Rapid Transit: The 1986 Honda VFR750F Interceptor

To demonstrate the potential of its new powertrain, Honda management decided to build a sport bike that could be homologated for the 750cc AMA Superbike class. The 1983 VF750F Interceptor was the result, and although based on the V45 Sabre, the Interceptor also borrowed from Honda’s FWS1000 U.S. Formula 1 racer.

The VF750F used a perimeter frame of square-section steel tubes enveloping a strengthened 750cc V4. To allow for a shorter wheelbase and to give better weight distribution, Honda engineers tilted the engine back. The VF750F engine shared most components with the Sabre, though changes to cam timing and combustion chambers resulted in extra horsepower.

A more race-suitable chain final drive replaced the Sabre’s shaft, while the number of gears in the transmission went, curiously, from six to five. Apparently, reconfiguring the final drive for a chain meant less room for gears. The transmission also included a “slipper clutch,” with half the clutch plates driving the clutch hub through sprags, so the clutch was only 50 percent effective on the overrun.

The Interceptor’s front suspension used an air-assist Showa fork fitted with Honda’s TRAC (Torque Reactive Anti-dive Control) anti-dive system. Rear suspension was Honda’s own Pro-Link with a fully adjustable air-assist Showa shock. Wheels were Comcast alloy — 16-inch front and 18-inch rear — fitted with floating discs, two at the front and one at the rear, each gripped by twin-pot calipers.

As well as the prodigious thrust provided by 77 rear wheel horsepower, testers noted that this was, perhaps for the first time, a Japanese Superbike with a chassis that really handled.

Unexpected problems

Using essentially the same engine internals as the Sabre meant the Interceptor retained the former’s chain drive to the four overhead cams. And that’s where things started to go sideways. Within months of the VF750F’s introduction, customers were returning to their Honda dealers with mechanical noise from the cylinder heads. Upon opening customer engines, technicians found excessive camshaft wear and disintegrating cam chain tensioners. Curiously, not all bikes were affected — which made solving the problem even more challenging.

Honda’s response was a series of service advisories that tried to correct the issues under warranty. But the question still remained: What was the problem with the chain-cam engines? Many theories emerged, such as inadequate oil flow to the cams at low engine speed and careless valve adjustment.

A number of minor engine changes ensued, mostly aimed at improving oil flow to the cam boxes. There were also service bulletins entreating technicians to be especially vigilant about setting valve clearances. This may have helped with the cam wear issue, but it didn’t resolve the cam chain/tensioner problem. Tensioners could disintegrate in just a few thousand miles, causing further engine damage. Eventually, suspicion fell on an even more fundamental issue. It turns out that for the chain-cam-drive engines, the camshaft towers were simply milled out to accept the camshaft and fitted with off-the-shelf locating caps. This could allow the camshafts to move, compromising the mechanical integrity of the valve train. A special factory tool to correctly locate the camshaft during valve adjustment made a big difference, but it was clear a complete redesign was necessary.

Making it right

Honda’s long-fought reputation for engineering excellence was going down the toilet, and drastic action was needed. Fortunately, they had the solution in house. Honda’s FWS1000 racer and the European market VF1000R both drove their double overhead cams by gear rather than chain, and there was an important note in the press information for the 1985 introduction of the VF1000R: The engine, said Cycle magazine, had “new cylinder head castings to provide more camshaft support.”

Obviously, the gear-drive engines weren’t susceptible to cam chain/tensioner problems, even though valve operation from the camshaft was identical. The big difference was, in the gear-drive-cam engines, the cam bushings were line-bored with the locating caps in place, eliminating the camshaft location issues found in the chain-drive engines. Announced in late 1985, the replacement for the VF750 would use the same system. The VFR750F Interceptor of 1986 was the result.

The new VFR750F engine used a 180-degree crank instead of the VF’s 360-degree crank and featured six gears instead of five. New valve timing, revised carburetion and a bigger airbox increased power to a claimed 104 horsepower at 10,500rpm (though later dyno runs produced closer to 82 horsepower at the rear wheel).

The cams were driven by a “cassette” gear train running on ball bearings, operating individual rather than paired rockers with increased lubrication. The new engine went into a twin-spar aluminum frame with revised steering geometry, but with similar running gear to the VF750. The result was a weight reduction of 50 pounds, an 11.32-second quarter-mile at 122.11mph and a top speed of 144mph.

Driving camshafts by gear isn’t without its own issues. Gear lash can make accurate valve timing more difficult, and timing gears are noisy (as owners of Meriden Triumphs will attest!).

To get around the lash issue, Honda used a spring mounted “scissor” gear system — essentially two gears side-by-side and slightly offset — on the cam drive gears, offsetting the teeth by roughly half of the pitch. This allowed the lash to be entirely taken up by the tension of the two teeth resting together. The gear-driven cams went on to be a key feature of the later VFR750R.

A lot was riding on the VFR750F, and Honda was determined to get it right. And that they did. The 750 and later 800 Interceptors are widely regarded as some of Honda’s best, and remain in production to the present — although the cams are once again chain driven.

The VFR750F in racing

Though not designed as a race bike, the VFR750F inherited plenty of racing DNA from the RWS1000. In 1986, in one of its first outings, “Rocket” Ron Haslam took a standard VFR750F to third place in a Transatlantic Challenge race at the U.K.’s Donington Park race track. In the U.S., Fred Merkel and Wayne Rainey both contested the 1986 AMA Camel Pro series on VFRs, with Merkel taking the championship.

Riding Merkel’s old bike, Bubba Shobert finished third in the series in 1987, and his consistency on the VFR helped earn him the AMA Grand National championship. In 1988, Shobert won three of the seven races to win the AMA Superbike Championship aboard that same VFR750. 

Honda’s racing division, HRC (Honda Racing Corporation), also built six prototype racers with special magnesium engine cases. The engines also had titanium valves and used flat-slide carburetors. The “6X” (as it was known) weighed less than 370 pounds and produced around 135 horsepower at 13,000rpm. The 6X formed the basis for the 1988 VFR750R (RC30) homologation special, though it’s worth noting that very few parts are interchangeable between the “F” and “R” models.

Laf Young’s VFR750F

Laf Young is well known in AHRMA racing circles, mostly for the delightful 250cc 4-cylinder GP replica he built from a 1970s Benelli street bike. He came across the VFR750F featured here for sale on the island of Maui in Hawaii, where he lives. As far as Laf can tell, the bike was shipped to Hawaii from California carrying a salvage title and spent some time in Kona on the Big Island. It changed hands a couple of times for around $500, and was then acquired by Kelly Krail of Waikoloa.

Kelly carried out a full restoration of the VFR, spending at least $12,000 in parts alone. “I have nearly an inch of receipts since it came to the Islands,” Laf says. Apparently, Kelly traded the VFR for a rare Yamaha 2-stroke 500cc V4 that a local surfboard manufacturer had brought to Maui. Laf heard that Kelly had “cleaned up” the Yamaha and sold it for $15,000, but it seems he still has fond memories of the VFR. “I’ve had emails from Kelly,” Laf says. “He loved the bike [the Honda] and wishes he had it back.”

Laf is just enjoying owning the bike, learning more about the model as he goes. “One interesting detail,” he says, “is that the guys who raced it to great success — Fred Merkel, Wayne Rainey, Bubba Shobert — all abandoned the stock clip-ons in favor of an HRC-designed conventional handlebar. I suspect they preferred a little less weight bias on the front tire. I would give anything for the opportunity to buy or copy a set for my bike. The stock setup wears on my neck and arms after a long ride.”

As a value proposition, the Honda is waiting for its time in the sun. Young’s Honda may have been restored at great expense, but the market is going to take awhile to catch up with it — although there are signs it’s doing just that.

“One of my contacts attended the recent auction in Vegas. There was one VFR750F for sale. It was a Bubba Shobert replica and was quickly purchased for $5,000.” That was likely a very good price, especially considering its former owner was a certain Reg Pridmore. MC