Nostalgic Hero,Volume 102, April 2004, Interview with Mr. Iida

The following is a professional translation of the article that reports an interview with Mr. Iida, the man that designed Nissan's first OHC, 6cylinder engine, the L20..
In the latter half of 1960's, Nissan Motor Co. (henceforth Nissan) prepared L type engine series, and loaded them on their passenger vehicles. L type engine had a double feature of six series cylinders (6 straight henceforth) and four series cylinder (4 straight henceforth) engines, and, at first they covered the displacement from 1.3 to 2 liters. It is two liters L20 type six straight that was developed first. (Hereafter, the type of the engine model is omitted). It was Hiroshi Iida who was in charge of the engine development that I visited to get the story this time.

Iida was born on November 11, 1936 (Showa 11th) in Kajimachi, Kanda in Tokyo as the youngest child of five children. His parents' home was a dealer in pickles in the shop of old standing of Nakagawa family, and it is said that it is no longer in existence now though the eldest son succeeded. He went to the elementary and the junior high school of a present Ochanomizu Women's University attachment, then to Hibiya high school, and the School of Mechanical Engineering at University of Tokyo, He is a talented man, personification of intelligence.

He acquired the driver's license at age 18 although he was not interested in automobile too much during college days. His favorite subject was vibration engineering, and his graduation research was on shimmy. Shimmy is a phenomenon of direction of the front wheel changing by vibration when the car is running on a high speed, due to an unbalanced rotation of the wheels. The front wheel resonates by the high speed operation. The phenomenon of over convex 100 km/h was generated in an old domestic production car although the shimmy is not generated in automobiles these days.

For his graduation design, Iida selected the engine design. He designed a two cylinder, cold water, flat opposing cylinder engine referring to the engine of the Panhard. At this time, he went to Nissan to get a reference drawing with classmate Hajime Tsuchishinoda (He was also employed by Nissan the same year.) This incident may have triggered his joining Nissan.

Iida graduated from the school of Mechanical Engineering at University of Tokyo in March 1959. He selected Nissan and aimed at Mitsubishi Heavy Industries. First, he sought for an employment from Nissan near his home. The Development force of Nissan at that time was located in Tsurumi, Yokohama, which made his commuting easy from his home in Sendagaya, Tokyo.

He requested for the chassis design. It is because he wanted to make best use of his expertise, the vibration engineering. However, his first practice immediately after his employment in April 1959 was an engine design; this provided him a chance to change his request for assignment department to Design Organization instead. The number of the design team in the Design Organization then was as few as 34 in all. They were producing one liter four cylinder engines that were modified to short stroke of Austin's engine, and the engines for the trucks. Prior to this, Nissan was producing sedans of Austin's in license. At that time, not only Toyota but other automobile manufacturers had contracts of licensed production with oversea manufacturers in order to learn their technology from Europe and U.S.

The designs Iida first took charge of after he was assigned to the Design Organization of the Design Division were the water pump and the lubricating oil pump, and he was also in charge of the complaint measures. As for one-liter engine then was an offset, and sectional abrasion of the metal became a problem. Iida was sent to the Aviation laboratory of the University of Tokyo in order to find the solution. At the university, they conduct basic research that the automobile manufacturers cannot do, and the companies still often send their young engineers there.

After he returned to Nissan from the Aviation laboratory, he became ill with the tuberculosis and was hospitalized for ten months. Fortunately early discovery helped him to recover with only administering treatment. Tuberculosis was the first cause of sickness death then although the inoculation of tuberculosis is no longer compelled now.

On returning from the hospital, he was given a charge of the vaporizer (carburetor), and practiced/studied the vaporizer in Hitachi Ltd. Hitachi supplied vaporizer to Nissan as it has an important role for the improvement of the engine performance,

Iida returned to Nissan again and was assigned to the Second Engine Design Division of the Engine Design Department. The First Division takes charge of the engine of the small displacement installed on the Bluebird and others; and the Second takes charge of the larger displacement engine installed on the Cedric and others, and the large displacement engine for the truck.

In July 1964, Nissan ordered Iida to take charge over the development of a series of two liter six cylinder engines (L20 development sign B601x) for the second generation Cedric. The purpose was for them to vie with Toyota's developing six series cylinder engine for the Crown. Those days, both Cedric and Crown had only 1.9 liter four cylinder engines but the gaining momentum to develop six engines for domestic production was finally at hand.

They developed the L20 engine in only one year.
The first L20 was developed in only one year, and H130 Cedric, the second generation Cedric with this engine was introduced in October 1965. We know how specially expressed development this was because developing a new engine in one year is difficult today even with the full use of CAD. In order to speed the development, they pasted the drawing of L type engine of four cylinders that had already been under development, thus an experimental drawing of the cylinder block quickly was made.

Six straight engines are the forms that add two cylinders per four straight engines, and if two cylinders are extended, an experimental drawing will be completed. Of course, they had to rewrite the size. By the way, if present CAD is used, two cylinders can be added on the screen displays, and the size is calculated automatically.

They developed the valve operating system of L20 referring to six engines of Mercedes Benz (henceforth Benz). In other word, they adopted the OHC style and drove the camshaft in the double row chain by driving 12 valves in a row with the cam through the rocker arm.

An experimental engine was completed in November 1964, four months after they had started the development, and performed the endurance test of the engine bench immediately. It takes 20 days for an endurance test of the Nissan engines as ten day hours in driving for 200 hours in all loads. They did not drive all night because they would not be able to deal with a sudden breakdown if unmanned.

The problem clarified by the endurance test was a wear-out of sliding surfaces of the gear and the rocker arm on the edge in front of the crank shaft, that drove the distributor and the lubricating oil pump. This is because the former gear that they used to drive the shaft that drive the crank shaft directly was a spiral gear that slips greatly, and it caused the latter rocker arm to slip greatly and the chrome plating on sliding surfaces, peeled off.

They solved these wear-out measures by the materials and the surface treatments. Using various materials and various gears and rocker arms that were treated on the surface they repeated the endurance tests and confirmed the materials and surface treatments with high abrasion resistance.

Another problem is that the crack got in the camshaft holder. The camshaft holder had a structure apart from the cylinder head, and the design demanded it to be tightened on by a bolt to the cylinder head. Therefore, when the cam depresses the valve, the camshaft holder is pushed up by the reaction force. The crack was generated by the repetition.

As for the power, they obtained high power of 115ps by adopting SU twin pots that has less inhalation resistance in order to compete the Prince straight six engines that was already in life, however the output adjustment of two carburetors was difficult and the idling rotation was also high, resulting the fuel cost deterioration. Especially, a high idling rotation at stopping created the loud noise, and the complaint adhered from the users after it was on the market.

Larger oil consumption was another problem. An oil fall resulted from the oil going up between the piston and the cylinder, and the intake valve and the valve guide was the cause for it. The oil control ring should be used to prevent the oil raise, but the oil ring in these days, did not stick to upper and lower sides in the seal ditch of the piston, and oil leaked from there.

A present oil control ring is a division type, and the coil spring at the center presses an upper and lower ring against the ring ditch of the piston, and the scratch drop performance of the oil of the ring has been improved.

On the other hand, the oil fall had the problem in the oil seal of the valve stem. Because they used the one with the corner section, which was imperfect. The oil seal with the lip is developed, and this problem is canceled now. The oil fall is generated only on the suction valve side. It is because the inlet port becomes negative pressure by a low load, and oil is sucked.

The engine was improved one year later to solve these problems. Maintenance has improved although they used a single draft carburetor with down draft, and max power turned to 105ps. (Development sign B742X).

The idling rotational speed is lowered, and the stopping engine noise has decreased. The problems persist one after another, after the vehicles had been in the market because of the crash engine development, and the changes become indispensable.

The improvement of L20 continued afterwards. It is because four cylinder series such as L13 and L16 are completed. To share these four cylinder series and the parts, L20 was again designed. L type series of four cylinders was developed over time, and had been rationalized to detailed parts. It was too good to miss these parts. Reduction in costs can be attempted by sharing parts. The engine that shared parts was called a module engine.

The redesigned L20 is L20 (A), installed long afterwards for FR vehicles of Nissan. L20 (A) was expanded the bore pitch more than L20, and had enough room and space for the displacement improvement in the future. In fact, L20 (A) has developed into L24, L26, and L28 repeating the bore and stroke improvements. L24 was Fair Lady 240Z, and exported to the United States. A domestic race was taken an active part moreover, and I personally witnessed Datsun 240Z driven by Kunimitsu Takahashi and Motoharu Kurosawa team won the championship on July 26, 1970 in all-Japan Fuji 1000km race.

L type series was low-cost and long life engine. L type series including four cylinders have become long life engines. It was because it is a low-cost engine and was excellent in its basic design. It was a too strong and heavy engine according to today's standard, but it meant that there was enough room that allowed the output improvement for the race. Many domestic engine tuners marked it, and undertook L type engines.

L type series had nine kinds of displacements; combining three kind of bores and four strokes, with four cylinder engines and six cylinder engines, and they shared parts among multi step displacements. In fact, L24 and L26 are the same bore, and it is the same as L13 and L16 of four cylinders. In addition, if the same bore and stroke as L20 (B) that was four cylinder engine of the maximum displacement of installing were adopted for Datsun truck for export; logically speaking, as many as six straight engines were also possible for three liters.

A strong engine was also the best for supercharging. The domestic manufacturers began the power competition again in the early 80's when the exhaust gas measures had completed the first stage. At this time, Nissan chose the exhaust turbo supercharging. The turbo-charger was added to L20 (A). Because the turn flow of L type series was most suitable for the exhaust turbo supercharging.

Moreover, the journal diameter of the crank shaft having a thickness of 55mm allowed the load of supercharging. The turn flow is suitable for the exhaust turbo supercharging because of the mechanism into which the turbo-charger uses the exhaust energy, the turbine is driven, and suction is compressed with the compressor. The inlet port and the exhaust port on one side of the engine become the supercharging engines only by the exhaust breathing in - installing the turbo-charger close to that, and connecting them in a certain turn flow.

However, when the intercooler was installed, the turn flow did not necessarily become an advantage. The intercooler was recent turbo charged engines, and with the improved performance, turbo DOHC engine of crossing flow was supercharged. The purpose of the attempt was to obtain a high performance by a synergy effect of the combination of an efficient DOHC engine and the exhaust turbo super charging.

The following L type engine series were leading engines of Nissan for 20 years. We may say that the long lasting engine is a good one, but on the other hand, the advancement of the engine technology can slow down. If they kept on making the same engine, adopting a new technology would be difficult.

Therefore, Nissan developed the RB20 series in about 80's. OHC of RB20E and DOHC of RB20DE were prepared among the RB20 series, and they both became close flow. However, the bore and the stroke are the same 78.0x69.7mm as initial L20.

Iida stepped back from the charge of six L type cylinder engine in January 1968, after L20 (A) had been developed. It is because the company transferred the charge of six cylinder engine from the Second Engine Designing Division to the First Engine Designing Division. The Second Engine Designing Division took charge of A10 engine instead, which had already been Sunny.