Honda VF1000R – A Chain Reaction
It’s generally acknowledged that Honda’s range of liquid-cooled, four-valve, overhead cam V-4s was rushed to market in response to an aggressive strategy by Yamaha to usurp Big Red’s title as number one in American sales.
Before the VF1000R, the first V-4 was the 1982 V45 (for cubic inches) Sabre for North America and VF750S sportbike in Europe. For the time, both had radically oversquare engines of 70 by 43mm, six-speed transmissions and shaft drive. They were initially acclaimed as technological tours de force: the short stroke, four-valve heads and narrow included valve angles were all state-of-the-art, and buyers anticipated high-revving, high-power performance.
The Flagship – VF1000R
The V-4 flagship model, at least in its pedigree, was the VF1000R. Derived from Honda’s AMA Formula 1-winning FWS1000, the R retained the FWS’s gear-driven camshaft arrangement, significantly the only bike in the V-4 street range to do so. Effectively, the VF1000R was a homologation special, built, initially at least, to qualify the bike for production racing.
All of the V-4 bikes though shared the same basic layout: a crankcase cast together with the cylinders; cast iron cylinder liners; chain driven double overhead camshafts; four valves per cylinder; and valves actuated by adjustable rockers rather than direct-acting shim-and-bucket. The chassis were equally revolutionary, using Honda’s Pro-Link rising rate rear end and TRAC anti-dive front fork.
The R was easily differentiated from the touring V1000F model by its full fairing, replacing the F’s handlebar-only item. However the main differences from the F model were inside the engine: compression ratio was up from 10:1 to 10.7:1; the camboxes contained more radical cams with longer exhaust duration. But the biggest change was in the way the cams were driven: the R engine contained a train of nine gears to drive the camshafts, replacing the central chain drive.
Though Honda had used gear drive cam operation in its racebikes, the VF1000R was the first of Big Red’s road bikes to be so equipped. Gear drive typically offers more precise and less variable cam timing at the expense of noise, weight—and cost. Honda overcame the noise issue in the VF1000R by incorporating a second set of teeth on several of the gears. These were flexibly mounted on the gear centre and slightly offset, with the intention of eliminating gear lash, the main noise source.
Unfortunately, the R didn’t really live up to its performance expectations. First, the revised cam timing resulted in more low- and mid-range torque than the F, but while the R delivered its maximum power of 92 rear-wheel hp at 9,500 rpm, according to one independently published dyno test, the F continued to build to 95.5 hp at 11,000 rpm. Added to that, the R at 610 pounds wet was a full 34 lbs. heavier than the F-bike .
Test riders at the time observed that the R felt at least as heavy as it actually was, and noted also the impact of the bike’s relatively high centre of gravity in both its resistance to changing direction and a tendency to pitch under heavy acceleration and braking. By comparison, the R’s main competitors, the Yamaha FJ1100 and Kawasaki GPz900R at 570 and 560 lbs. respectively—and both developing more power—were considerably more nimble, recording faster track times, higher top speeds, and quicker standing quarters. Neither were the ergonomics to any tester’s liking. The race-derived riding position required a long stretch over the tank and the high footpegs cramped riders’ legs.
Where the R came into its own was on fast sweepers and highway riding, where at around 100 mph (ahem …) the rider’s weight was balanced by the wind force. The general consensus, though, was that perhaps Honda should have sold the VF1000F in North America and left the R in Europe, where it enjoyed much more success.
WITHIN MONTHS OF THE INTRODUCTION OF THE VF750 IN 1982, customers were returning to their Honda dealers with excessive engine noise caused by rattly cam chains. On opening the engines, technicians also noted excessive camshaft wear. A number of minor engine changes ensued, mostly aimed at improving oil flow to the cam boxes. There were also service bulletins changing oil specifications while entreating technicians to be especially vigilant about setting valve clearances. This may have helped some with the cam wear problem, but didn’t resolve cam chain/tensioner issues.
The fragile tensioners could disintegrate in just a few thousand miles, causing further damage to the top end.
In hindsight, the V-4s were probably brought to market too early, with the unfortunate customer having to do the final development work. But why were only the cam-chain models affected? Obviously gear-drive engines weren’t susceptible to the cam chain/tensioner problems, but their valve actuation system was identical. There’s an important clue in the press information distributed for the 1985 introduction of the VF1000R. Going forward, the engine would host new cylinder head castings to provide more camshaft support, said the bachgrounder.
Eventually Honda discovered the real cause of the problem: the camshaft towers/caps were allowing the camshaft to move, compromising the mechanical integrity of the valve train. For the chain cam models, the camshaft towers were simply milled out to accept the camshaft and fitted with off-the-shelf caps. In the gear drive models, the towers/caps were line bored. A special factory tool to correctly locate the camshaft during valve adjustment made a big difference, but by this time the V-4’s credibility was shot.
The VF1000R remained in the fold for just two years. By 1987, Honda was in full damage control, and also had a new range of inline fours waiting in the wings. The V-4s were dropped, except for the gear-drive VFR750.
– Robert Smith Canadian Biker Issue #258
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