Group 10 - GM V-6 Engine Gate4
Gate 4: Critical Design Review
This gate provides step by step instructions for the reassembly of the engine along with a scale of the difficulty for each step. It also includes three design revisions at the system level on ways to improve the efficiency and performance of the engine.
Project Management: Critical Project ReviewCause for Corrective Action
During the reassembly of the engine, problems involving group 11 were successfully resolved. Previously, there was miscommunication between the two groups about when the engine would be disassembled, reassembled or when parts would be returned. As soon as work began on this gate, leaders from both groups met and discussed when the engine would be reassembled. We typically went to the lab at night and Group 11 typically worked in the morning. By resolving our conflicts early, both groups were able to separately reassemble the engine and gather the necessary information and pictures without coming in the way of each other.
Project Archeology: Product ExplanationProduct Reassembly
The following steps will guide you through the assembly process and the images with descriptions below are to be used as a reference to which part is being referred to.
The assembly process is essentially the exact opposite of disassembly. The main difference between reassembly and disassembly is that the orientation of certain parts needs to be taken into account for reassembly. The pistons and there respective connecting devices need to be properly aligned to the front of the engine and in there own specific cylinder to prevent excessive wear.
- Install oil pump, fasten to the bottom of the engine block with 1 5/8" hex head bolt. There is a hole on the pump which must align with the matching hole on the block. A rubber hose is used to connect the two pieces.
- Set the crankshaft into block so the sprocket is facing the front of the engine (Away from the engine stand). There are three main bearing caps that hold the shaft in place. Each is fastened with (2) 5/8" hex head bolts. The arrows on the caps should point to the front of the engine.
- Now you can spin the engine 180° to install pistons. Use a ring compressor so the piston will slide into the cylinder. There is an indicator mark on the piston which also points toward the front. All six pistons can be installed at once and then attached to the crankshaft with the connecting rod bearing cap, each has a pair of aluminum bushings that also need to be installed.
- Install the camshaft, the end with the helical gear is inserted first. It will require some force to fully seat the shaft. Hit the end with a rubber mallet. The retaining collar is bolted to the block with 2 T-30 counter-sunk bolts.
- Install lifter into the lifter covers and slide them into the holes on between the cylinder banks. There will be six per side, the cover bolts onto the block with 2 10mm bolts that a permanently held in the covers.
- Install the distributor shaft, It bolts into place similarly to the camshaft.
- Install the distributor into the engine block. There is a hole on the top rear of the engine that the distributor fits into. It is fastened with one 1/2" hex bolt. If it is properly installed into shouldn't twist if you try and spin it.
- Install the helical gear on the end of the camshaft. It should mesh with the helical gear on the distributor shaft. It is not fastened yet, it is bolted on with the timing sprocket.
- Install timing sprocket on camshaft with timing chain around it and the sprocket on the crankshaft. Both the helical gear and this sprocket should line up with the alignment stud on the camshaft. Three 1/2" hex heads bolt the sprocket and gear to the camshaft.
- Install the harmonic balancer onto the crankshaft. It slides onto the keyed shaft.
- Bolt on the timing chain cover, there is a gasket on the bottom so it has to go in at an angle. It bolts on with six 3/8" hex bolts that have rubber bushing. The gasket may make it difficult to get the bolts started, a power drill with a socket end can be used.
- Press the harmonic balancer on the keyed shaft of the crankshaft. A special press is needed to properly install this part. It will take some time and a considerable amount of force to install. Keep pressing it on until it stops moving.
- The serpentine pulley is bolted onto the harmonic balancer with 3 1/2" hex bolts.
- Install the water pump on the front of the engine. There are 4 14mm hex bolts. The tubes should be facing up on the pump. There are 2 rubber hoses that fasten from the pump to the engine block.
- Install the cylinder heads to the top of the engine block over the pistons. They fasten to the block with 12 14mm hex bolts per head. To make sure the heads are installed correctly, check to make sure the 12 holes for the push rods should be toward the center of the engine.
- Drop in push push rods. There are 12 per head, in order to make them fit some of the rockers may need to be loosened and turned.
- Install the valve cover on each head, one cover has a plastic tube on top which goes on the left cylinder bank(when looking at the front).
- Install intake manifold between the cylinders fastening with 8 1/2" hex bolts. The bolt holes will only line up when it is properly oriented. The large black metal tube should be towards the front of the engine.
- Install the fuel injector cover on top of the intake manifold. 8 10mm studs fasten the cover in place, there are 2 longer studs that go in the back left corner. The shorter studs will not thread in these holes.
- Install throttle body on the top of the injector cover. 3 10mm hex bolts fasten it to the cover.
Quickly and easily installed by hand. Very little force and maneuvering was required to put the part in place.
Quickly and easily installed but tools were needed. Still very little force and maneuvering was required to put the part in place.
Easily installed, tools were needed but time consuming and/or repetitive. Little force was used but may require some maneuvering.
Required moderate force, skill, or special tools. Part was heavy and was not easy to put in place.
Required excessive force and time. Tools were needed and precision was necessary.
The Assembly Process
|Step||Part Installed||Difficulty||Tools Used||Quantity / Size of Bolts Installed||Notes||Photos|
|1||Oil Pump||1||Socket Wrench|| 1 x 5/8 in. Hex Head
2 1/8 in. Long1 1/8 in. Thread
|Easily added, somewhat tight area that not all wrenches fit into|
|3||Crankshaft||1||Socket Wrench|| 2 x 5/8 in. Hex Heads
3 1/4 in. Long1 in. Thread
|Crankshaft can be inserted by hand, then bearing caps are fastened with bolts. Crankshaft itself easily installed, attaching other components is time consuming|
|4||Pistons (6)||1||Socket Wrench, Ring Compressor||2 x 14mm Hex Nuts (12)||First, insert pistons. Piston rings had to be compressed before they could be installed into cylinders. Installation was very repetitive but relatively simple. Each piston had an indicator mark that pointed to the front of the engine. Cylinders were numbered odd on the left bank and even on the right relative to the flywheel. Second, connect bearing sleeves to crankshaft and fasten them with bolts. Both main bearing cups and pistons have directional markings that point towards the front of the engine|
|2||Oil Pan||2||Socket Wrench|| 10 x 1/2 in. Hex Heads
3/4 in. Long 2 x 1/2 in. Hex Heads 3 1/8 in. Long7/8 in. Thread
|The oil pan needs to slip over the oil pump and it will set flush on the bottom of the engine block.|
|5||Camshaft||2||Socket Wrench||2 x T-30 Countersink Bolts 3/8 in. Long||Camshaft was easily slid into place and fastened with plate.|
|6||Distributor Shaft||2||none||none||Plastic, removed by hand|
|7||Camshaft Sprocket||2||Socket Wrench||3 1/2 in. Hex Heads 1 3/8 in. Long||Sprocket is aligned with alignment hole and fasten to shaft. Timing chain is also installed at this time. Put chain around both sprockets (Camshaft, Crankshaft) then fasten.|
|8||Water Pump||2||Socket Wrench||4 x 14 mm Hex Heads 2 in. Long||Bolts on front of engine block. Make sure the hoses are on the top.|
|9||Balancing Shaft||2||Socket Wrench|| 2 x T-30 Torx Bolts
1/2 in. Long 1 x 3/8 in. Hex Head with 3.18 in. Washer1 1/8 in. Long Hex Head
|Slides into blind bushings between cylinder banks. Tap with hammer until fully seated.|
|10||Plastic Lifter Covers||1||Socket Wrench||2 (Per Cover) x 10 mm Hex Heads (Permanently Pressed into Cover)||Rotated engine so lifters were horizontal to install, install lifters in covers then slide into holes.|
|11||Lifters||1||none||none||placed by hand into lifter covers first, then into engine|
|13||Cylinder Heads||2||Socket Wrench||12 x 14 mm Hex Heads||Installation required loosening some of the rockers. They interfered with the wrench reaching the bolts.|
|12||Push Rods||1||none||none||Dropped into place through holes in head. Each should line up with a rocker.|
|14||Exhaust Headers(2)||1||Socket Wrench||12 (6 Each) x 14mm Hex Heads 2 in. Long||Two missing bolts. Iron construction and outer location subject material to rust. Has steel heat shield. Gaskets made of multiple layer steel provide air tight seal to contain exhaust gasses.|
|15||Valve Covers (2)||2||Socket Wrench||6 (3 Per Cover) x 1/2 in. Hex Heads 3 1/2 in. Long||Branded with Vortec name, bolted on to heads|
|16||Intake Manifold||2||Socket Wrench||8 (4 Each) x 1/2 in. Hex Heads 1 3/4 in. Long||Installed between cylinder banks. Only fits on way, bolts into place.|
|17||Fuel Injector Cover||1||Socket Wrench||6 x 12 mm Hex Heads||Make sure all wires are under cover, otherwise it will not properly seat, bolts onto intake manifold.|
|18||Spark Plug Coil Pack||1||Socket Wrench||2 x 10 mm Hex Heads||Bolts onto intake housing. There are 2 bolt holes for it on the left side of engine with the flywheel facing away.|
|19||Throttle Body||2||Socket Wrench||3 x10 mm Hex Heads||Bolts to fuel injector cover.|
|20||Harmonic Balancer||5||Pully puller/press, Wrenches||none||Very tight press fit, needed special pulley remover to take off and pulley press to put back on|
The methods and tools used during our assembly were very different from the methods and tools used by GM during manufacturing. While the order in which the parts were put together is essentially the same, the way it was done is very different in factories. Hundreds of engines need to be assembled daily, so the factory uses almost entirely automated assembly lines to maximize efficiency of the assembly. They also use specially designed air tools to affix fasteners quickly and efficiently. Automated assembly allows every product produced to be almost identical, and it allows a high precision with required specifications such as torque. During the product dissection there was limited experience and resources available to complete the dissection, the whole process was a valuable learning experience for the entire group. There were no power tools or torque wrenches used, and also no lubricant used for reassembly for safety reasons in the lab.
Variable Valve Timing:
- This engine currently uses a fixed camshaft and therefore fixed valve timing. Variable valve timing allows the engine to adjust the valve timing depending on the engine speed. To fully understand why this is important one must first realize that the valves do not open and close at Top Dead Center (TDC) and Bottom Dead Center (BDC). It is best to break the process into its individual steps. During the intake stroke, air is sucked into the cylinder because of a partial vacuum created by the pistons movement. The incoming air has a mass and velocity so therefore it has momentum. This momentum causes the air to continue rushing into the cylinder even after BDC. The valve is held open for a certain time to allow this air to enter. If the valve is open too long reversion occurs which is when the air begins to escape through the intake valve. The valve timing should be adjusted so the valves closes right when this reversion begins to occur. For high RPM the valve is open longer and shorter for lower RPM. This allows the maximum amount of air to enter the cylinder for each engine speed. After the intake stroke the compression stroke begins. During this process both valves remain closed so the air/fuel mixture can be compressed for ignition. Once the piston reaches TDC the spark fires and ignites the fuel/air mixture sending the piston back down in the power stroke. Just before the piston reaches BDC on the power stroke the exhaust valve opens. This allows some of the exhaust gas to begin to release before the piston starts the exhaust stroke. This decreases the back pressure on the piston, which can rob horsepower from the engine. Properly adjusting this timing will minimize the internal power losses of the engine. Next, during the exhaust stroke, the exhaust valve is held open for a few degrees past TDC for the same reason as before. The exhausting air has momentum and continues to leave the cylinder. The goal is to get as much air out as possible so fresh air can fill the cylinder and variable valve timing can maximize this. Lastly, there is a period of overlap when both valves are open. Just before the piston reaches TDC on the exhaust stroke the intake valve opens. Air doesn't escape through the intake however, because the exhaust manifold creates a low pressure wave that pulls the air out of the cylinder faster than normal without letting it escape through the intake valve. Variable valve timing can adjust this overlap time to match the engine speed as well.
According to fueleconomy.gov, the average fuel savings is 5% and a total savings of $1,300. There is also the benefit of decreasing harmful pollutants produced by the engine. The appeal to a consumer base is that they will be able to obtain more efficient and environmentally friendly power from the same engine. Currently, there are several ways to implement VVT in engines, involving mechanical and hydraulic methods. The cost difference between an engine with VVT and one without considering the lifetime of the engine is nominal.
Edgar, Julien. "AutoSpeed - Variable Valve Timing." AutoSpeed - Technology, Efficiency, Performance. Web. 09 Dec. 2010. <http://autospeed.com/cms/title_Variable-Valve-Timing/A_110859/article.html>.
"Engine Technologies." Fuel Economy. Web. 09 Dec. 2010. <http://www.fueleconomy.gov/feg/tech_engine_more.shtml>.
"Toyota VVT-i." Toyota Australia: New Car: Details: Prices: Brochure: Dealer: Test Drive: Toyota New Car Australia. Web. 09 Dec. 2010. <http://www.toyota.com.au/toyota/main/vvti/index.htm>.
"Variable Valve Timing." Autotropolis. Web. 9 Dec. 2010. <http://www.autotropolis.com/wiki/index.php?title=Variable-valve_timing>.
Increase Compression Ratio:
- High compression pistons would be an possible design revision for the Vortec V6. They maximize the compression ratio within the cylinder which increases the thermal efficiency of the motor. High compression pistons have a dent forming out the top of the piston similar to a dome shape which decreases the volume of the area above the piston. By decreasing the volume, the pressure within the piston is increased. If the pressure gets too great, the fuel can auto ignite. The auto ignition throws off the timing of the system because the fuel ignites before the power stroke is supposed to occur. This occurrence is why there is a maximum compression ratio. Along with the pressure increasing from the high compression pistons, comes the necessity for reinforcement of the engine block. The new pressure could be higher than the engine block was originally designed to withstand. The block can be physically designed different to handle the higher compression ratio, or it can be made of a different, stronger material, such as aluminum. Other changes to the engine would include changes to emissions control systems, then engine computer (ECU). The price of all the components and the chance of ruining the engine make this option very risky and an option viable for only consumers who are proficient at tuning an engine. After the tuning to increase compression ratio is completed, a higher octane fuel would have to be used at all times to prevent detonation (auto-ignition of the fuel before the spark plugs can ignite it). The process would increase harmful emissions to the atmosphere and reduce the fuel efficiency. If a consumer would be willing to take the risk and disadvantages of harming the environment and paying more to run the engine, they would enjoy more power output of the engine. The reason engines are not tuned accordingly from the manufacturer is that the process can reduce the reliability of the engine. Therefore this option would never be reasonable revision for an engine manufacturer, but a possible revision for a tinkering consumer.
- The engine now has one camshaft located between the cylinder banks, which requires a series of lifters, lifter covers, and push rods to move the rockers which open and close the valves. Changing to an overhead cam system would eliminate these parts. This would move the camshaft from its location to the top of the cylinder head. The overhead camshaft would now directly push the rockers instead of going through the lifters and push rods. This would decreases the amount of moving parts and also decrease friction and power loss generated within the engine due to less reciprocating mass of the camshaft. This revision would require some other major changes in the engine. The timing system would need to be changed to connect both new camshafts. The rockers would also have to be redesigned to work with the cams instead of the push rods, but could also be eliminated with the right design. This would also decrease wear on the engine by decreasing the load on each camshaft and eliminating points of mechanical contact. From a manufacturers perspective, they could market a more advanced reliable product that uses similar if not fewer resources and manufacturing processes with a higher torque output at a comparable price per engine. The cost for redesigning the engine would be significant. That cost could be offset if the manufacturer raised the price of the engine as a more advanced product compared to competitors. The simpler engine design would also appeal to consumers as an engine that would have lower service costs in its lifetime.
- Video of Pushrod Engine
- This is the current setup of the GM V-6. A single camshaft controls the valve timing for the entire engine utilizing pushrods to extend the reach of the camshaft lobes.
- Video of SOHC Engine
- This is an animation of an engine cylinder with a Single Overhead Cam, controlling the intake and exhaust timing for the values of a single side of cylinders. Note there are no pushrods.
Use Overhead Cams:
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