Honda V45 Magna

HONDA V45 MAGNA

CYCLE WORLD TEST

Honda Reinvents the V-Four; Discovers Torque and Compliments Willie G.

Engines. Year in, year out, stepthrough to world championship, if there’s one thing Honda is most famous for, it’s got to be engines. All types and sizes and kinds, from the old reliable to designs everybody else has forgotten to configurations never before considered, what Honda does best is make engines.

Here we go again, in the lightweight, lumpy and delightful form of the V45, 90° V-Four, 750cc with double overhead camshafts, four valves per cylinder, and water cooling. For 1982 Honda offers the V45—the name for an engine remember, ¡*ot for a motorcycle—installed in the Magna and the Sabre.

As the pictures make perfectly clear, the Magna is a Custom. American style, the Honda reps say, the Magna was designed as an extension of the Custom look, with shaft drive because dealers say their customers like and demand shaft drive, and in high performance form because the other factories (in particular Yamaha) don’t have high performance versions of the Custom/Special/LTD/ Low Slinger theme.

The V45 is a fascinating, complicated, wonderful engine. But before getting into details, note that this configuration is readily adaptable. For a 750cc Four, it’s narrow and low and light. In the case of the Magna, this means the seat can be low and the pegs can be set forward, for the laid-back, semi-Harley look on which the soft-core chopper look is based. In the case of the sporting Sabre, the same configuration can allow a lower engine for a lower center of gravity, better cornering clearance, etc.

Next, the use of the Vee. In the Sixties Honda worked on inline engines, mounted across the frame. There were Twins, Fours and Sixes, even one Five. Most of these racing designs later appeared in production. Back in R&D the thinkers were investigating the Vee, as seen in the CX500, then the Grand Prix NR500, the Formula Two car V-Six, which is three CX500s in a line, with twin-cam heads. In recent months there’s been the V-Triple two-stroke GP NS500 and the V45-based V-Four Formula One racer. What next? All we have in hints: “There are lots of uses in mind,” one Honda rep said, “You’ve only seen two.”

So. The V45 has two banks of cylinders, separated by 90°. Nestled within the Vee are four CV carburetors. The front exhaust pipes run forward and down, the rear ones snake down, back and out. (Rear exhaust ports are bad news with an air-cooled engine, no big thing with water cooling.)

The V45 can be considered as two tiny V-Twins side by side, or as two tiny Vertical Twins 90° apart. The crankshaft has

two throws, in the same plane and each throw carries two connecting rods. The two pistons in the forward bank go up and down together, and so do the pistons in the rear bank. But when the front left piston is on the power stroke, the right front piston is on the intake stroke and so forth. The left-right firing order is one revolution apart while the front-back is separated by one revolution plus or minus the 90°. There is a staggered pulse and a staggered exhaust note, somewhere between the parallel Twin and the V-Twin.

Crankshaft rotation is backwards, that is the engine rotates opposite the direction of the motorcycle’s wheels. This enables Honda to use the most direct power transmission, with the gear driven primary and no auxilliary shafts in the transmission. It’s also possible to achieve the same thing by extending the middle gearcase shaft forward and driving the bevel gear from the forward side of the countershaft gear, but this is Honda’s way and it works.

The crankcases split horizontally and the cylinders are an integral part of the upper case, the liners being cast-in and

surrounded by water jackets. A double overhead camshaft cylinder head bolts to each bank of cylinders.

The engine is radically oversquare, having 70mm bore and 48.6mm stroke, and uses flat-domed cast pistons and small, relatively-flat combustion chambers with swirl-inducing ridges cast into the squish area. Each combustion chamber has four valves, two 26mm intakes and two 23mm exhausts. The valves are operated by forked rockers, one cam lobe opening each set of two intake or exhaust valves, and valve lash is adjusted with conventional screw tappets.

Each set of cams is turned by a single link-plate chain running in a loop from the center of the crankshaft, and each chain is almost completely surrounded by guides and shoes and is held in proper adjustment by an automatic tensioner positioned inside the loop. Cam timing measured from and to 1 mm lift opens the intake valves 5° BTDC and closes them 40° ABDC; the exhaust valves open 40° BBDC and close 5° ATDC. Intake lift is 8mm, exhaust lift also 8mm.

It’s a 90° V because that angle yields perfect primary balance and also leaves enough room in the center for a sophisticated set of carburetors similar to those

developed for the Honda NR500 Grand Prix racebike.

There are connections to the NR project. The engineers working on the V45 engine wanted a narrow valve angle and big bore so the combustion chamber could be kept small and flat and shaped just right to improve burn characteristics, avoid shrouding the large valves needed for good breathing, and produce a high compression ratio without a highdomed, flow-interrupting piston.

But narrow valve angles combined with dohc produce tall cylinder heads, and the engineers wanted the engine to be as compact as possible. The solution was to use screw-tappet rocker arms positioned below and to one side of the cams, in the process making valve adjustment easier.

So the Honda V45 has a 38° included valve angle and a very flat combustion chamber, reducing the distance the flame front must travel from the centrally-located spark plug, and so discouraging detonation. To remove excess heat from the combustion chamber—and further discourage detonation—coolant passageways run between the valves and the spark plug. The end result is that the V45A has a high 10.5:1 c.r. and can run without detonation on any gasoline with a pump octane rating of at least 86.

(Tor comparison, the air-cooled dohc CB750 Four has a 63 ° included valve angle, 9:1 c.r. and pings on premium 92 octane gasoline).

To reduce friction, the pistons have very thin compression rings, 1,2mm each. The three-piece oil control ring is 2.4mm thick when assembled.

Less obvious, but still interesting, is the ratio of connecting rod length to stroke. While the V45 has a short stroke (48.6mm), it has unusually long, connecting rods, 1 17mm measured center-to-center, producing a rod-to-stroke ratio o. 2.4:1.

One of the more durable misconceptions in motorcycling is that a long stroke engine produces more low-end torque. If that were the case, the 62 x 62mm Honda dohc CB750 Four engine would produce more torque at a lower rpm than the V45t But that isn't the case, and riding the two bikes back-to-back illustrates that very dramatically. The V45 has an excellent powerband; the CB750F does not. The difference is in the rod-to-stroke, the CB750F’s ratio is 1.8:1. The Kawasaki KZ750 has a superior ratio of 1.94:1 with a stroke of 54mm and 105mm rods, and the Suzuki GS750 has an even better ratio of 1.98:1 with a 53mm stroke and 105mm rods. Both the Kawasaki and the Suzuki have shorter strokes yet better powerbands than the CB750F.

Of course, other things must be consi<^¡¡ ered, such as valve area, cam timing and lift, compression, etc. But all other things being equal, a connecting rod that is

longer in relationship to stroke will increase torque at a given engine speed.

The horizontally-split crankcases allow the cylinders to be integral parts of the upper case half. But power pulses from the forward, inclined toward-horizontal cylinders increase sheer loading along the case split and on the crankcase bolts. So the cases are held together around the crankshaft by 16 bolts instead of the more normal eight bolts, with two bolts on each side of each main bearing. The bolts are special, too, with beefed-up shoulders that fit very tightly in the case holes, reducing possible movement at the joint.

In early tests Honda engineers found a tendency for the high compression ratio of the V45 engine to cause piston deformation through wrist pin flex. To avoid the problem the piston wrist pin hole is now oval, being 15-20 microns wider on the axis perpendicular to the stroke. The slight oval hole shape gives the pin room to flex without deforming the piston.

The power train is straightforward and simple. Primary drive is straight-cut gear to the clutch basket. The hub of the 11plate (six friction, five steel) wet clutch rides on the mainshaft, which drives the countershaft through the six-speed transmission. A bevel gear on the end of the countershaft powers the final driveshaft, (which incorporates a ramp-and-cam damper.)

The anti-lash clutch basket gear is in fact two thin gears, both straight-cut, with slightly offset clutch damping spring

cutouts. When the gears are stacked together and assembled to the clutch basket, the damping springs offset the teeth slightly. That bit of spring-loaded offset takes up slack between the teeth of the crankshaft gear and the clutch gears, preventing gear rattle when the bike is in neutral.

The clutch is hydraulically controlled, a master cylinder on the handlebars operating a slave cylinder piston pushing a rod through the mainshaft to the pressure plate. The clutch basket rides on needle roller bearings when disengaged.

The transmission has six speeds. Honda calls sixth gear an overdrive and when the bike is shifted into sixth a little blue panel light, labeled OD, comes on. In reality, an overdrive is a separate gearbox attached to the transmission, and what the Honda has is a six-speed transmission.

The jump between fifth and sixth isn’t especially great. Compare the V45’s first five overall gear ratios to the five speeds found in the CB750F Four and they’re almost identical. The CB750 has ratios of 15.27, 10.78, 8.39, 6.99 and 5.81:1 for first through fifth, respectively. The Magna’s ratios are 15.06, 10.63, 8.48, 7.05, and 5.89 for first through fifth, with sixth being 4.92:1. That’s about the same percentage change between fifth and sixth as between fourth and fifth.

Besides having more gears, the Magna has those gears shimmed closer togetherthan-normal with machined engagement dogs. Most Hondas have 1.5mm mini-

mum gear spacing, with gear engagement dogs forged and left as is. The Magna gears are 1.0mm apart when engaged, increasing dog penetration, and the gear dogs are longer when forged then machined down so the corners are square. Both changes are designed to improve shifting and avoid problems with the transmission popping out of gear under hard acceleration.

A small sprocket attached to the back of the clutch basket drives an auxiliary shaft by a roller chain. The oil pump is mounted on the auxiliary shaft and drives the water pump through a coupling.

The oil pump pressure feeds all the shafts in the engine plus the rocker arms and transmission shift forks. Oil is routed to the valve train through external metal lines. An automotive-type, spin-on oil filter is nestled next to the electric starter on the front of the lower case, hidden between the front exhaust pipes.

The water pump circulates coolant through the engine and to and from the radiator. Honda engineers made an effort to minimize external plumbing and to make the engine look as “normal” as possible, and it shows. Each cylinder head sports fins for styling—they’re not needed for cooling—because most motorcycles have cooling fins. Water from the radiator reaches the pump (located underneath the countershaft cover) through the removeable left front downtube. From the pump a chrome-plated metal tube takes the water up around the alternator cover (on the left end of the >

crankshaft), to crankcase fittings between the cylinders. Internal water jackets surround the cylinders and passageways run through the heads. Coolant exiting the front cylinder head is routed through a metal pipe and a rubber hose to another pipe draining the rear cylinder head. From there another rubber hose (like the first, wrapped in a spring wire cover) carries the coolant through the cast aluminum airbox base to the radiator, being partially hidden in its travels by the chrome-plated airbox sidecover.

Four 32mm Keihin CV carburetors bolt directly to the airbox, forming a massive assembly. However the carburetor and airbox assembly weighs 1.4 lb. less than the bank of four carburetors and brackets on the inline Four Honda 750.

Honda’s literature calls the carburetors on the V45 sidedraft-downdraft, referring to the direction of air flow through the venturi. Sidedraft carbs have been standard on virtually all motorcycles for a number of years, mostly because they worked well on the vertical cylinders that became normal, though some bikes with horizontal cylinders, such as the forward cylinder of a Ducati, or the cylinders of a Gold Wing use sidedraft carbs with bent

intakes because only sidedraft carbs were available in the right sizes.

That’s changing with more alternate engine configurations developing and it’s a good thing because carburetors that can flow air directly into intake ports provide less restriction to air flow. That’s why the V-Four Honda uses a mix of carb shapes. For the front cylinders the barrels are vertical, wath the float bowls beside the barrels for level operation. The back cylinders get carbs that aren't quite sidedraft or downdraft, being more of a diagonal draft, again with the level float bowls beside the barrels. Fuel passageways and jets are angled inside the float bowls to prevent fuel starvation under hard acceleration or deceleration. And being CV carbs. there is a butterfly throttle controlling intake vacuum, and the intake vacuum controlling the diaphragm that lifts the needle and piston.

A pleated paper air filter fits atop the carbs in the airbox, under the gas tank, between the top frame rails.

Ignition is transistorized, with electronic advance and the pickups on the right end of the crankshaft bathed in oil. There is no timing adjustment possible, so any problem will require parts replacement.

The chassis looks conventional enough, with two backbone rails and dual down-

tube engine cradle. But a large section of left downtube unbolts to make engine removal easier, and that same section carries water from the radiator to the pump as well.

To reduce weight, the frame is made of thin-wall tubing with a higher tensile strength than the thicker wall tubing used on some other Honda models. The new tubing has walls 1.4mm thick; the old stuff’s walls are 1.6mm thick. The weight saving is 16 percent, but using the thinner wall tubing requires more precise joints and more accurate welding of those joints, with less filler.

The engine is secured to the frame bythree sets of rubber mounts; one set at the front of the engine cases, another at the bottom rear of the cases, yet another at the back of the rear cylinder head. Because it’s rubber mounted, the engine cannot be used as a brace between frame members. So a tube is welded between the members at or near each set of engine mounts, to improve chassis rigidity.

Rubber engine mounts absorb almost all of the high frequency, secondary vibration produced by the engine. Because the shaft drive maintains correct alignment with the rear tire, the V45 doesn’t need the locating link used on the CB900F Honda, so normal rubber bushings are all that are required.

Swing arm and steering head bearings are tapered roller. The leading axle forks have low friction bushings, two to a side, with both bushings fixed in the fork stancion tube. On older Hondas one bushing rode in the stanchion tube and the other in the slider, so the distance between the bushings changed as the fork compressed rand extended. Now the bushings remain at a constant distance, reducing fork binding.

The forks have the type of anti-dive systems first seen last year at Laguna Seca on the NR500. Mounted on the left fork slider, the system restricts the flow of ’-damping oil by rerouting it through an external, variable-orifice passageway when the brakes are applied. By restricting oil flow, compression damping is increased and the rate of fork compression reduced.

The system differs from the anti-dives viseen on some Suzukis and Yamahas in that it is activated mechanically, not hydraulically off the brake lines. When the brakes on the Honda are applied, the caliper grips the disc and pivots inward on its upper mount, pushing in a springloaded piston which diverts the oil. The ^harder the rider applies the brakes, the harder the caliper pushes against the spring-loaded piston on the outside. Applying more brake increases the weight

transfer trying to compress the forks, and the damping oil pushes harder against the piston on the inside. It’s a carefully calculated balance, and anything that upsets that balance—like a bump encountered in the pavement during hard braking—tips the balance to the inside, forcing the piston momentarily off its seat, allowing the forks to respond before the spring reinstates the piston and continues the oil diversion.

The rate of fork compression for a given braking force can be altered by changing the size of the orifice through which fork oil is diverted when the brakes are applied. Orifice size is selected by a screw on the side of the fork leg, which has four spring-detent-located positions, labled soft, standard, firm and extra firm.

The anti-dive system is built into the left slider only. Honda engineers say that the benefits gained by using the system on both sliders would be offset by increased cost and weight, and that the substantial cast alloy fork brace installed between the sliders, above the fender, prevents problems with fork torque or twist. At any rate, we did most of our riding with the anti-dive set at the extra firm position and loved it. It works, and because it’s mechanical, doesn’t take away any power or feel from the brake system.

For a variety of reasons the Magna doesn’t get the single shock Pro-Link rear suspension used on the Sabre. Where the Sabre has a large single spring and shock, the Magna has a second gas tank. And the Magna gets to show off a pair of chrome-plated shocks that look more like a Harley shock than anything else. The collars with little holes at both ends, and

the huge top shock eye are right out of Milwaukee. Of course Honda has to improve on anything, so the Magna’s shocks get reservoirs fastened to the lower end of the shocks. The only adjustment provided is preload.

At the bottom of the shocks is a swing arm unlike any other Honda swing arm. This one has the driveshaft on the lefthand side, and uses a boxed steel leg on the right. All previous Honda shaft drive bikes have had the final drive on the right, which is why Honda added a twospeed subtransmission and additional crossover shaft on the CB900 Custom, Honda explained. Along with the new final drive the Magna has a long swing arm to reduce driveshaft induced torque reaction. Add a long swing arm to an engine that’s 24.4 in. long from the front of the forward cylinder head to the back of the engine cases (a CB750F engine is 21.2 in. long) and the result is a 60.6 in. wheelbase.

The Magna is long, but not overweight. With half a tank of gas, it weighed in at 518 lb. That’s competitive, considering that the CB750F weighs 544 lb., the Suzuki GS750 550 lb., but not as light as the Yamaha Seca 750 (503 lb.), the Kawasaki GPz750 (506 lb.) or the Kawasaki KZ750 (491 lb.).

The Magna comes with cast wheels, an 18-in. front and 16-in. rear. Cast wheels on Hondas are new. Until this year the company used ComStars, composite wheels made with alloy rims and hubs and large, flat steel or alloy spokes, the whole lot held together by special bolts. ComStars, according to the official line, eliminated worries about porous castings deflating tubeless tires, and improved >

ride and handling by incorporating just the right amount of flex. The Magna comes with cast wheels for styling reasons and because surveys showed that many people prefer cast wheels. Each wheel is pressure-checked for porosity before being installed.

The tires, a Dunlop 110/90-1 8F1 1 front and 130/90-16 K127C rear, have raised white letters and feature, according to Honda spokesmen, a deeper tread with no center groove and a harder compound for long wear.

Brakes are two 10.8-in. discs up front and a 6.25-in. drum in the rear. Each side of each disc has six grooves cut in at an angle. Grooves in discs first showed up on racebikes. According to racing theory, grooves carry off water to improve wet braking, reduce disc scarring by collecting grit and dirt that would otherwise become imbedded in the pads, and remove glaze from the pads. Some motorcycle engineers dismiss the theories and say the grooves are only cosmetic.

Whatever the case, the Honda’s brakes are tremendous. The dogleg lever is within easy reach of the handlebar grip, and braking action is progressive and predictable.

And strong. The Magna stopped from 60 mph in less distance than any other 750 recently tested, 125 ft. (Other 750s include the GPz750, 131 ft.; the Honda CB750F, 139 Ft.; the Yamaha Seca 750, 130 ft.). Some of the credit must go to the anti-dive system, but that doesn’t change the results.

The engine is just as brilliant, delivering strong power from just above idle to well beyond the 10,000 rpm redline. This is the first Honda Four with mid-range power, and it comes off corners as hard as anything in its class.

The mid-range makes the Magna perfect for cutting through city traffic, because there’s always power at hand when an opening appears. The tall sixth gear lets the Magna lope along at less than 4100 rpm at 60 mph. Most 750s run about 4500 rpm at 60.

And the Magna screams at the dragstrip, leaving hard and pulling hard to stop the lights at 12.06 sec. and 108.82 mph, still revving with the tach showing 11,000 rpm in fourth. The combination of a wide rear tire, excellent torque and high peak horsepower make the Magna the second-quickest 750 ever tested by this magazine. In the half-mile top speed test, the Magna ran 122 mph, not bad for a bike with bucko bars and a frontal-areaincreasing radiator.

Then there’s the exhaust note. It’s a different sound than that made by an inline Four, throatier, slightly uneven, exciting. The Magna sounds neat.

Despite the tall top gear and good midrange power, the bike doesn’t set any mileage records. It recorded 46 mpg on the mileage loop, a mix of city and highway riding. That’s comparable to the 45 mpg of the Kawasaki 750, but not up to the 55 mpg of the Yamaha Seca 750, or the 51.5 mpg of the Suzuki 750.

On the street at almost legal speeds, the Magna maneuvers and handles well. Driveshaft jacking is noticeable if you look for it or are clumsy with the throttle, but otherwise isn’t intrusive. Up the ante and head through a stretch of curvy pavement at speed and the bike’s limits show up at once. The footpegs, being forward and spread wide around the engine, drag early and the long wheelbase demands lots of lean for fast cornering.

The Magna doesn’t like abrupt changes. It will fly through fast corners and remain steady and sure as long as the throttle is held steady from entrance to

exit or the bike is accelerated through. But change the loading on the chassis by closing the throttle or hitting a bump and the bike pitches back on the shocks and the bars start a slow, damped oscillation.

With fork air pressure set at 10 psi and the rear shocks set at #2 preload, the wobbling and scraping (with a 150-lb. rider) through sweeping turns is substan-'1 tial. Increasing fork pressure to 20 psi and setting shock preload up to the #4 position makes about a 200 percent improvement, with more cornering clearance and less pitching and wobbling midturn. Abrupt changes with the throttle still start the bars waggling, but with less* force and less frequency. At those settings the Magna can actually be ridden through corners fairly rapidly. It doesn’t wobble in a straight line.

Cornering clearance limits lean angle enough that the tire tread edges aren’t used. Even so, dialing on more throttle^ with the pegs (and rear brake lever and sidestand foot, on the right and left, respectively) already scraping will make the rear tire start to slide. In other situations the tires have good adhesion and cause no problems when properly inflated. J,

These are big tires, wider and smaller in diameter than those on most bikes this size. Honda has been using more 18-in. front tires this year, with wide rims and wide profiles. Besides keeping the height

of the bike low, the big front tire is not easily turned at low speeds. Until a rider adapts to the Magna, the front end wants to run wide. This is a slow steering motorcycle.

Some of the steering and control sensations are due to the handlebars. The Magna’s handlebars aren’t any wider than normal, and they aren’t higher off the ground than many normal bars are, but they have exaggerated pullback. From the triple clamp they begin farther back than normal because of the offset handlebar pedestals. Then the bars extend another foot back. The result is that the end of the handlebar is only about 8 in. ahead of the front of the seat, which is about twice as close to the rider as a normal motorcycle.

This abnormality puts the rider in a position that would be about right if he were carrying a typewriter, but for controlling a motorcycle it is odd. Even Harleys like the Low Rider don’t have such extreme pullback, plus a Low Rider has a 65-in. wheelbase stretching things out more.

What the Magna uses for comfort is a soft suspension and a relatively soft seat. With little air in the forks the Magna’s suspension is plush. A Lincoln couldn’t absorb bumps any better. The seat is also soft, Honda not going for an ultra-low seat height, but for adequate padding on the 30 in. high seat.

At the back of the raised passenger portion of the seat is a small box and a short sissy bar. It resembles the stash pouch on the back of a Harley Low Rider, but it contains tools and doesn’t have room for any stash. The sissy bar was soon known as a shin-kicker because it made throwing a leg over the seat painful for the unwary.

Vibration is about on a par with that of the Gold Wing, or about as controlled as it gets. There isn’t any speed where the bike vibrates more or less, being smooth at all speeds. It is also spared the high frequency tingling that aflicts so many Fours, thanks to the rubber mounts.

Controls and instruments on the Magna are very good. Clutch pull, throttle spring tension and brake effort are pleasantly low. Clutch feel isn’t as direct, what with the hydraulic coupling, but the ample torque of the engine makes it simple to ride. Clean, round speedometer and tach dials are easy to read, though the needle on the tach could be made to jump around madly by short shifting and holding the throttle open wide. The choke is conveniently located at the inside edge of the left handgrip cluster, though it doesn’t require much attention because the Magna runs so well hot or cold. Warning lights for neutral, high beam, oil pressure, taillight failure, low fuel, and top gear are so dim that they aren’t easily visible during the day, but at night they

are nicely subdued.

Beneath the various lights is a rubber blob that clips over the center of the handlebars. Things like that and the chromeplated plastic end caps on the fork tubes make the Magna seem over-styled to our eyes. But any skepticism about the styling is overwhelmed by the outstanding V45 engine. It makes excellent horsepower (80.3 bhp at 9500 rpm), it bristles with internal combustion technology and dazzles the senses with its all-around performance.

There’s also more power inside the Magna’s engine, judging by the size of the ports and the mass surrounding the ports, waiting for the tuner’s porting tool. The racing versions of this engine are liable to be very fast motorcycles.

This is a high performance custom. At the same time the Kawasaki GPz750 develops 80 bhp with an inline, two-valve, air-cooled Four, and Honda’s own CB750F has 75 bhp. The V45 doesn’t have all that work and all those features and complications merely to produce another five bhp. If Honda just wanted more power, they’d could get it from the CB750, never mind the newer engine. The V45 Magna is merely the first application for some systems and ideas Honda is developing.

What we have in the V45 Magna is a wonderful engine, an acceptable motorcycle and a hint of more marvels tocome.H

HONDA

V45 MAGNA

$3298