Saturday, 27 January 2018

Laverda SF750


I have to admit, before we go any further, that I am a great fan of big vertical twins. Surprising, then, that I was never entirely happy with what in many quarters is regarded as the ultimate in big twin engineering. Part of the problem probably came from the fifty thousand miles that the Laverda had collected in eleven years of loving care and attention. SF owners will have a minor fit if I mention a few of its mechanical foibles that in the final analysis leave the engine inferior in design to the XS650... but using a triplex primary chain to transmit 65hp doesn't inspire confidence - in fact, it inspires snatch at low revs, tensioner disintegration at surprisingly low mileages and an actual primary chain life of as little as 30000 miles. In using horizontally split crankcases, a crankshaft with huge ball bearings, with chain OHC drive from the centre of the crankshaft, there seems little excuse for avoiding the higher machining requirements of using gear primary drive.

Then there's that belt driven dynamo. And lets not forget a ridiculously long stroke and pistons that move in unison. The latter, of course, has always been the major problem with vertical twins. The two huge pistons have no primary balance, and the Laverda relies on massive crankcases and careful balancing of reciprocating components to limit the effects of vibes. This is an improvement on those old British twins and, with the exception of the odd electrical components, the vibration does no harm to engine or chassis. 

Up to 90mph the Laverda is the equal of the Yamaha XS650. At higher speeds the SF is both more powerful and smoother. It is not, however, free of vibration. Owners who equate the feel of the Laverda to the same kind of aliveness exhibited by the likes of a BMW or Guzzi twin have a great art for understatement. Above 5000rpm there is a certain amount of tingling through both footrests and handlebars, that is more pronounced than secondary vibes from a Honda 750 four but nowhere near as bad as a Triumph twin in full, nasty flight. With a few thousand miles use it more or less fades into the background.

The consequence of Laverda ignoring the basic engineering facts of life is that to overcome all this vibration the bike has to be overbuilt in the interests of durability and longevity. Remember, too, that Laverda had little previous experience in motorcycle manufacture, and it seems that they added a little bit more metal than was strictly necessary just to be on the safe side. This all added up to a bike that weighed over 500lbs with a gallon of fuel in the four gallon petrol tank. The major advantage of the vertical twin - light weight and agility - are almost lost amid excessive mass. Fortunately, this is an Italian bike and the effects of too much weight are subdued by high quality suspension and reasonable steering geometry, aided and abetted by decent weight distribution. For most of the time, anyway.

At low speeds the SF feels well balanced and quite easy to flick through the traffic, aided by the relatively narrow profile of the engine. The narrow tank and seat mitigate against the quite high seat height of 32 inches. The petrol tank is quite long, and combined with flat handlebars it's quite a stretch. Fortunately, the footrests are reasonably placed in relation to the handlebars, so that forearms and thighs end up parallel, to give a comfortable riding position at most speeds.

The tubular frame has no down tubes and relies on the engine to acquire sufficient strength. The steering head is well supported by the triangulation of four large diameter, thick steel tubes. The swinging arm is supported by brackets welded onto two of these tubes behind the engine and although this support looks inadequate the bike never twitches about the back wheel, so someone, somewhere must know what they are doing. The steel tube swinging arm would not look out of place on a seventies Jap bike and has the same awkward chain adjusters that make correct wheel alignment a difficult and tiresome chore. Suspension at both ends is provided by the then famous Ceriani outfit. When new this was as stiff as a week old corpse. Fifty thousand miles had helped increase compliance, but neither end could cope with small bumps in the road at low speeds. At least age hadn't left them imprecise or troubled by a lack of damping, as is often the case with year old Jap suspension.

The overall effect of frame and suspension is one of enormous security. The ride of the Laverda is very old fashioned, with more in common with sixties Nortons than eighties Jap high tech wonderbikes. Of course, with its excessive mass the SF can't hope to match the lightness and agility of old British classics, but it has the same kind of high level of feedback from the road and the same kind of feel of running on rails. Pushing the bike through a series of S bends is jolly hard work, but it is never frightening and when the road begins to run out, backing off the throttle doesn't result in any traumatic reactions .

Stability on motorways at high speeds is equally reassuring. Right up to the top speed of 120mph there are never any weaves, and the excess mass can be forgiven, temporarily, as it makes the bike immune to both side winds and the buffeting of speeding, overloaded artics which like to prey on unsuspecting motorcyclists.

It's even possible to hold onto the handlebars at the ton without incurring too much back or arm strain, although the need to glance behind because mirrors end up hopelessly blurred at such speeds means it's quite easy for the wind to catch a full face helmet, trying to snap off the rider's head in the process. In wet weather the Laverda was less than satisfactory. OK,it was a lot more secure than any number of Jap bikes that would lose their back wheel without warning and feel like they were going to lose their minimal adhesion to the tarmac at any moment. But then the SF is a very expensive device and is supposed to be a classic. Running on fairly new Avon Super Venoms there were occasions when the combination of a high centre of gravity and excessive weight would let the back wheel move off line when cornering. There was usually some warning of this activity, but it was often difficult to control because of transmission slop due to the nasty primary drive and a stiff throttle.

A Yamaha XS650 owner would find the Laverda's handling marvellous; a Bonneville or Norton owner would wonder what all the fuss was about; and the owner of a modern Jap four would need a course in muscle building and a bit of psychiatric treatment if he decided to swap bikes.

The original SF had a nicely cast TLS front brake, back in '71. These bikes are very rare, the later SF is a little more common and has twin discs that are powerful, a little lacking in feel, but actually work quite well in the wet. The poor old SF3 was a master of overkill, with a totally silly disc rear brake in place of the better suited SLS drum used by the other models. If the bike is used to the limits of its performance then the twin front discs are definitely needed, although the TLS brake is probably one of the best in the world with a remarkable degree of control - but it is prone to fade when trying to retard 500lbs from 120 mph.

The clutch is heavy but precise, the gearchange was still slick and there was never any hint of missed changes, although it was usually impossible to find neutral from a standstill. Trying to rush changes was not on, but the gearbox didn't seem to object to clutchless changes. Excessive riding in town could cause a little clutch drag, when it was necessary to adjust the clutch at the handlebar lever to gain increased leverage. The riding position and heavy clutch meant that town commuting quickly tired the left hand, but the motor could rumble along in third or fourth at quite low speeds only spoilt by transmission slop. The SF never felt at all relaxed under such circumstances, never settling down into a happy growl until at least 70mph was on the clock.

Fuel consumption was never anything to inspiire the mean or desperately poor. Averaging 45mpg, it would only return 50mpg under the most modest use of the power. Cruising at the ton reduced it to 40mpg, while really thrashing the engine with the rev counter courting mechanical disaster at eight grand used up the gas at 30mpg.

Twin carbs with a surprisingly small bore of 30mm were of a relatively primitive design lacking the sophistication of CV units fitted to the more economical of the Jap twins. Again, excessive mass and silly primary chains can't help the SF to achieve reasonable economy. The cooking version of the engine, in GT750 form, had smaller valves, less radical cams and a lot less power, managing to average a somewhat more reasonable 55mpg.

Riding the SF for a few days through the usual rain and cold would quickly turn chrome and alloy into an horrible mess. The Laverda needs to be cleaned and polished after every ride to keep it in good condition. Paint on the tank and side panel didn't tend to peel off but looked like it had been applied by an apprentice whose skills had been subverted by the fumes given off by paint thinners. The paint on the frame was an altogether different can of worms and usually went AWOL after a mere years exposure to UK weather.

And then there were the handlebar switches that lacked feel when new and couldn't take the wet weather - owners of twenty year old Hondas would be shocked by the lack of quality... long term owners will have dumped the switches, resprayed the cycle parts and taken out shares in Solvol, so these aren't really relevant complaints. But, oh dear, that quaint Bosch dynamo and associated regulator would make a Morris Minor owner go all misty eyed. Electrical integrity is especially important because Laverda were ahead of even the Japs in dumping the kickstart and this kid, for one, would not even dream of trying to bump start 500lbs of top heavy Italian exotica. Some dynamos are in trouble by 20000 miles, so prospective purchasers should ride everywhere with full beam switched on to check out that some kind of power is actually being generated. On very cold mornings it's often necessary to jump lead to a car battery to get the starter enough power to overcome the drag of the cold oil.

The crankshaft is very tough, the carefully selected pistons and high quality bore job means rebores can take as long as 75000 miles before they are needed, the valvegear is surprisingly resistant to bounce (given the size of the valves) and even the camchain and tensioner can make it past fifty grand without needing replacement . At least the small end plain bearings and roller big ends are relatively easy to replace and don't mean a new crank is needed as is so often the case with Jap bikes. The engine has obviously been built out of high grade materials with long life and ease of maintenance firmly in mind. Rear tyres are down to 2mm in as little as 7000 miles, while the front can go for as much as ten grand.

Riding on worn tyres doesn't cause too many problems in the dry but definitely aint recommended in wet weather. Chains last anywhere between five and ten grand, depending on maintenance and power usage. Disc pads last for six to eight grand and the rear drum shoes can make it all the way to twenty grand.

The modern Jap multis make the SF seem very, well, old. In an era when Jap bikes handled so badly the SF was a welcome relief, but the basic flaw in its design of excessive mass now make it little more than a curiosity piece. Yeah sure, it looks so right, so brutal and effective, that it's easy to be taken in and write pages of creepy prose to the effect of what a wonderful piece of classic machinery it represents. But its engine doesn't last any longer than an XS650 and its performance is no better than a good 550. If we were talking reasonable money, say £300 to £500, then the SF might have a lot going for it. At present prices leave it to the Sunday afternoon brigade who know no better...

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