The following article is reprinted from the March/April 2000 issue of Classic Racer.
The Spirit of Mann
M3 Racing's Replica of Dick Mann's 1970 Daytona-Winning CR750 Honda Topped the AHRMA Formula 750 Championship in 1998 and '99. Now the team is planning to make it three in a row.
Robert Laver Reports
Every good story deserves a sequel. America's M3 Racing has written one for the CR750 Honda. The sohc four built by M3 boss Mark McGrew has two Formula 750 AHMRA championships to its credit and stirs memories of the great Daytona victory Dick Mann scored on the original factory racer in March 1970.
That's when and where the first story began, with an unforgettable opening scene in the Florida sunshine...
The CB750 caused a sensation when it made its public debut at the '968 Tokyo Show. It was the first modern superbike and set the trends still current today. The first showroom models arrived in America the following year. Honda had quit GP racing in the late '60s but saw the 1970 Daytona meeting as a perfect showcase for the CR race version of its new king of the road.
The opening round in the AMA calendar was enjoying a renaissance. BSA-Triumph was out to grab the headlines with its own new superbike, and the showdown between the British triples and the Honda-4 on the high-speed Daytona banking promised to be a sensation. Honda signed four riders to spearhead its attack- Ralph Bryans, Tommy Rob, Bill Smith and former AMA champion Dick Mann. The American was its best performer in practice, finishing fourth behind a trio of BSA-Triumph triples whose pilots included Mike Hailwood. Mann's teammates were not so lucky. Bryans' machine caught fire and burnt out, and the engines of the other two bikes blew up.
Mann, with thousands of miles on the speed banking behind him and a wealth of experience in building and preparing his own engines, decided to play it safe by gearing up his machine to save the engine from overrevving.
The race was hard and fast. Of the 80 starters, only 15 made it to the finish and it was Mann, rattling camchain and all, who led them home, followed by Gene Romero and Don Castro on the British triples.
That success got the ball rolling. Honda offered its importers special race kits to turn the road bike into a track star. A few complete bikes were also shipped out from the factory, but it was the DIY kits which interested most bike builders and tuners.
The list of goodies included wheel rims, wheel hubs, disc brakes and lightweight fork legs. There were also service sheets giving instructions on modifying standard components to race specification. The list of special parts grew to include mudguards, fork crowns, fuel tank, seat unit, oil tank, sprockets, carburetors, exhaust system and fairing. Nor did it stop there. Mods for the engine came in the form of camshafts, pistons, conrods, valves, a lighter crankshaft, new gearbox shafts and magnesium covers. Superlight fasteners, cables, hoses and grips were also part of the process of transforming a CB750 into a CR racer.
As most of the parts were sold separately, very few bikes were exact replicas of the Dick Mann Honda. In 1987, Mark McGrew decided to build himself the real McCoy. The special bits necessary for such an undertaking were never particularly plentiful in the first place, so tracking them down nearly 10 years later was no easy task. There was one other problem - they cost a fortune!
Mark called on his contacts within the Honda organisation and succeeded in creating a machine that was snapped up for display by the famous Barber Museum. Mark, a glutton for punishment, then decided to repeat the whole exercise and build a second bike to campaign in AHMRA events as a showpiece his M3 Racing company. Work got underway in 1995 AHRMA regs allow an extra millimetre of bore, which Mark took advantage of to increase the engine capacity to 76ICC. Other peculiarities in the rule-book allow drilled discs, open exhaust, the use of us-octane racing fuel and up to a VM; rear wheel rim. The result is the bike Adam Popp raced to success in the 1998 and 1999 AHMRA F750 championships.
Mark builds his own engines and has paid special attention to this one. He had Mega-Cycle draw up a special camshaft, designed his own camchain tensioner and drives the valve gear with a Tsubaki racing chain.
Between 10 and 15 hours were spent lightening, polishing and balancing
the crank, and he modified a Dyna ignition system to his own spec. A close-ratio
Nova gearbox partners the Honda clutch in which Mark runs fibre plates.
The search for a genuine Honda race exhaust system was unsuccessful, so
Mark commissioned Rob North to build him an exact replica based on factory
The cycle parts include front forks from a 1982 CB750 with 37mm stanchions, CBX fork crowns and aluminum shocks from Progressive Suspension. The two 296mm stainless steel front discs are just 5mm thick and are braked by Grimeca twin-piston calipers. The rear wheel hub is a replica of the one used on Mike Hailwood's 500 cc RC181 and the tyres are Dunlop, a KR 124 and KR 164.
The machine was ready for 1997 and soon began piling up the victories. Mark had planned to ride the machine himself but was persuaded to let somebody with more experience take on the job.
First man in the saddle was Mitch Boehm, but later in the season Adam Popp took over. Like Mark, Popp is also a resident of Minnesota and turned out to be a godsend, finishing third in the championship despite contesting only half the season on the Honda.
Mark cherishes the memory of Adam's first outing on the CR750 which resulted in victory at Elkhart Lake, Wisconsin.
"I had already seen that Adam had very special talents," he said. "He often led all the classes he entered, but his own machines tended to disintegrate. I felt he should have the chance to try a proper bike.
"Unfortunately, I sent him off without proper instructions, as I forgot to tell him that there was no such thing as idle on the bike. He stalled the engine and got away dead last. I seem to remember that Dave Roper streaked into the lead and built up a huge distance to the rest of the pack, but on the fifth lap a hush went through the crowd as Adam passed him and won."
The Death Wobble
Popp likes the CR750 but doesn't pretend it's perfect:
"In terms of brakes and acceleration, our CR is about on par with a modern 600 but when it comes to road-holding it's a different game. We have strengthened the attachment points for the engine in the frame, but the standard swingarm flexes notably during acceleration out of corners. I call it its 'death wobble' and it is a special problem at Daytona.
"An old chassis like this does not like being turned quickly into corners at high speed. I usually need the whole track to keep speeds up. If I simply throw it into a corner, the front tyre drifts wide. And modern tyres produce more problems...
"I usually hear when the fairing starts scraping and know I cannot lean over any more because the next things to ground are the exhaust pipes. But it's fun when the sparks are flying because whoever is behind me will usually need to back off just that little bit."
Lack of ground clearance forces Adam to hang off the bike, adding another element to his already-spectacular riding style.
"We run Keihin CR carbs and as they have no provision for low-speed running, I have to keep the revs up, especially at the start and in very tight and slow corners," he said. "The engine doesn't come on the cam until 7500 rpm and its performance stays in the high range till 10,000 rpm."
The team managed to find more power for the 1999 season but at the cost of reduced reliability.
Popp said: "The clutch goes first and in '99 we broke two transmission chains. It s a high price to pay, but we still won 11 of the 13 heats we started in and we won the Formula 750 championship for the second year running."
The bike hit 155 mph through the speed trap at Daytona in 1999, a considerable improvement on the 142 mph achieved the previous year, but Adam failed to reach the finish. A visit to the classic meet at Assen ended the same way, but the team has vowed to solve this Achilles heel for the coming season. And you tend to believe these people.
Mark McGrew's M3 Racing company is based in Minnesota, USA. He set up the business specialising in classic racers after a career as parts man with a Honda dealer and ten years as service manager for Honda USA.
A variety of Hondas he and friends own are run under the M3 banner beside the CR750. Stars of the line-up are a 1980 ex-Freddie Spencer RSC1000 and a dirt-tracker once campaigned by Bubba Shobert. The collection also includes a CR450, CR350, CR77, CR93 and C110.
M3 also supplies parts for various Honda racers and prepares engines. Phone or fax: 001-218 937 5166, e-mail: email@example.com. Its website is www.m3racing.com, and you can write them at RR3, Box 176A, Hawley, Minnesota 56549, USA.