In Part One of our story on manufacturing Mitsubishi V6s we looked at casting iron and aluminium engine components. In Part Two we move on to machining, assembly and testing...
Machining Plant
Once cast, the iron components (the block, camshafts and exhaust manifolds) and the aluminium components (the heads and intake manifold) are delivered to the machining plant. Here, the components are faced, drilled and bored as required.
The aim is to prepare items for the main engine assembly line.
Iron Machining...
The engine blocks are prepared through a series of drilling and facing machines. Each machine has a specific task to perform - one machine is used just to form the rear oil seal recess, for example. In addition, the top and bottom sealing faces are milled flat and the cylinder bores are machined to 93.0mm for the 3.5-litre engine, while the 3.0-litre version is taken out to only 91.1mm diameter.
Each block takes around 10½ hours to be fully machined.
Another line is dedicated to machining the newly cast iron camshafts. As seen in this photo, the camshafts arrive from the foundry in a basic, raw state.
Each camshaft is manually handled through a series of machines that progressively remove surface material toward the specified cam profile. The profile is different across the 3.0-litre, 3.5-litre and Ralliart range.
Before the desired cam profile is achieved, however, each camshaft is induction hardened (using an electric field) to a penetration depth of 2.5mm. Once hardened and fully machined, the camshaft is subjected to a non-destructive magnaflux test to identify any cracks or stress zones.
After a final inspection and gauging, the camshafts are then washed in a water/corrosion inhibitor mix. They are now ready for transportation to the main engine assembly line.
Aluminium Machining...
Once arrived from the post-casting fettling area, the cylinder heads pass along an extensive machining line.
The cylinder head machining line has a number of automated machines. These machines are dedicated to milling the top and bottom surfaces, drilling, tapping and valve guide reaming. No machining is concentrated inside the ports or the combustion chamber, however the Ralliart Magna does require de-shrouding of material around the inlet and exhaust valves.
The intake manifolds that arrive from the aluminium fettling area require machining of the mounting faces, as well as drilling, reaming and tapping the injector and attachment holes.
Note that - other than the in-house cast block, camshafts, heads, intake and exhaust manifolds - Mitsubishi sources a large percentage of the V6 engine components from outside suppliers. Some of these components - such as oil pumps and oil pans - require final machining by Mitsubishi, but most arrive ready for the production line.
Assembly Line
There are two areas to the assembly line - the cylinder head assembly line and the main engine assembly line.
In the cylinder head assembly line, a team of around eight workers installs the camshafts, valves, valve springs and all of the valvetrain hardware into the heads. We're told manual labour is required for this task because of the many complex steps involved.
Once the cylinder heads are assembled, they join the main engine assembly line.
We're told the main engine assembly line "relies on conscientious employees operating in a highly efficient environment". In other words, it's a high stress environment. Each engine is secured on a cradle and is carried along by a conveyer; the conveyor operates at a constant speed and seldom stops. A workstation dedicated to one specific task is set up about every two metres along the line. Approximately sixty-two people work on the main engine assembly line.
The first phase in the main engine assembly line focuses on the bottom-end - the block is equipped with the crankshaft, conrods and pistons. Following this, the engine is rolled over using a metal stand and the pre-assembled heads are installed. Next come the intake manifold, plenum rocker covers, pulleys, sensors and the ancillary systems. Sump oil is also added.
Once the engine is assembled and all its hardware fitted, it undergoes a vacuum leak test to ensure there aren't any ring or gasket leaks. Every engine then undergoes a so-called "hot test" cycle.
The hot test sees the engine quick-fitted to an engine cell, which is rigged to deliver fuel and engine control. Once hooked up, the engine is run at 2500-3000 rpm for around 6 minutes, enabling inspection for oil leaks, oil pressure, misfires or rough running.
In addition to this, typically one engine per day is plucked from the assembly line and subjected to a 'proper' eddy-current dyno test. The unlucky engine is run through an rpm and load cycle for 3 hours to check its output, compression, oil pressure and oil consumption. It then receives a tear down to measure bolt torque, bearing and bore wear.
The remainder of engines from the main assembly line are stockpiled and - when required - loaded onto a truck destined for the Tonsley Park vehicle assembly plant. Each engine is given a specific identification tag, which matches the particular vehicle being built. At present, around two hundred and thirty engines are being built daily - though this varies upon demand.
Based on AutoSpeed's recent positive experiences with the Mitsubishi V6, we can see good reason why demand will increase...
Contact:
Mitsubishi Motors Australia
www.mitsubishi-motors.com.au
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