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Video & Articles: Appliance & Equipment RepairBriggs & Stratton Small Engine Piston Assembly Replacement 791786 
Briggs & Stratton Small Engine Piston Assembly Replacement 791786
Total Parts Cost
$NaN32:15
- Description
This video provides step-by-step instructions for replacing the piston assembly on a Briggs & Stratton small engine. The most common reason for replacing this part is if the engine is loud or running rough.
All of the information in this video is applicable to the following brands: Briggs & Stratton
All of the information in this video is applicable to the following brands: Briggs & Stratton
Step By Step Instructions
1
To replace the piston assembly in this briggs and stratton engine, you will need to uninstall the engine from the equipment it’s powering.
2
If the engine is installed on this cub cadet chipper shredder…
3
… you will need these tools to fully uninstall the engine.
4
To replace the piston assembly, you will need these additional tools.
5
Before you begin this procedure, make sure the engine has cooled.
6
We also recommend there be no fuel in the tank or oil in the engine.
7
Use the half-inch wrench to secure the bolts and the half-inch socket to unthread the nuts securing the hopper assembly support plate to the impeller housing.
8
Using the half-inch socket, unthread the six mounting nuts securing the front of the hopper assembly to the housing.
9
With the nuts unthreaded, tilt the hopper assembly back and lift up to fully detach the assembly from the bolts.
10
Remove the shredder plate.
11
Next, unthread the two retaining knob screws securing the bottom of the discharge chute.
12
Use the 7/16th inch wrench to secure the chute’s mounting bolt…
13
… then use the 7/16th inch socket to fully unthread the nut.
14
Slide out the bolt, detach the chute, and remove the two spacers.
15
Use the needle-nose pliers to pull out the retaining pin securing the shredder screen pin and slide the pin out.
16
Next, use the half-inch socket, the small flat-head screwdriver, and the needle-nose pliers to remove the upper mounting screws securing the outer flail housing.
17
With the tow bar installed, tip the chipper shredder back and set a weight on the tow bar to hold it down.
18
Now, using the half-inch socket and the half-inch wrench, remove the ten remaining nuts and bolts securing the outer housing to the inner housing.
19
With all the nuts and bolts uninstalled, fully detach the outer flail housing and set the shredder screen aside.
20
Use the two-by-four piece of wood to prevent the impeller from rotating.
21
Use the 9/16th inch six-point socket with a half-inch driver to unthread the center mounting bolt securing the shredder blade and impeller – this will require some effort.
22
Reposition the wood support to secure the impeller.
23
Now use the 5/8th inch socket to thread the impeller removal tool into the center bolt screw hole.
24
The bottom of the tool will then push against the bottom of the engine shaft to detach the impeller from the shaft.
25
Once detached, unthread the impeller removal tool.
26
Return the chipper shredder to its upright position.
27
Now pull out the retaining pin securing the tow bar clevis pin.
28
Slide out the clevis pin and remove the bar.
29
Tip the chipper shredder back.
30
Use the half-inch wrench and the half-inch socket to remove the nut and bolt securing the left rear corner of the engine base.
31
Use the half-inch socket to unthread the three remaining mounting bolts securing the base.
32
Return the chipper shredder to its upright position.
33
Next, unthread the four mounting bolts securing the engine to the inner flail housing.
34
With the bolts unthreaded, you can now fully remove the engine…
35
… and set it upright on a sturdy surface.
36
Using the 7mm socket, unthread the four mounting screws securing the guard to the muffler.
37
Use the 10mm socket with an extension to unthread the rear screw securing the guard’s mounting strap to the bracket.
38
Remove the guard…
39
… and detach the breather tube from the rocker cover.
40
Now use the 10mm socket to unthread the four mounting screws securing the rocker cover to the cylinder head.
41
You will need to use the 3/8th inch universal joint adapter to unthread the top screw.
42
With the four screws unthreaded, you can detach the cover.
43
If loose, remove the rocker cover gasket.
44
Next, detach the spark plug wire and boot from the spark plug.
45
Use the 5/8th inch spark plug wrench to help loosen the spark plug then unthread it.
46
Confirm the engine piston is in the “up” position, known as the “top dead center”, then lower the piston slightly, making sure both rocker arms stay loose.
47
Use the 5/8th inch wrench to secure the intake rocker arm adjuster nut and the 5/32nd inch allen wrench to loosen the set screw.
48
With the set screw loosened, fully remove the nut and the rocker arm.
49
Slide out the push rod.
50
Now repeat to remove the exhaust valve rocker arm and push rod.
51
Use the 10mm socket to unthread the two screws securing the muffler to the cylinder head.
52
Remove the muffler.
53
Next, use the 5/16th inch nut driver to unthread the two mounting screws securing the air filter cover.
54
Remove the cover and the air filter…
55
…then unthread the screws securing the filter base.
56
Pull the choke lever off so you can fully remove the base.
57
Using the t-30 torx bit, unthread the two mounting screws securing the carburetor, spacer, and gaskets to the cylinder head.
58
Now use the 7mm socket to unthread the screw securing the cylinder head shield.
59
Fully detach the shield.
60
Unthread the four mounting screws securing the cylinder head using the 10mm socket.
61
Set the cylinder head aside.
62
Now tip the engine on its side with the crankshaft facing upward.
63
Use the 10mm socket to unthread the six mounting screws securing the crankcase cover
64
You can use a flat-head screwdriver to help pry off the cover.
65
With the piston in the “up” or the “top dead center” position, lift out the camshaft.
66
If necessary, rotate the crankshaft so you can access the two mounting screws securing the connecting rod cap.
67
Use the 8mm socket to unthread them.
68
Detach the cap.
69
Now rotate the crankshaft so the piston is in the “up” position and you can push the old piston assembly out.
70
Use the awl to detach the clip securing the piston pin.
71
You can use the awl to help dislodge the pin and remove the connecting rod.
72
You’re now ready to prepare the new piston assembly for installation.
73
Insert the connecting rod into the piston with the side showing the “mag” abbreviation facing the arrow on the top of the piston.
74
Insert the pin and secure it with the clip.
75
Next, position the expander ring in the bottom groove of the piston.
76
Align one of the small oil rings below the expander ring and the other above
77
Make sure the gaps in the oil rings and expander ring do not align.
78
Use the expander tool to align the wiper ring in the middle groove, making sure the two stripes are on the right side of the gap.
79
Using the expander tool, align the compression ring, the one with the single yellow stripe, in the top groove.
80
Again, keep the stripe on the right side of the gap.
81
You should also make sure the gaps in the wiper and compression rings are staggered.
82
Now apply some assembly lubrication to the rings.
83
Position the piston ring compressor tool over the end of the piston and use the square wrench to tighten the band to compress the rings.
84
Keep the band loose enough so the tool can slide off when required.
85
Now insert the piston into the cylinder with the arrow pointing to the flywheel and push it into place as the ring compressor tool band slides off.
86
Next, align crankshaft with the connecting rod… then position the cap and thread the two mounting screws.
87
Using the 8mm socket on a torque wrench, torque the screws to 100 inch pounds.
88
Confirm the tappet valves are in place…
89
…and the piston is in the “up” position.
90
Lift off the timing gear washer so you can see the indent mark.
91
Reinsert the end of the camshaft into the bearing in the crankcase and align the gear so the indent mark on the gear aligns with the indent mark on the timing gear when the gear teeth are interlocked.
92
You may have to rotate the crankshaft to align the marks.
93
Replace the timing gear washer.
94
Confirm the crankcase gasket is intact, then realign the cover.
95
Thread the mounting screws in a diagonal order.
96
Using the 10mm socket on a torque wrench, torque the screws to 100 inch pounds.
97
Return the engine to its upright position.
98
Realign the cylinder head gasket on the mounting pins…
99
… then reposition the cylinder head on the crankcase and thread the four mounting screws in a diagonal order.
100
Torque the four screws to 220 inch pounds.
101
Confirm the valve caps on in place on the valve stems.
102
Reposition the cylinder head shield.
103
Thread and tighten the side screw to secure.
104
Realign the carburetor gasket and spacer on the cylinder head.
105
Reinsert the two mounting screws through the carburetor and slide the second gasket onto the screws.
106
Position the carburetor and thread the screws into the cylinder head.
107
Insert the two mounting screws through the air filter base…
108
… then align the base and thread the screws into the carburetor.
109
Replace the choke lever.
110
With the pre- cleaner positioned in the cover followed by the air filter with its rubber gasket facing outward…
111
… align the cover on the base…
112
… and secure it with the screws.
113
Confirm the gasket is intact then reposition the muffler and thread the two mounting screws to secure.
114
We recommend you examine the push rods to see if either one is bent and replace one or both rods with new ones if necessary.
115
Insert both push rods through the guide until they are fully seated in the cylinder head.
116
Realign the intake valve rocker arm and paritally thread the adjuster nut.
117
Repeat to install the exhaust valve rocker arm.
118
Now use the feeler gauge to set the appropriate gap between both rocker arms and their respective valve caps – the intake rocker arm gap should be between .004 and .006 thousandths of an inch…
119
… the exhaust rocker arm gap should be between .009 and .011 thousandths of an inch.
120
Tighten both rocker arm adjuster set screws then recheck the gaps.
121
Rethread the spark plug.
122
Be careful not to damage the threads by overtightening.
123
Reattach the wire and boot to the spark plug.
124
Reinstall the rocker cover by inserting the top mounting screw then slide the gasket, if applicable, over the screw.
125
Align the cover and gasket on the cylinder head and thread the screw.
126
Replace the remaining screws to fully secure the cover.
127
The longer screw goes on the bottom.
128
Insert the breather tube into the hole in the cover.
129
Reinstall the muffler guard by positioning it over the muffler…
130
… then thread the screw to secure the strap to the bracket.
131
Thread the four front mounting screws to secure the guard to the muffler.
132
Reinstall the engine by positioning it on the chipper shredder base with the crankshaft inserted through the hole in the inner flail housing.
133
Confirm the washers are on the screws, then loosely thread the four screws to secure the engine to the flail housing.
134
Tip the chipper shredder back…
135
… then thread and tighten the three mounting bolts to secure the engine base to the base of the chipper shredder.
136
Next, confirm the star washer is aligned on the left rear bolt then insert the bolt… slide on the round washer then thread and tighten the nut to secure the left rear corner of the engine base.
137
Set the equipment upright…
138
… then tighten the four screws securing the engine to the inner flail housing.
139
Keeping the hitch plates tilted downward, reinsert the tow bar into the mounting bracket.
140
Slide in the clevis pin and secure it with the retaining pin.
141
With the tow bar reinstalled, tip the chipper shredder back and support it.
142
Reinstall the impeller assembly by aligning it on the engine shaft.
143
Secure it with the wood support, then rethread the center mounting bolt.
144
Using the 9/16th inch six-point socket on a torque wrench, torque the center bolt to fifty foot pounds.
145
Remove the wood.
146
Position the shredder screen mounting post in the hole in the inner flail housing then realign the outer housing.
147
Thread and tighten the ten nuts and bolts to secure.
148
Rethread the two upper mounting screws using the speed clips.
149
Remove the weight and return the chipper shredder to its upright position.
150
Slide the shredder screen pin through the impeller housing and screen.
151
Insert the retaining pin to secure.
152
Realign the discharge chute on the impeller housing and insert the spacers.
153
Insert the mounting bolt…
154
… then thread and tighten the nut.
155
Fully position the chute then thread and tighten the retaining knob screws.
156
Realign the shredder plate on the six impeller housing bolts.
157
Reinstall the hopper assembly by aligning the support plate on the two upper mounting bolts first then rotate the assembly to align it on the impeller housing bolts.
158
Thread and tighten all eight mounting nuts to secure – we recommend hand-threading the nuts first then using the socket to tighten once all the nuts are in place.
159
Refill the fuel tank, add oil, and the engine should be ready for use.
Description
This video provides step-by-step instructions for replacing the piston assembly on a Briggs & Stratton small engine. The most common reason for replacing this part is if the engine is loud or running rough.
All of the information in this video is applicable to the following brands: Briggs & Stratton
All of the information in this video is applicable to the following brands: Briggs & Stratton
Step-By-Step Instructions
1
To replace the piston assembly in this briggs and stratton engine, you will need to uninstall the engine from the equipment it’s powering.
2
If the engine is installed on this cub cadet chipper shredder…
3
… you will need these tools to fully uninstall the engine.
4
To replace the piston assembly, you will need these additional tools.
5
Before you begin this procedure, make sure the engine has cooled.
6
We also recommend there be no fuel in the tank or oil in the engine.
7
Use the half-inch wrench to secure the bolts and the half-inch socket to unthread the nuts securing the hopper assembly support plate to the impeller housing.
8
Using the half-inch socket, unthread the six mounting nuts securing the front of the hopper assembly to the housing.
9
With the nuts unthreaded, tilt the hopper assembly back and lift up to fully detach the assembly from the bolts.
10
Remove the shredder plate.
11
Next, unthread the two retaining knob screws securing the bottom of the discharge chute.
12
Use the 7/16th inch wrench to secure the chute’s mounting bolt…
13
… then use the 7/16th inch socket to fully unthread the nut.
14
Slide out the bolt, detach the chute, and remove the two spacers.
15
Use the needle-nose pliers to pull out the retaining pin securing the shredder screen pin and slide the pin out.
16
Next, use the half-inch socket, the small flat-head screwdriver, and the needle-nose pliers to remove the upper mounting screws securing the outer flail housing.
17
With the tow bar installed, tip the chipper shredder back and set a weight on the tow bar to hold it down.
18
Now, using the half-inch socket and the half-inch wrench, remove the ten remaining nuts and bolts securing the outer housing to the inner housing.
19
With all the nuts and bolts uninstalled, fully detach the outer flail housing and set the shredder screen aside.
20
Use the two-by-four piece of wood to prevent the impeller from rotating.
21
Use the 9/16th inch six-point socket with a half-inch driver to unthread the center mounting bolt securing the shredder blade and impeller – this will require some effort.
22
Reposition the wood support to secure the impeller.
23
Now use the 5/8th inch socket to thread the impeller removal tool into the center bolt screw hole.
24
The bottom of the tool will then push against the bottom of the engine shaft to detach the impeller from the shaft.
25
Once detached, unthread the impeller removal tool.
26
Return the chipper shredder to its upright position.
27
Now pull out the retaining pin securing the tow bar clevis pin.
28
Slide out the clevis pin and remove the bar.
29
Tip the chipper shredder back.
30
Use the half-inch wrench and the half-inch socket to remove the nut and bolt securing the left rear corner of the engine base.
31
Use the half-inch socket to unthread the three remaining mounting bolts securing the base.
32
Return the chipper shredder to its upright position.
33
Next, unthread the four mounting bolts securing the engine to the inner flail housing.
34
With the bolts unthreaded, you can now fully remove the engine…
35
… and set it upright on a sturdy surface.
36
Using the 7mm socket, unthread the four mounting screws securing the guard to the muffler.
37
Use the 10mm socket with an extension to unthread the rear screw securing the guard’s mounting strap to the bracket.
38
Remove the guard…
39
… and detach the breather tube from the rocker cover.
40
Now use the 10mm socket to unthread the four mounting screws securing the rocker cover to the cylinder head.
41
You will need to use the 3/8th inch universal joint adapter to unthread the top screw.
42
With the four screws unthreaded, you can detach the cover.
43
If loose, remove the rocker cover gasket.
44
Next, detach the spark plug wire and boot from the spark plug.
45
Use the 5/8th inch spark plug wrench to help loosen the spark plug then unthread it.
46
Confirm the engine piston is in the “up” position, known as the “top dead center”, then lower the piston slightly, making sure both rocker arms stay loose.
47
Use the 5/8th inch wrench to secure the intake rocker arm adjuster nut and the 5/32nd inch allen wrench to loosen the set screw.
48
With the set screw loosened, fully remove the nut and the rocker arm.
49
Slide out the push rod.
50
Now repeat to remove the exhaust valve rocker arm and push rod.
51
Use the 10mm socket to unthread the two screws securing the muffler to the cylinder head.
52
Remove the muffler.
53
Next, use the 5/16th inch nut driver to unthread the two mounting screws securing the air filter cover.
54
Remove the cover and the air filter…
55
…then unthread the screws securing the filter base.
56
Pull the choke lever off so you can fully remove the base.
57
Using the t-30 torx bit, unthread the two mounting screws securing the carburetor, spacer, and gaskets to the cylinder head.
58
Now use the 7mm socket to unthread the screw securing the cylinder head shield.
59
Fully detach the shield.
60
Unthread the four mounting screws securing the cylinder head using the 10mm socket.
61
Set the cylinder head aside.
62
Now tip the engine on its side with the crankshaft facing upward.
63
Use the 10mm socket to unthread the six mounting screws securing the crankcase cover
64
You can use a flat-head screwdriver to help pry off the cover.
65
With the piston in the “up” or the “top dead center” position, lift out the camshaft.
66
If necessary, rotate the crankshaft so you can access the two mounting screws securing the connecting rod cap.
67
Use the 8mm socket to unthread them.
68
Detach the cap.
69
Now rotate the crankshaft so the piston is in the “up” position and you can push the old piston assembly out.
70
Use the awl to detach the clip securing the piston pin.
71
You can use the awl to help dislodge the pin and remove the connecting rod.
72
You’re now ready to prepare the new piston assembly for installation.
73
Insert the connecting rod into the piston with the side showing the “mag” abbreviation facing the arrow on the top of the piston.
74
Insert the pin and secure it with the clip.
75
Next, position the expander ring in the bottom groove of the piston.
76
Align one of the small oil rings below the expander ring and the other above
77
Make sure the gaps in the oil rings and expander ring do not align.
78
Use the expander tool to align the wiper ring in the middle groove, making sure the two stripes are on the right side of the gap.
79
Using the expander tool, align the compression ring, the one with the single yellow stripe, in the top groove.
80
Again, keep the stripe on the right side of the gap.
81
You should also make sure the gaps in the wiper and compression rings are staggered.
82
Now apply some assembly lubrication to the rings.
83
Position the piston ring compressor tool over the end of the piston and use the square wrench to tighten the band to compress the rings.
84
Keep the band loose enough so the tool can slide off when required.
85
Now insert the piston into the cylinder with the arrow pointing to the flywheel and push it into place as the ring compressor tool band slides off.
86
Next, align crankshaft with the connecting rod… then position the cap and thread the two mounting screws.
87
Using the 8mm socket on a torque wrench, torque the screws to 100 inch pounds.
88
Confirm the tappet valves are in place…
89
…and the piston is in the “up” position.
90
Lift off the timing gear washer so you can see the indent mark.
91
Reinsert the end of the camshaft into the bearing in the crankcase and align the gear so the indent mark on the gear aligns with the indent mark on the timing gear when the gear teeth are interlocked.
92
You may have to rotate the crankshaft to align the marks.
93
Replace the timing gear washer.
94
Confirm the crankcase gasket is intact, then realign the cover.
95
Thread the mounting screws in a diagonal order.
96
Using the 10mm socket on a torque wrench, torque the screws to 100 inch pounds.
97
Return the engine to its upright position.
98
Realign the cylinder head gasket on the mounting pins…
99
… then reposition the cylinder head on the crankcase and thread the four mounting screws in a diagonal order.
100
Torque the four screws to 220 inch pounds.
101
Confirm the valve caps on in place on the valve stems.
102
Reposition the cylinder head shield.
103
Thread and tighten the side screw to secure.
104
Realign the carburetor gasket and spacer on the cylinder head.
105
Reinsert the two mounting screws through the carburetor and slide the second gasket onto the screws.
106
Position the carburetor and thread the screws into the cylinder head.
107
Insert the two mounting screws through the air filter base…
108
… then align the base and thread the screws into the carburetor.
109
Replace the choke lever.
110
With the pre- cleaner positioned in the cover followed by the air filter with its rubber gasket facing outward…
111
… align the cover on the base…
112
… and secure it with the screws.
113
Confirm the gasket is intact then reposition the muffler and thread the two mounting screws to secure.
114
We recommend you examine the push rods to see if either one is bent and replace one or both rods with new ones if necessary.
115
Insert both push rods through the guide until they are fully seated in the cylinder head.
116
Realign the intake valve rocker arm and paritally thread the adjuster nut.
117
Repeat to install the exhaust valve rocker arm.
118
Now use the feeler gauge to set the appropriate gap between both rocker arms and their respective valve caps – the intake rocker arm gap should be between .004 and .006 thousandths of an inch…
119
… the exhaust rocker arm gap should be between .009 and .011 thousandths of an inch.
120
Tighten both rocker arm adjuster set screws then recheck the gaps.
121
Rethread the spark plug.
122
Be careful not to damage the threads by overtightening.
123
Reattach the wire and boot to the spark plug.
124
Reinstall the rocker cover by inserting the top mounting screw then slide the gasket, if applicable, over the screw.
125
Align the cover and gasket on the cylinder head and thread the screw.
126
Replace the remaining screws to fully secure the cover.
127
The longer screw goes on the bottom.
128
Insert the breather tube into the hole in the cover.
129
Reinstall the muffler guard by positioning it over the muffler…
130
… then thread the screw to secure the strap to the bracket.
131
Thread the four front mounting screws to secure the guard to the muffler.
132
Reinstall the engine by positioning it on the chipper shredder base with the crankshaft inserted through the hole in the inner flail housing.
133
Confirm the washers are on the screws, then loosely thread the four screws to secure the engine to the flail housing.
134
Tip the chipper shredder back…
135
… then thread and tighten the three mounting bolts to secure the engine base to the base of the chipper shredder.
136
Next, confirm the star washer is aligned on the left rear bolt then insert the bolt… slide on the round washer then thread and tighten the nut to secure the left rear corner of the engine base.
137
Set the equipment upright…
138
… then tighten the four screws securing the engine to the inner flail housing.
139
Keeping the hitch plates tilted downward, reinsert the tow bar into the mounting bracket.
140
Slide in the clevis pin and secure it with the retaining pin.
141
With the tow bar reinstalled, tip the chipper shredder back and support it.
142
Reinstall the impeller assembly by aligning it on the engine shaft.
143
Secure it with the wood support, then rethread the center mounting bolt.
144
Using the 9/16th inch six-point socket on a torque wrench, torque the center bolt to fifty foot pounds.
145
Remove the wood.
146
Position the shredder screen mounting post in the hole in the inner flail housing then realign the outer housing.
147
Thread and tighten the ten nuts and bolts to secure.
148
Rethread the two upper mounting screws using the speed clips.
149
Remove the weight and return the chipper shredder to its upright position.
150
Slide the shredder screen pin through the impeller housing and screen.
151
Insert the retaining pin to secure.
152
Realign the discharge chute on the impeller housing and insert the spacers.
153
Insert the mounting bolt…
154
… then thread and tighten the nut.
155
Fully position the chute then thread and tighten the retaining knob screws.
156
Realign the shredder plate on the six impeller housing bolts.
157
Reinstall the hopper assembly by aligning the support plate on the two upper mounting bolts first then rotate the assembly to align it on the impeller housing bolts.
158
Thread and tighten all eight mounting nuts to secure – we recommend hand-threading the nuts first then using the socket to tighten once all the nuts are in place.
159
Refill the fuel tank, add oil, and the engine should be ready for use.
Applicable Product Model
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