higher rev capability, lighter valve train. At the end of the collective madness, World Supersport versions of 600s were supposedly making a somewhat brittle 140-hp up at 16,000 or so. New stockers were making the same power as factory Supersport racers just five years previous. Supersport racing rapidly raised the level of motorcycle agility, setting a high standard.

Honda learned at least one valuable lesson from the 600F; quick reliable shifting required higher surface finishes on certain parts than those first CBRs were getting.

Honda in-line 600 and 1000-cc fours have carried the sportbike banner for years now despite periodic rumors that “Honda’s coming with a fabulous 1000-cc V4 sportbike that will make everything else obsolete.” They did make a few V4 NR750 oval piston street bikes for collectors back in 1992, and in 2015 came the limited-production V4 RC213V-S MotoGP replica-for-the-street, but with disappointingly limited power. And now we hear Honda will discontinue CBR600 sales in Europe, while the whole sportbike category has taken a big sales hit since 2008. So who knows what’s next?

Be happy for all the good times enjoyed by thousands of riders on the long series of CBRs.