SURPRISE-WORLDS LARGEST MORINI

CENTRE IS IN LEICESTERSHIRE  UK

Tucked away in Ellistown in an old two storey building is the long established Company, North Leicester Motorcycles. Beating a path to their door are people from all over the world. Moto Morini motorcycles and spares are the cause and certainly this eccentric shop is seething with Moto Morinis, mainly from the 1970~85 period. Already accepted as a classic, these motorcycles are owned by many different types of people for all possible uses. Daily work runs, Sunday afternoon blasts, African safaris, posing, a run from Alaska to Mexico have all been enjoyed on this reliable and delightful middleweight.                                                                                                        

For those not sure of the technicalities the bikes major forte` is its superb roadholding, the engineering is simple but beautifully designed and executed in top quality material. The bikes were way ahead of their time, always fun but oil tight and modern. Mostly 350cc, a few 500cc and 250cc,always V twin 4 strokes with advanced features only now being adopted by some others. Morini have always offered a Heron head, that is combustion chamber in the piston, dry clutch, electronic ignition, still air box to aid carburation, low centre of gravity and many more features which other manufacturers are proud to claim as fresh on some of today's modern motorcycles.                                                      

Terrific economy,and what Morini owners refer to as "the highest possible grin factor" continue to make the bike so much safe fun that it hardly seems important to owners that Morinis are appreciating probably faster than money left in the building society. Even the weather is on our side this year,Moto Morini really are enjoyable and there is a good interesting choice of models at North Leicester Motorcycles.

An article written by the Leicester Gazette.

Recommended reading and an excellent gift "MORINI"  by Mick Walker.This is available from us at £14.95                                                                                                                                           

OUT OF THE RUT !
Technical Editor Vic Willoughby explains the advanced design features, that enable Moto-Morini to combine punch, revs, smoothness and economy in their 350 cc engine.

Moto Morini call their 350 cc six-speed Vee twin simply, the 3 1/2.Yet there is no machine more captivating, either in it's Strada (Street) or Sport guise. A treat to the eye in unmistakably Italian style, it is compact, light and a joy to handle.

As smooth as oiled silk, the engine is both free-revving and punchy. What's more it is easy on the ears and the pocket alike. Yet the cooking version will whisk you up to 95 mph, while the sports version will smartly top a ton.

This charming combination of qualities is no accident. It is a result of Italian design at its best - sound and advanced, yet imaginative and artistic too.

Indeed, so advanced is the Morini that it is unique among motor cycles in having so-called Heron cylinder heads. These have a flat face (hence parallel valves) with the combustion recess formed in the piston crown.

Other features that help lift the engine out of the rut are a toothed belt to drive the camshaft, extensive use of beautiful pressure diecastings, a forged one-piece crankshaft, transistorised ignition and highly developed porting.

Since production is on a small scale (about 3,000 a year at present) great pains have been taken to keep down production costs. For example, the pistons, cylinders, heads, connecting rods and several other parts are identical.

Indeed, many of the three-fifty's engine parts are common to the 125 cc single already in production (front cylinder only) - and precious few changes are envisaged for the electric-start 500 cc twin, soon to be launched.
                                                

CHARACTER

The Morini vee-twin was born in 1971. Why did designers Gino Marchesini and the younger Franco Lambertini choose a 72-degree cylinder angle and Heron heads?

"We wanted a quality product with more character than a parallel twin," they say, "and a vee-twin is extraordinarily smooth running. Our 72-degree angle is a compromise. It is very little less silky than the ideal 90-degrees and has slightly more even-firing intervals."

"The angle is narrow enough for compact installation in our race-bred frame and wide enough for the camshaft to be mounted high in the vee of the crankcase."

"Even so, to make room for the camshaft we've had to space the cylinders apart slightly, giving a double desaxe effect. This means that the cylinder halves don't intersect at the crankshaft centre line but slightly below it.

"Naturally, this alters the firing intervals marginally from the nominal 432 and 288 degrees. If you really want to know, the longer interval is 433 degrees 19.14 minutes, and the shorter one 286 degrees 40.46 minutes!"

"We chose Heron heads chiefly because they are cheaper to produce - the underside is planed flat, not spheroid. But there are technical advantages too, in fuel economy and high torque, which we think we have exploited more than anyone else."

In the car world, Heron heads have an impressive pedigree. They were used in the Repco Brabham that won the Formula 1 world championship in 1966. You will find them on the Jaguar V12, the Rover 2200, the Alfasud and some Fords and Audis.

Traditionally, high performance from two-valve heads has long been associated with part-spherical combustion chambers in which large valves can be accommodated. Parallel valves have to be smaller in diameter and before the advent of the Heron head, generally came to be associated with lower performance.

If, for example, the head face and piston crown were both flat, then the combustion chamber was a horrid pancake shape, with high surface/volume ratio and long flame travel, and the compression ratio was low.

Alternatively, concentrating the combustion chamber and so raising compression - by using a squish head form with a flat-top piston - entailed putting the valve heads in some form of "inverted bath tub" which masked their opening.

The Heron head sweeps round both these drawbacks. By bringing the piston crown close to the flat head face all round the valve heads and sparking plug, the combustion chamber is concentrated and a high compression ratio is achieved. Yet the valve heads are completely unmasked once the piston moves down from top dead centre.

This lack of masking and the fact that the business ends of the ports are more nearly parallel to the valve stems, means that much more of the valve periphery is used than in a crossflow head, where little more than half of it may be effective.

"We have made an exhaustive study of porting and combustion in Heron heads," Lambertini told me. In fact, Morini were already past masters in this field, even with conventional heads. For the 250 cc racing single on which Tarquinio Provini led the Honda fours such a dance some years ago (and on which Giacomo Agostini first shot to fame) had a phenomenal brake mean effective pressure of 206 psi at 10,500 rpm.

That's the average pressure on this piston crown, net of mechanical and pumping losses, throughout a complete cycle. And if the figure means little to you let me say that even today, a dozen or more years later, it is comparable with the best in Formula 1 car racing.

Morini's porting research on the 3 1/2 shows most clearly in the peculiar shape and pronounced taper of the exhaust port, the small diameter of the exhaust valve and the uncommonly large (gradual) underhead radius on both valves.

"The small exhaust valve is fantastic for torque," says Lambertini. "The curved port opens out from 18.5mm at the throat to 25mm at the outlet. As a result, gas speed through the throat is very high and we get a deep depression there during valve overlap."

"In conjunction with the ram effect of the inlet tract (which narrows from 25mm in the carburettor to 23.5mm, then opens out to 26mm at the throat) this gives us extremely good cylinder filling, even at low revs, while the port layouts minimise any loss of fresh charge to the exhaust."

Lambertini's claims are backed up by a specific fuel consumption of 0.43 to 0.46 lb/bhp/hr, which is very low. Incidentally, the large radius between the valve stem and head is dictated by the high gas speed.

But it isn't the porting alone that accounts for the combination of high torque and low petrol consumption. Other contributory factors are the high compression (with low surface/volume ratio) and the unusual combustion pattern.

Let's look at compression first. There are three levels to the piston crown. The top level which surrounds the valve heads and sparking plug, has a new moon shape adjacent to the plug and a peaked shape opposite.

It is the height of this level that determines the squish clearance and compression ratio. In the Strada the clearance (from the cylinder head) is 3mm, giving a compression of 10 to 1. In the Sport the clearance is only 2mm and the compression 11 to 1.

The next level (2mm lower on the Strada, 3mm on the Sport) is kidney shaped under the valve heads. A further 2mm down, the bottom level is circular, not quite in the middle of the crown.

Now for the ingenious combustion pattern. As the flame front radiates out from the plug points (like ripples on a pond) maximum pressure occurs at the point of the peak on the opposite side.

This splits the flame fronts into two vortices, which rotate outwards and back towards the end of the advancing front.

Compared with conventional pistons, those in a Heron layout run hotter because there is more crown area exposed to heat. "For that reason says Lambertini, "our piston skirts are split so that they can expand circumferentially and don't need excessive running clearances. Also there is plenty of metal in the crown for a heat sink, and an ample path down to the ring grooves."

Moving the cylinders apart (desaxe) naturally alters the leverage of the connecting rods - and in opposite directions.

"To restore the leverage to normal," says Lambertini, "we offset the gudgeon-pin bosses inward slightly in the pistons. In the front cylinder however, the net result is for a slight tendency for the piston to rattle because of the increased slap at tdc."

"We counteract this by reducing the radial depth of the slotted oil scraper sufficiently to put a to put a thin expander spring behind it."

Since the crankshaft is a one-piece forging, the steel con-rods are split across the big-end eye. Running two rods side by side on a common crank-pin normally offsets the cylinders by the width of a big-end eye.

In the Morini this stagger is increased to 30mm by the fact that the shanks of the rods are also off-set relative to the eyes. The stagger moves both exhaust ports out into the breeze.

The crankshaft is located laterally by a large ball bearing on the drive side (left). Unusually however, crankcase expansion is not catered for by a roller bearing on the other side. Instead a smaller ball bearing on the right is a sliding fit on a crankshaft sleeve.

Thought the crank cheeks are formed into bobweights for balance purposes, there is no flywheel.

Lambertini explained: "A vee-twin has less need of a flywheel than other layouts because both pistons aren't at rest at the same time. When one is stationary at tdc the other is travelling at full speed, so acting as a flywheel."

"In any case the aluminium alternator motor on the right has a hefty steel rim. On the five-hundred twin, teeth will be cut on this rim for the drive from the electric starter."

Clamped against the left-hand main bearing is the helical gear for the primary drive (ratio 29:66) and outboard of that, the worm that drives the half-speed oil pump.

Outside the other main bearing (and protected by an oil seal on the crank-shaft sleeve) is the steel pulley for the camshaft drive belt. The combination of eight keyways and eleven teeth provides a fine vernier adjustment for the valve timing.

There is no provision for adjusting the belt (periodic renewal is recommended) and the 22-tooth pulley on the camshaft is made of cast iron "Its weight stabilises the rotation of the shaft," Lambertini explained,"and so prevents belt snatch."

Two ball bearings support the camshaft, and the four flat-base steel followers run direct in the aluminium crankcase - a compatible bearing combination.

Anyway, the followers have a large bearing surface and are slightly offset to the cams so that they rotate in use, and the cups for the steel ball-ends at the bottom of the solid duralumin pushrods are right down in the base of the followers to minimise side thrust.

Tunnels for the short pushrods are cast in the cylinders and heads and steel cups at the top of the rods engage adjustable ball-ends on the rockers.

Slim and straight, with a continuous shank above the boss, these combine light weight with great stiffness and make line (not point) contact with the valve tips.

A leverage ratio in the rockers multiplies the cam lift by 1.375 at the valve - that is, 7mm of cam lift on the Sport gives more than 9.5mm of valve lift. The shorter travel of the cam followers and push rods eases the problem of controlling the valve gear at high revs, so pushing the valve float beyond 9,200 rpm, even with comparatively light springs.

Oiling the gear cluster by splash from the engine is established Italian practice, and so is a gravity return to the integral sump. But there is a further simplification on the Moto Morini is that oil is fed only into the crankshaft.

Crankcase pressure is relied on to force oil mist up the push rod tunnels to the over head valve gear, and there is a groove round the middle of each valve stem for oil retention.

In the breather in each rocker cover is a conical oil separator with 7 staggered baffles - and there are two such separators in the large bore plastic breather leading from the rear of the gear compartment.

Powered by the alternator (so that the battery may be removed for racing) the transistorised capacitor - discharge ignition is supplied by Ducati- Elettrotecnic. The rotor is on the left hand end of the cam shaft and the stator mounting is slotted for timing adjustment auto-advance is electronic, ranging from 10 degrees static to 34 degrees at 6,000 rpm then backing off to 30 degrees at 10,000 rpm - though it is arguable whether that slight retarding is from choice or necessity. Of the 2 high tension coils, one is slightly stronger for powering the rev-counter.

Incidentally, of the 6 coils in the ventilated alternator stator, 5 are for lighting and the other is for ignition.

SIX SPEEDS

Since the engine has so wide a spread of torque the choice of 6 speeds is more of a concession to fashion than a necessity. Input and output shafts are separate so that all gears are indirect.

The six-plate clutch is dry and the internal ratios are 3.2, 2.0,1.47,1.21,1.047 and 0.95 to 1. Unusually the three selector forks are in aluminium with a special surface treatment.

SPIN-OFF

The Italian industry can be proud of the Moto morini 3 1/2. Inevitably folk will want to convert it for racing - and many both in Italy and the UK continue to do so with great success.

But racing is a spin off. The 72- degree v- twin from Bologna doesn't need track winds to justify itself. As a sophisticated roadster it simply oozes the quality and character it's designer's had the courage to aim for when they first put pencil to paper.