Coupling two Aermacchi 250 cylinders; Lino Tonti (financed by the Citroen dealer Umberto Premoli) created the "Linto 500 GP" a race beast, available for private racers, that competed with good results (Gyulay Marzowszky was second next to Giacomo Agostini in 1969 championship) in the World Motorcycle Championship from 1968 to 1970.
The initial design of the engine was for a DOHC with 4 radial valves, but the funds available were not sufficient and, therefore, the solution adopted was to use the cylinders (72 mm bore) and heads with rods and rockers of the Aermacchi Ala d'Oro 250 with a new block. The Linto prototype, still in developement, produced 65 hp at 12.000 rpm.
Thanks to the high power, good torque, and light weight, the Linto was very fast. Keith Turner, for example, won at the Mettet Internationals 1969, where his bike was timed at 160mph on the Mulsane straight (20mph faster than Norton and Matchless), but was very fragile and, when Tonti was hired by Moto Guzzi in 1969, the developement of the bike ended. - Dogwalker
The trellis frame of the Linto was built by the specialist Milanese frame builder Stelio Belletti, with Ceriani suspension and Fontana drum brakes, resulting in a sweet-handling lightweight 142 kg bike . . . . - Mike Hanlon
Along with producing a great deal of power, the engine vibrated so much that it sometimes caused the frame to crack, which is how this bike got it's reputation for being 'fragile'.
5 comments:
Thank you for the back story on how the Linto came to be. That it was planned as DOHC parallel twin and ended up as it did because of cost cutting makes sense to me. Otherwise, why would one choose this lay out over a 90 degree V twin (like Ducati did with their very similar plan of making a 250 single into a 500 race twin. It seems to me after looking at photos of the 250/350 singles that the V twin would have been pretty easy to do. Too bad Harely could not figure that out!
Harley already had a 750cc V-twin engine in the Sportster. https://pergelator.blogspot.com/2016/05/cuba-straits-part-3.html
Harley used to be into racing, but I think that was a long time ago. Might be why Buell split off - he wanted to race Harleys.
https://pergelator.blogspot.com/2014/04/saw-motorcycle-parked-outside-store.html
Yes, the Sportster was a unit construction iron barrel and head 883cc bike. Harley Davidson also had the flat head racers which were 750cc and dominated the 500cc OHV opposition, unless they lost... Harley raced and won at Daytona until the rules were changed in 1969 to allow over head cam and multicylinder engines. Honda won (once), then Triumph several times, then I believe Yamaha and the Tz700 4 cylinder two strokes ended the four stroke reign in racing. This era in the 1960-70's was when the OHV sprint 250 could have easily been made into a 500cc V twin, just like Ducati did at about the same time. It is true that AMF had purchased HD and they were lost in America...
I love Buell's chassis design, his front perimeter brake, the short wheelbase, fuel in frame. I don't like the engine at all and wish he would build a bike for the SV650 engine.
thanks for your website.
"Otherwise, why would one choose this lay out over a 90 degree V twin...?"
As a long-time Aermacchi rider, I can point out that there are, in fact, some very good reasons for Tonti having preferred this configuration over a V-twin.
For one, air-cooling is superior on this to any V-twin; it allows full, symmetrical airflow over both cylinders and heads (on an in-line V-twin, the rear cylinder gets at least somewhat starved of cooling air).
For two more: the center of gravity is kept low for stability, and one doesn't have to worry about clearance between the cylinders and the fuel tank or frame members.
But probably the most compelling reason in this case is because when basing a twin on a single, it is much easier to simply duplicate what already exists in a modular manner in the same plane, rather than trying to reinvent the wheel (so to speak) by adding additional cylinders in additional planes.
Why did most makers of vertical singles -- from BSA and Triumph to Benelli and MV Agusta -- base their twins, triples, fours and even sixes, on simply adding more cylinders in the same plane? Because it is much easier to do, with far fewer complexities around balancing the crankshafts and con-rods, the valve train, carburation, exhaust, etc.
Lino Tonti could've designed any kind of engine he wanted, whether it was a V-twin, or something more exotic. Instead he recognized the virtues of sticking with what Aermacchi horizontal singles already brought to the table, and just expanding upon that.
Clicker, Thank you for your reply. I really like thinking about engines of this era. I appreciate your thoughts, but I wonder if we read the same article. This is a race bike, not a production bike. So if " Lino Tonti could've designed any kind of engine he wanted" why did he build an OHV 2 valve parallel twin? Cost is obviously the answer. In fact it seems you agree. "the most compelling reason in this case is because when basing a twin on a single, it is much easier to simply duplicate what already exists in a modular manner in the same plane, rather than trying to reinvent the wheel (so to speak) by adding additional cylinders in additional planes" If you look at the heads, they are exactly the same, not mirror image. They use the same head twice, so the spark plug is on the left and in the middle. That means the cams for one cylinder are almost certainly inside the block.
Having obsessed over this thought quite a bit, I think it would be rather simple to build an OHV 90 degree V twin, an OHV Ducati in other words. The case would need to be a connecting rod wider, everything from the crank on downstream would need to be stronger to deal with the power and torque. The added cylinder could be vertical. Just like all of the British vertical engines, lots of cooling available. Only on Harleys and other air cooled narrow angle vertical V engines do the rear cylinders lack cooling air. Ducati's do not. The greatest difficulty with the OHV V twin would be casting the heads and barrels to have fins pointed in the direction of the air flow.
He wanted a DOHC engine. An overhead cam drive and DOHC lend themselves to inline engines, somewhat for production cost reasons and a lot because cam drives take up space and their design in the 1960's was still somewhat challenging. While you lump all the "BSA and Triumph to Benelli and MV Agusta -- base their twins, triples, fours and even sixes," together, you left out Ducati. If the parallel twin was such a great design, Ducati would have done it with their 750 GT. They did not. They went with 2 bevel drives, the only thing more bedeviling of mechanics than a single bevel drive. How well balanced is a 90 degree V twin? Very well balanced. Much better balanced than any parallel twin of the era.
What were all of the 360 degree British twins known for? Vibration. Only the Norton Commando tamed the vibrations thanks to Isolastics. Almost all the Japanese four stroke twins were 180 degree cranks, and they have rocking couple, one end of the crank goes up and then the other end goes up. What was the Tinto bike known for? "the engine vibrated so much that it sometimes caused the frame to crack..."
BSA, Triumph, Norton, most every British twin had the same design vertically split cases with only two main bearings. On the 650 Triumph, the mains are 6 inches apart. If the valve train didn't limit the rpms, the crank would. When Norton produced the 750 Combat, the main bearings had to be changed quite a bit to tolerate the crank flex (Superblend). On the Harley Sportster the mains are 3.5 inches apart. That crank flexes a lot less than any of the British twins, except the Matchless which had a center bearing. I am guessing that the Tinto engine has a center main bearing, but that is just a guess.
Well, thank you for reading my diatribe. I hope you enjoyed it and aren't irritated with my exuberance. My most elaborate engine fantasy is the Norton OHV V4, similar to the Ducati but OHV with four cylinders. If only...
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