visual inspection of the piston

Reuse And Salvage Guidelines Visual Inspection of the Piston{1214}

Visual Inspection of the Piston{1214} SMCS - 1214

Engine:Commercial All 3044C (S/N: 3441-UP)

Engine:Truck All Industrial Engine:with Turbochargers All Machine Engines: All Marine Engine:with Turbochargers All

Introduction This Reuse and Salvage Guideline contains the necessary information in order to allow a dealer to establish a parts reusability program. Reuse and salvage information enables Caterpillar Dealers and customers to benefit from cost reductions. Every effort has been made in order to provide the most current information that is known to Caterpillar. Continuing improvement and advancement of product design might have caused changes to your product which are not included in this publication. This Reuse and Salvage Guideline must be used with the latest technical information that is available from Caterpillar.

For additional information about this guideline, consult Repair Process Engineering of the Marketing and Product Support Division at 1 (309) 675-5434.

Summary The engine reconditioning does not necessarily result in the installation of new pistons as part of the process of reconditioning. Pistons that meet the specifications in this guideline and other applicable guidelines can be expected to have the same performance in the same application until the next overhaul.

Compare the pistons from this guideline with the pistons that are removed from the engine. This guideline gives specific types of wear. Some pistons cannot be salvaged.

Reference this guideline before reusing a piston. The pistons that are considered unacceptable in this guideline should not be reused.

Piston failure can be due to poor engine performance. Always correct the true cause of the original failure.

Note: Salvaging pistons with extensive damage may not be practical due to labor costs.

References Reference Refer to Reuse and Salvage Guidelines, SEBF8059-12, "Procedure and Specifications to Clean and Measure Pistons".

Reference Refer to Reuse and Salvage Guidelines, SEBF8051-05, "Inspection and Measuring Procedures for Piston Pins".

Reference Refer to Contamination Control Guidelines, PEBJ0002, "Caterpillar Dealer Contamination Control Compliance Guide".

Reference Refer to Special Instructions, SEHS8696, "Piston Cleaning Procedure".

Tooling and Equipment

Refer to the latest version of the Service Manual, NENG2500, "Tools and Shop Products Guide" for any changes.

Nomenclature

Shutdown SIS

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Product: GEN SET ENGINE Model: 3408 GEN SET ENGINE 78Z Configuration: 3408 GENERATOR SET ENGINE 78Z00001-01143

Media Number -SEBF8049-16 Publication Date -09/06/2006 Date Updated -12/06/2006

i02563276

Table 1

Tooling and Equipment

Part Number Description

6V-7894 Microlite

6V-2196 Microscope

of 533408 GENERATOR SET ENGINE 78Z00001-01143(SEBP1379 - 01)/Basic Search

5/22/2008https://sis.cat.com/sisweb/sisweb/techdoc/techdoc_print_page.jsp?returnurl=/sisweb/sisweb/fulltext/fulltextheaderinfoframeset.jsp&called...

Illustration 1 g01198372The piston is from a 3114 engine or the piston is from a 3116 engine.

(1) Crown

(2) Crater

(3) Ring Band

(4) Ring Grooves

(5) Ring Lands

(6) Skirt

(7) Pin Bore

(8) Snap Ring Groove

(9) Top Land

(10) Cooling Jet Relief

(11) Skirt Relief

Illustration 2 g01198447

The piston is from a 3114 engine or the piston is from a 3116 engine.

(1) Crown



(2) Crater

(3) Ring Band

(4) Ring Grooves

(5) Ring Lands

(6) Skirt

(7) Pin Bore


(9) Land

(10) Skirt Relief

Illustration 3 g01198161The piston is from a 3400 series engine of the direct injection type with a double ring land.

(1) Crown

(2) Crater

(3) Ring Band

(4) Ring Grooves

(5) Ring Lands

(6) Skirt

(7) Pin Bore


(9) Top Land


(11) Skirt Relief



Illustration 4 g01198198The piston is from a 3400 series engine of the direct injection type with a single ring land.

(1) Crown

(2) Crater

(3) Ring Band

(4) Ring Grooves

(5) Ring Lands

(6) Skirt

(7) Pin Bore


(9) Top Land


(11) Skirt Relief


The piston is from a 3500 series engine.

(1) Crown

(2) Crater

(3) Ring Band

(4) Ring Grooves

(5) Ring Lands



(6) Skirt

(7) Pin Bore


(9) Top Land


(11) Skirt Relief

Illustration 6 g01198322The piston from a typical precombustion chamber engine

(1) Crown

(2) Valve Pocket

(3) Heat Plug

(4) Crater

(5) Ring Band

(6) Top Ring Groove

(7) Middle Ring Groove

(8) Oil Ring Groove

(9) Third Ring Land

(10) Skirt

(11) Pin Bore


(13) Top Ring Land

(14) Second Ring Land


(16) Skirt Relief



Note: The piston and piston pin must be identified and marked with the cylinder number and orientation in reference to the front of the engine.

Note: Do not mix and match pistons and piston pins from different cylinders. Ensure that the pistons and piston pins are oriented properly to the front of the engine upon reassembly.

Illustration 7 g01198332One-piece piston with a coating of graphite

NOTICEIf the pistons and piston pins have been worn together, mixing the parts can possibly lead to pin rotation issues.

Illustration 8 g01198333Nomenclature for ring grooves

(1) Ring Band

(2) Top Ring Land


(4) "J" Groove

(5) Skirt



General Procedures Follow the instructions in this guideline in order to determine if a piston is reusable.

1. Make a visual check of the overall condition of the piston.

2. Clean the piston thoroughly.

3. Reinspect the piston after cleaning for the following.

Cracks

Scuffing

Holes

Additional visible damage

4. The following areas of the piston should be inspected before reusing.

(a) Ring Band

(b) Ring Groove

(c) Ring Land

(d) Skirt

(e) Pin Bore

(f) Snap Ring Groove

5. Measure the piston according to the specifications in the Reuse and Salvage Guidelines, SEBF8059, "Procedure and Specifications to Clean and Measure Pistons".

Initial Inspection Make a quick visual inspection of the piston before cleaning. If no obvious faults are found, clean the piston according to the instructions in the Reuse and Salvage Guidelines, SEBF8059, "Procedures to Clean and Inspect Pistons".

Visual Inspections

Top of Piston

Illustration 9 g01198336Nomenclature for ring grooves

(1) Third Ring Land

(2) Ring Band

(3) Top Ring Land


(5) "C" Groove

(6) Skirt



Small cracks around the heat plug are normal. To measure these cracks, use a 34 gauge wire that has a diameter of 0.15 mm (0.006 inch) as a gauge. A 6V-2196 Microscope and 6V-7894 Microlite can also be used.

Use the piston again.

Do not use the piston again.

Illustration 10 g01198512Small cracks that are less than 0.15 mm (0.006 inch) wide around the heat plug.

Illustration 11 g01198517The arrows show cracks that are wider than 0.15 mm (0.006 inch).

Illustration 12 g01198526If necessary, use a 6V-2196 Microscope and 6V-7894 Microlite to measure the size of the cracks around the heat plug.






Illustration 13 g01198531View the cracks through the eyepiece of the 6V-2196 Microscope . This crack is wider than 0.15 mm (0.006 inch).

Illustration 14 g01198535Large cracks connected to each other.

Illustration 15 g01198540Crack (A) goes into the valve pocket. Cracks (A) and (B) are wider than 0.15 mm (0.006 inch).






Do not reuse the piston if the piston shows signs of contact with a valve or contact with valves. See Illustrations 19, 20, 21 and 22.

Illustration 16 g01198569The crack goes across the area between the valve pockets.

Illustration 17 g01198570Cracks in the crater that are not wider than 0.15 mm (0.006 inch)

Illustration 18 g01198573Crack (A) goes into the valve pocket. Callout (B) shows cracks that are connected to each other. If either type of crack is found, do not use the piston again.






Illustration 19 g01198626The light marks are caused by contact with the valves. Find the cause of the contact with the valve and then inspect the piston for cracks.

Illustration 20 g01198629The light marks are caused by contact with the valves. Correct the cause of the contact.

Illustration 21 g01198632The heavy marks are caused by contact with the valves. Correct the cause of the contact.






The latest designs of direct injection pistons have a sharp edge at the edge of the crater bowl in order to ensure good engine performance for emissions and fuel economy. Fine cracks can begin at this sharp edge due to thermal fatigue and mechanical fatigue. Although some fine cracking may be normal, severe cracks can be a sign of severe engine load factor. The pistons with crater cracks that are less than 6.00 mm (0.236 inch) long may be reused. The piston can be reused if the cracks are on the edge of the crater rim of the piston. The cracks in the piston should not be within 30 degrees of the centerline of the piston pin bore.

Illustration 22 g01198635The light marks are caused by contact with the valves. No material has been embedded into the surface of the piston. Check for cracks in the ring band area and measure the pin bores before reusing.

Illustration 23 g01198642Typical example of pitting

Illustration 24 g01198651The light pitting on the piston crown and in the area of the valve pockets is acceptable.



(1) The centerline of piston pin bore

(A) 30 degrees

(B) 6.00 mm (0.236 inch)


Illustration 25 g01198655Cracks that are less than 6.00 mm (0.236 inch) long are allowed within the shaded area.

Illustration 26 g01198667The cracks are in the crater area of a direct injection piston. Measure the length and angle of the crack in relation to the pin bore. Use the piston again if the crack is less than 6.00 mm (0.236 inch) wide and the crack is not within 30 degrees of the pin bore.

Illustration 27 g01198673The crack in the piston is outside of the allowable area for cracks.




Use the piston again after the raised edges are removed and the piston is cleaned and completely inspected.


Use the piston again after the raised areas have been cleaned. Use the piston after the areas have been completely inspected.

Pistons that have cracks in the area of the valve pockets should not be reused. The material that is below the valve pocket of the piston should not be removed. Do not remove any sharp edges or any other material that has been embedded in the piston that can be easily removed by hand.

Illustration 28 g01198681Remove burrs or raised edges with a file or a small grinder.

Illustration 29 g01198686Light damage to the edge of the piston crown.

Illustration 30 g01198701The damage is to the edge of the piston crown.




Use the piston again after the raised areas are removed and the area of the ring land is checked carefully.


Use the piston again after the raised areas have been removed and the area of the ring land is checked carefully.


Use the piston again after the raised edges or debris is removed with a file.

Illustration 31 g01198704The damage is to the edge of the piston crown.

Illustration 32 g01198777Arrow (A) shows a small chip on the top of the piston. Arrow (B) shows debris on top of the piston.

Illustration 33 g01198780The small holes (A) are caused by debris. Light pitting (B) in crater.







Illustration 34 g01198781There is light pitting in the area of the valve pocket.

Illustration 35 g01198785Do not reuse any piston that has heavy pitting on the entire crown.

Illustration 36 g01198788The light amount of erosion that is allowable






Illustration 37 g01198791The piston displays the maximum amount of erosion that is allowable. Do not reuse a piston that is displaying the severity of erosion that is more than the amount that is shown in Illustration 37.

Illustration 38 g01198792The piston has heavy erosion on the crown. Any piston that is displaying this severity of erosion anywhere on the crown should not be reused.

Illustration 39 g01198796The close up photo of a piston with heavy erosion




Pitting of the Piston Crown



Illustration 40 g01198805The heat plug is loose and uneven with the surface of the crater. If the plug requires tightening, do not reuse the piston.

Illustration 41 g01198814The piston crown is showing light pitting.

Illustration 42 g01198821The piston crown is showing light pitting.




Fuel Erosion The piston has erosion in the area of the crater that is caused by fuel. The erosion of the piston that is caused by fuel is only a problem of appearance and the structural integrity of the piston is not affected. Use the photos that follow to determine if the piston can be reused.



Illustration 43 g01198965The piston crown is showing numerous deep pits and distinct pits.

Illustration 44 g01198972The crater of the piston is showing light erosion that is caused by fuel.

Illustration 45 g01198977The crater of the piston is showing light erosion that is caused by fuel.




Do not use pistons that have more severe erosion than the piston that is shown.



Illustration 46 g01198982The crater of the piston is showing numerous areas of erosion that is caused by fuel.

Illustration 47 g01198986The crater of the piston shows deep erosion that is caused by fuel.

Illustration 48 g01198989The crater of the piston is showing six points of deep erosion that is caused by fuel.




Top of the Ring Land



Illustration 49 g01198990The crater of the piston is showing multiple points of deep erosion that is caused by fuel.

Illustration 50 g01199009The piston shows normal carbon scratches. The scratches are common on pistons with offset pin bores.

Illustration 51 g01199013Example of light carbon scratches on the piston





Use the piston again after the raised areas are removed with a file and the piston is properly cleaned. Refer to the Reuse and Salvage Guidelines, SEBF8059, "Procedures and Specifications to Clean and Measure Pistons".



Illustration 52 g01199018The piston is displaying heavy carbon scratches in the top ring land.

Illustration 53 g01199021The piston has light carbon scratches in the top ring land.

Illustration 54 g01199026Deep scratches on the piston which have offset pin bores.



Note: If an engine failure has caused a force against the piston, the piston must be visually inspected for cracks. Refer to Illustrations 55, 63, and 77.




Illustration 55 g01199027A crack in the top land of the piston

Illustration 56 g01199028Minor damage to the top lands of the piston

Illustration 57 g01199038Minor damage to the top land of the piston





Ring Band, Ring Grooves and Ring Land



Illustration 58 g01199084The piston is showing separation of the ring band. Check below the ring band and above the ring band. The piston is not reusable if there is the slightest separation in the ring band.

Illustration 59 g01199093The piston has had pieces that are broken out of the top land and the ring band.

Illustration 60 g01199096A chip in the oil control ring groove




Note: The piston can be reused after a burr or a raised area is made smooth with a file.


Use the piston after the carbon deposits are removed. Refer to the Reuse and Salvage Guidelines, SEBF8059, "Procedures and Specifications to Clean and Measure Pistons".


Illustration 61 g01199148Carbon in the ring grooves of the piston

Illustration 62 g01199152Damage to the piston groove







Procedure to Inspect Skirt

The crack is in the ring land of the piston.

Illustration 64 g01199167The damage is to the ring land of the piston.

Illustration 65 g01199168The damage is to the ring land of the piston. The piston is not reusable as the ring lands have been compressed. Filing the area smooth will not make this piston reusable.

Illustration 66 g01199171An example of a piston with normal wear on the skirt. The area that is gray has many small scratches.




Use the piston again after the scratches are removed by cleaning with glass beads. Refer to the Reuse and Salvage Guidelines, SEBF8059, "Procedures and Specifications to Clean and Measure Pistons".


Use the piston again after the scratches are removed by cleaning with glass beads. Refer to the Reuse and Salvage Guidelines, SEBF8059, "Procedures and Specifications to Clean and Measure Pistons".


Illustration 67 g01199282A piston that has light scratches on the skirt

Illustration 68 g01199285The piston skirt is from a 3500 series engine that has been cleaned per the guideline the Reuse and Salvage Guidelines, SEBF8059, "Procedures and Specifications to Clean and Measure Pistons". The piston skirt still has light scratches but there is no raised material.






Use the piston again after the skirt has been cleaned and inspected. Refer to the Reuse and Salvage Guidelines, SEBF8059, "Procedures and Specifications to Clean and Measure Pistons".


Do not use the piston again unless the particles can be removed by cleaning with glass beads. Refer to the Reuse and Salvage Guidelines, SEBF8059, "Procedures and Specifications to Clean and Measure Pistons".

The piston is showing evidence of seizure. The piston has more damage that is suggested so the piston should not be reused.

Illustration 70 g01199297The piston shows scuffing just below the bottom ring groove.

Illustration 71 g01199299The piston shows small shiny areas of particles or aluminum bearing material that have been embedded in the skirt.






The piston can be reused if there is no raised material or embedded material in the skirt after being cleaned.


Illustration 72 g01199304The piston shows metal particles in the skirt. The piston has dark particles that are not aluminum so the piston should not be reused.

Illustration 73 g01199310The piston is showing the maximum amount of damage to the skirt that is possible. A piston must have no raised material in order to be reused.

Illustration 74 g01199315The piston displays wear due to lack of lubrication for a short period of time.

Illustration 75 g01199316The piston is showing damage just below the ring groove. The piston has no cracks that are visible.



Use the piston again after the raised material is removed with a file and the piston is clean. Refer to the Reuse and Salvage Guidelines, SEBF8059, "Procedures and Specifications to Clean and Measure Pistons".




Note: Illustrations 78 and 79 are displaying a crack in the piston skirt of a C15 piston. The piston skirt that is shown in Illustration 78 and Illustration 79 is the same piston.

Illustration 76 g01199329A piston that has light damage to the bottom of the skirt

Illustration 77 g01199333The piston is showing heavy damage to the skirt. A piston with cracks in any area of the skirt make the piston unusable.






Graphite Coated Pistons If a piston has severe scoring, material transfer, embedded material, or other obvious damage the piston should not be used again.


If the cover plates of the cooling gallery are found in a loose condition the piston should not be used again.


The C15 piston is showing damage to the piston skirt. There is a crack near the hole for the pin.

Illustration 79 g01243598The location of the vertical line is at the transition line of the piston skirt.


Illustration 81 g01199395The piston has minor scratches in the graphite coating of the skirt.





Use the piston again if the loss of coating on the skirt does not exceed half the area of the skirt. The piston should not be reused if the wear is from hard contact.


Use the piston again if the loss of coating of graphite does not exceed half the area of the piston skirt. The piston must also show no signs of wear from hard contact.

Illustration 82 g01199403The piston has minor scratches in the coating of graphite on the skirt.

Illustration 83 g01199408The piston has loss on the coating of graphite on the skirt.





The loss on the coating of graphite on the piston exceeds half of the skirt. The piston is also showing signs of wear from hard contact.


The loss on the coating of graphite on the piston exceeds half of the skirt.




Illustration 87 g01199571The piston should not be reused because of scratches that extend into the steel skirt.




Procedure to Inspect Pin Bores During the visual inspection of the piston pin bore, carefully inspect the snap ring groove of the piston for damage or wear. Do not use the piston again if the groove is excessively worn or damaged. The piston should be checked in the snap ring groove for undetected wear by making a comparison between the fit of the snap ring in the old piston and fit of the snap ring in a new piston. The piston should not be reused if the effort to turn the snap ring in the used piston is significantly less than the new piston.



Illustration 88 g01199573The scratches on the piston that extend into the steel skirt that can be felt should not be used again.

Illustration 89 g01199576A piston with light damage to the pin bore and skirt







Illustration 90 g01199578A piston with damage to the snap ring groove

Illustration 91 g01199581The piston has internal damage to the area of the piston pin bore.

Illustration 92 g01199584The piston has light wear on the edge of the bore, but the measurements of the bore are correct.

Illustration 93 g01199614The piston has discoloration on the underneath side. Measure the piston pin bores in order to make sure that there is no distortion.




Do not use the piston again if the scratches can be felt with a fingernail.



Illustration 94 g01199941The piston has a wear pattern inside the pin bore.

Illustration 95 g01199944The piston shows wear and scratches in the pin bore that can be felt with a fingernail.

Illustration 96 g01199956There is a track of heavy debris on the piston. The piston pin bore can be used again because the surface of the bore is smooth.






Illustration 97 g01199959There is embedded debris in the surface of the piston. The piston has debris that can be felt.

Illustration 98 g01199964The piston has visible scratches that cannot be felt. The surface of the piston is smooth.

Illustration 99 g01199969The piston has visible scratches and a track of debris that cannot be felt. The surface of the piston is smooth.






Piston Pin Bores

Illustration 100 g01199975The piston has visible scratches that can be seen but not felt. The scratches on the piston have been caused by removing and installing the pin.

Illustration 101 g01200089The piston bore has a maximum allowable amount of debris.

Illustration 102 g01200090The piston has severe tracks of debris but the surface of the bore is smooth.





Illustration 103 g01200091The piston has impact damage that was caused by mishandling. This type of damage to the piston will result in a crack that will extend to the bore.

Illustration 104 g01200093The piston shows a wear step in the snap ring groove. This type of damage is caused by a rotating snap ring.





Two-Piece Pistons

Nomenclature

Reconditioning Procedure

There are several methods for reconditioning minor damage to the piston crown and the piston skirt. Use the method for cleaning that is least aggressive during the process for reconditioning of the piston.

A depression results when a part is scratched, nicked, or dented. The scratch, the nick, or the dent can also result in a area that is raised.

The piston has damage that has been caused by snap ring pliers during the removal of the snap ring.

Illustration 106 g01200097The schematic of a two-piece piston crown and piston skirt

(1) Crown

(2) Crater

(3) Ring Grooves

(4) Ring Lands

(5) Piston Pin Bushing

(6) Skirt

(7) Pin Bore in Skirt

(8) Top Land

(9) Piston Side Relief



The raised areas of the piston can be removed by several methods. The most common methods of removing raised metal are a file, a polishing wheel, or a Scotch-Brite abrasive disc. The file is the most aggressive method for removing raised material. The file is generally recommended for small areas on the surface for material that has been raised more than 0.20 mm (0.008 inch). Use caution to ensure that only the raised material is removed. Be sure that no indentations are left behind from the reconditioning procedure.

The polishing wheel and the Scotch-Brite abrasive disc are used to remove small scratches in larger areas. The piston skirt is made from aluminum. In order to reduce the risk of damage to the piston, manual buffing is preferred to a polishing wheel to remove scratches and imperfections. Illustration 132 shows an example of a skirt that was buffed with a Scotch-Brite abrasive disc.

Visual Inspection

Make a basic visual inspection of the piston before cleaning. Check the piston for obvious damage. Do not use the piston again if obvious damage is visually inspected. Clean the piston and inspect the piston if no damage is observed.

Handling Damage and Cracking


The piston may be used again if the raised material can be removed with a file or an oilstone.

Illustration 107 g01200111Carefully remove the raised metal area that is caused by nicks, dents and scratches. Illustration 107 shows examples of the various types of damage to the piston. In order for the piston to be reused, the piston must be cleaned and the area of metal that is raised must be removed from the surface of the piston.

(A) Scratch

(B) Raised Metal

Illustration 108 g01200118The piston skirt has dents in the bottom.




Use the piston again after removing the raised material.


Use the piston again after removing the raised material.


Illustration 109 g01201901The piston has several small nicks that appear as shiny areas.

Illustration 110 g01201911The piston has several small nicks that are visible.

Illustration 111 g01201914The piston has a crack in the web area. There is also damage near the pin bore of the piston.






Illustration 112 g01201921The piston has damage in the area of the pin bore. There is no amount of damage that is allowable in the area of the pin bore.

Illustration 113 g01201926The piston has a large nick on the surface of the skirt. The damage to the skirt is not repairable.

Illustration 114 g01201932The piston has a nick that is too large to repair.





Scuffing

Scuffing is not permitted on the piston skirts that are going to be reused. Scuffing is a combination of scratching and embedded material. Do not reuse skirts that have evidence of scuffing.


Illustration 115 g01201935The piston has an area of damage that is too large to repair.

Illustration 116 g01201938The piston has damage to the top surface of the skirt. The piston must not have damage in the joint between the skirt and the crown.

Illustration 117 g01201941The piston has a scuffed area that is small and material is also embedded in the surface.






Illustration 118 g01201951The piston has a scuffed area that is small and material is also embedded in the surface.

Illustration 119 g01201960A piston that has moderate scuffing

Illustration 120 g01201967The piston has moderate scuffing.




Discoloration and Markings


Use the piston again after the scratches have been polished.


Illustration 121 g01201972The piston has severe scuffing.

Illustration 122 g01201974The piston has a horizontal marking that is discolored. The horizontal marking does not affect the reusability of the piston.

Illustration 123 g01201978The piston has discoloration due to the cleaning solution.





Use the piston again after polishing the skirt to remove the corrosion. There must also be no corrosion in the piston pin bore or in the groove for the piston snap ring.

Embedded Material

There must be no embedded material in the piston. Embedded material can appear as dark hard particles in the surface of the skirt that can scratch the cylinder wall. Embedded material can also appear as light particles on a dark piston. Do not reuse any piston skirt that has embedded material.

Illustration 124 g01201990The piston has horizontal markings that are the result of the manufacturing process. The horizontal markings are not a defect on the piston.

Illustration 125 g01201992The piston is showing corrosion that is the color of rust.





Note: The piston skirt that is shown in Illustration 132 has scratches that can be smoothed through buffing. The piston skirt has embedded material so the skirt cannot be reused.



Scratches

Even small amounts of embedded material are unacceptable.

Illustration 127 g01201997The piston has a large embedded particle which makes the piston unacceptable.

Illustration 128 g01202022The piston shows a heavy concentration of embedded particles.





The piston can be used again after the piston is smooth from buffing.


Use the piston again after the piston is smooth from buffing.


Use the piston again after the piston is smooth from buffing.

The piston has scratches that are not deep and no embedded material is visible.

Illustration 130 g01202026The piston has scratches that are not deep and no embedded material is visible.

Illustration 131 g01202028The piston skirt is showing scratches that cover a wide area but the scratches are not deep.





Use the piston again if all the raised material is removed by buffing.


Use the piston again if there is no visible raised material or embedded material.


Use the piston again if there is no visible raised material or embedded material.

The piston has a skirt that is smooth from buffing with a Scotch-Brite abrasive disc.

Illustration 133 g01202296The piston may have scratches that are too deep to salvage. The piston needs to be buffed and the piston needs to be inspected before the piston can be reused.

Illustration 134 g01202297The piston may have scratches that are too deep to salvage. The piston needs to be buffed and the piston needs to be inspected before the piston can be reused.





Crowns

The recommendations in this section are based on two-piece piston crowns. To illustrate damage to pistons, some of the photographs in this section are of one-piece pistons.


The piston can be used again if the raised material can be removed with a file or oilstone.


The piston may have small scratches but embedded material is visible.

Illustration 136 g01202305The piston has damage in the areas between the lands. The piston can be reused because the damage does not extend into the ring groove.

Illustration 137 g01202308The damage to the piston extends into the area of the ring groove which cannot be corrected.






Do not use the piston again if the damage to the ring land is by the piston ring that will affect the shape of the groove.

Illustration 138 g01202310The damage to the piston is in the area of the ring groove which cannot be corrected.

Illustration 139 g01202331The damage to the piston is on the bottom of the crown which cannot be repaired.

Illustration 140 g01202333The piston has porosity in the bottom of the ring land that does not affect the sealing ability of the ring. Notice the dent at the top of the piston crown. The piston can be reused after the raised material is removed.

Illustration 141 g01202335The piston has a dent between the ring grooves that can cause the groove to change in shape.






Illustration 142 g01202339The piston has a dent between the ring grooves that can cause the groove to change in shape.

Illustration 143 g01202340The piston has damage inside the ring groove.

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visual inspection of the piston

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