Group 10 - Line Trimmer/Critical Project Review

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Contents

Critical Project Review

Delivery Date: 10/09/2009

Product Reassembly Plan

Introduction:

The purpose of the critical project review is to provide detailed directions and outlines challenges that were encountered in the reassembly of the product that was reverse engineered. The line trimmer was able to be successfully reassembled with only a couple challenges and bumps during the process. Table 3 below outlines all of the steps taken, along with the tools required, time required, a difficulty rating and a picture.


Difficulty Scale:

In order to give an idea of how hard each step is, a scale of difficulty will be established and used throughout the reassembly outline. The scale will range from 1 to 5 with 1 being the most simple a step could be and 5 being the most difficult. A difficulty rating of 1 would be something as simple as refastening a screw that lines up easy and is easy to access. A rating of 5 would involve reassembling something that is very hard to do for most people. An example of this is the starter spring. Rewinding the starter spring takes more time and patience for someone who has not done it before. The spring needs to be gripped tightly while it is wound up and can result in hand cramps. The time taken to perform a step has a relationship to its rating of difficulty. Something that can be done in a minute would have a difficulty rating of 1 or 2 in most cases. Steps that are more time consuming, say 5 to 10 minutes, would have a difficulty rating closer to 4 or 5. Steps requiring a special tool might rate slightly higher on the difficulty scale, but at the same time a step that still only takes a minute with a special tool would not have a rating of 5, it would most likely be around a 2.


Tools Required:

  • Tools needed for reassembly include:
    • 1/4” flathead screwdriver
    • #2 Phillips head screwdriver
    • 5/32” hex key wrench
    • 3/16” hex key wrench
    • 9/16” hex head socket
    • Pliers
    • Needle nose pliers
  • Safety equipment that should be used includes:
    • Safety glasses
    • Protective gloves


Reassembly Steps

Skip Reassembly Steps and continue to Post-Reassembly Topics


Table 3 - Reassembly Steps

Step Description Tools Required Time Required Difficulty Picture
1 Starter Dog

The two starter dogs must be reattached to the flywheel using a screwdriver. Be sure that small torsion spring is positioned properly around the small extrusions on the flywheel.

#2 Phillips screwdriver 1 minute 2
Click to View
2 Flywheel

The flywheel can be slid on over the crankshaft. Be sure to line up the notch on the crankshaft with the key in the flywheel hole. If not the flywheel will not slide down fully into position.

None 1 minute 2
Click to View
3 Drive Coupling Fastening

Place the washer around the crankshaft so that it rests on the flywheel. Begin twisting the drive coupling on by hand until it cannot go any tighter. Next place a 9/16” extended ratcheting socket over the drive coupling to tighten it and with a pair of pliers grip the pin located inside the opening of the crankcase assembly in order to keep the flywheel and crankshaft from spinning with the drive coupling.

9/16” extended hex head socket and pliers 2 minutes 3
Click to View
4 Muffler

The muffler assembly needs to be put back together with the baffles positioned correctly and not upside down. Refer to the picture to the right to verify the correct position.

None 1 minute 2
Click to View
5 Muffler Attachment

Next, the tension springs must reattach the muffler to the combustion cylinder. Attach one spring with the longer hook latching around the combustion cylinder fin and the shorter hook latching into the small muffler case hole. The second spring should then first be attached to the combustion cylinder fin at the longer latch end. Then using a pair of needle nose pliers, get a good grasp on the spring and apply a tension on it so that the smaller latch can be placed into the small hole on the muffler body. CAUTION: The spring may fly if it slips out of the needle nose pliers.

Needle nose pliers 2 minutes 4
Click to View


6 Piston and Connecting Rod

Slide the hole in the connecting rod of the piston assembly back over the pin located inside of the opening of the crankcase assembly.

None 1 minute 1
Click to View
7 Cylinder-Muffler

With the combustion cylinder oriented such that the muffler is farthest from the flywheel, carefully slide the piston into the combustion cylinder (Note: be sure the piston ring is properly lined up and pinched in slightly so it will fit inside the combustion cylinder). Once the combustion cylinder has been slid over the piston, turn the cylinder-muffler assembly a quarter-turn counterclockwise looking at the top of it.

None 2 minutes 2
Click to View


8 Cylinder-Muffler Fastening

Once the cylinder-muffler assembly is sitting on the crankcase assembly appropriately, refasten the two socket head cap screws with a hex drive. These can be tightened via the two holes in opposite corners of the combustion cylinder on the end where the spark plug enters.

3/16” hex key wrench 1 minute 1
Click to View
9 Cylinder Gasket

Replace the cylinder gasket that lies between the cylinder and the carburetor adapter. Be sure that the appropriate holes line up correctly.

None 1 minute 1
Click to View


10 Carburetor Adaptor

Place the carburetor adaptor over the gasket previously replaced making sure that it is oriented such that the screw holes line up. Next fasten the two socket head cap screws with a hex drive that go through the adapter and tighten into the crankcase.

5/32“ hex key wrench 1 minute 1
Click to View
11 Ignition Module

The ignition module attaches to the crankcase on the other side of the muffler-cylinder assembly. Place the ignition module spacer on the crankcase over the holes it lines up with. Next place the ignition module on top of the spacer with the two holes lined up. Feed the two socket head cap screws with a hex drive through the ignition module and spacer. It may be necessary to wiggle around these components to align the screws with the appropriate holes. Once they are lined up, tighten them down with a hex key.

5/32“ hex key wrench 2 minutes 2
Click to View
12 Top Gasket

Replace the gasket that is positioned in between the top cover and the crankcase window exposing the connecting rod of the piston.

None 1 minute 1
Click to View
13 Upper Engine Housing

Carefully place the engine assembled in the previous steps into the upper engine housing. Line up the crankcase window with the extrusion in the engine housing where the gasket was previously placed. Be sure not to damage the carburetor that is attached by the fuel line.

None 1 minute 1
Click to View
14 Upper Engine Housing Fastening

Refasten the four socket head cap screws with a hex drive on the top of the engine cover. These should line up well, if they do not, try starting them one at a time with only a couple turns.

5/32“ hex key wrench 1 minute 1
Click to View


15 Starter Spring Winding

If the starter spring unraveled during disassembly, it needs to be rewound, if not proceed to the next step. To rewind the start spring begin from the inside of the coil and begin wrapping it in as tight of a spiral as possible. Be sure not to let the spring slip while winding it or it will not fit back in the disk. It may be easier to have an additional pair of hands assist in holding the spring tightly while it is being wound. Once it is wound up, carefully place it into the start disk. Make sure only the hook at the end of the spring is hanging out of the disk.

2+ individuals 10 minutes 5
Click to View
16 Starter Spring

Replace the starter spring disk, with the spring coiled inside, into the bottom of the lower engine housing. Line up the hook on the end of the starter spring with the notch on the inside of the casing so that it can grab it when it is spun. Replace the small Phillips #2 head screw in the appropriate hole to hold down the spring.

#2 Phillips screwdriver 1 minute 2
Click to View
17 Pull Start

Replace the pull cord disk over the starter spring in the lower engine housing. Refasten the two socket head cap screws with a hex drive around the perimeter of the pull-cord disk.

5/32“ hex key wrench 1 minute 1
Click to View
18 Lower Engine Housing

Reconnect the ignition module wires to the power switch located on the inside of the cover. The spades may be difficult to slide over the terminals so it is easier to use needle nose pliers. (Note: it does not matter which spade is connected to which terminal.)

Needle nose pliers 2 minutes 2
Click to View
19 Lower Engine Housing Fastening

Place the lower engine housing over the bottom half of the engine such that it lines up with the upper engine housing. Refasten the four socket head cap screws with a hex drive on the bottom of the engine cover. These should line up well, if they do not try starting them with only a couple turns one at a time.

5/32“ hex key wrench 1 minute 1
Click to View
20 Throttle Cable

Slide the throttle cable back through the opening in the lower engine housing. The one end can then be slid back into the carburetor to control the fuel and air flow.

None 1 minute 2
Click to View


21 Air Filter Case

Place the air filter box over the carburetor. This might be a bit tricky because the screws need to go through the air filter box, the carburetor and then into the crankcase assembly. Start by getting one of the two socket head cap screws with a hex drive lined up properly and give it a few turns. Then move around the air filter box and carburetor slightly to line up the other hole. Finally, tighten these screws down.

5/32“ hex key wrench 2 minutes 2
Click to View
22 Air Filter

Replace the steel air filter plate and to the foam air filter in the air filter box.

None 1 minutes 1
Click to View
23 External Air Filter Case

Place the black external air filter case back over the air filter. This can be fastened down via the two Phillips head screws.

#2 Phillips screwdriver 1 minutes 1
Click to View
24 Lower/Upper Engine Housing Attachment

Fasten the socket head cap screw with a hex drive next to the spark plug.

5/32“ hex key wrench 1 minutes 1
Click to View


25 Spark Plug

Screw the spark plug back into the combustion cylinder using a wrench. Push the rubber cap back onto the spark plug.

3/4” wrench 1 minute 1
Click to View
26 Lower Handle

Slide the lower handle over the drive shaft housing and put the provided screw through the clamp and handle so that it extrudes from the handle. Screw the wing-nut on the extruded screw to tighten the handle down in the desired position.

None 2 minutes 1
Click to View
27 Drive Shaft

Place the metal drive shaft in the housing. Slide the drive shaft and housing into the bottom of the engine and engine housing. Be sure to twist and wiggle the drive shaft housing a little bit so that it slides in all the way and the notches line up. (Note: wear protective gloves when handling the drive shaft because there may be small metal shards on it.)

Protective gloves 2 minutes 2
Click to View


28 Drive Shaft Fastening

Fasten the two socket head cap screws with a hex drive recessed into the green casing half an inch above the trigger handle. Use a small screw Phillips screw driver to hold the nuts in place on the other side. Once they are tightened a little the nuts will be held in the notches designed for them in the case.

5/32“ hex key wrench 2 minutes 2
Click to View
29 Trigger Throttle

Slide the throttle cable hammer-head back into the plastic trigger. Then slide plastic trigger back onto its pivot point inside the handle.

None 1 minute 2
Click to View
30 Trigger Handle

Place half of the handle on the underside of the drive shaft housing. Place the other half of the handle on top of the drive shaft housing. They should line up easily and sit nicely around the housing. Pay attention to make sure that the throttle cable is able to exit the end of the handle.

None 1 minute 1
Click to View
31 Trigger Handle Fastening

Screw in the four #2 Phillips head screws on the appropriate side of the plastic handle with the holes.

#2 Phillips screwdriver 1 minute 1
Click to View
32 Foot Guard

Place the foot guard just above the trimming attachment such that it extends in towards the curve of the drive shaft housing. Place the clamp around the drive shaft housing and line up the holes in it with those in the foot guard. Screw the two flat head screws back in.

1/4” flathead screwdriver 2 minutes 2
Click to View

Post-Reassembly Topics

Challenges:

There were several unique challenges during the reassembly that differed from those during the dissection. One particular challenge was rewinding the starter spring back into its disk. The starter spring accidentally unraveled out of the starter spring disk during dissection of the product, therefore the group had to figure out how to wind a 20 foot piece of thin steel into a disk that was about four inches in diameter. It was difficult to hold the spring tightly together after a few windings had been done and it was strenuous on the hands. One of the problems was that the spring had to be wound so small that it was difficult to try and get two pairs of hands on it to help, so it had to be done by one person. Eventually, after a few attempts on several different occasions the group was able to get the starter spring back together. Another more mild challenge was reattaching the muffler to the combustion cylinder via the two tension springs. These springs were very stiff and did not have much space to grab onto. It was difficult to get a firm grasp of the spring with a pair of pliers so that a sufficient tension could be applied to it to place it back in the appropriate hole on the muffler body and combustion cylinder. After a couple attempts this obstacle was overcome without seeking any further assistance. One area that the group noted could also cause trouble was the reassembly of the muffler. The muffler could fit together in a variety of different ways, but they all are not correct. Thus it was a good thing that photographs were taken of the dissection to make sure that the reassembly of the muffler was done correctly. Not reassembling the muffler properly could cause the line trimmer to run louder or emit exhaust gas at a higher temperature posing a danger to the user.


Post Reassembly:

The group was not able to get the line trimmer running before it was dissected. After dissection and reassembly, the line trimmer still does not run. This could be from a variety of problems. The group noted that the pull start mechanism seemed to have a problem in it because the cord would not retract after each pull. After dissection the group was not able to identify what exactly the problem was and upon reassembly it is still the same case. After attempting to start the device several times, the group did note that it smelled as though the fuel mixture was being pumped into the combustion cylinder. The group also tested the spark plug in a different line trimmer and it worked.

The dissection and reassembly processes were nearly mirror images of each other aside from the couple of unique challenges mentioned above. The dissection and reassembly differed in how the starter spring was dealt with and the muffler assembly. These differences are described above. The same set of tools was used for both processes with the exception of one or two items. Reassembly did not require the use of a small hammer and penetrating oil. The entire product was able to be successfully reassembled over the time span of less than an hour.

After completing the analysis of this product a couple recommendations can still be made. Improvements to the start up system would be beneficial because that is where the group thought that the problem lied in the line trimmer. The addition of a primer would be a helpful design revision. This would be a relatively cheap addition and would be able to get fuel into the combustion cylinder for the first pull. Adding an electric start up system could also assist in getting the device running. One way to alleviate some of the weight and cost added with an electric start system would be to use a detachable-rechargeable battery pack. By doing this the user could recharge the batteries inside his or her home between uses. This would eliminate the need for an alternator on the line trimmer.


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