Short Block Dis-assembly

Today I began work on the automotive engines unit the first thing I did was begin work on the short block.

Engine that was dismantled a mazda B6 from a 323

Measurement and Inspection of Pistons and Bore


Tools Used

• 12mm and 14mm socket and driver
• spanners
• Feeler Gauges
• Micrometer
• Bore Gauge
• Dial Test Indicator Gauge

Inspection:The inspection I did was of the pistons and bore to see if there was any damage to them. 

When examining the pistons and bores I was looking for different types of ware including scuffing and scoring. This is caused by the piston rubbing on the bore when the temperature rises until melting point then particles of metal begin to weld together causing scratching on the surface of the piston or on the surface of the bore. This can be caused by restrictions in the water jacket causing hot spots on the cylinder wall, Incorrect oil pressure, or the connecting rod being misaligned.

To repair this requires the piston rings being replaced if only minimal damage occurred.  or the bore re-honed if there was more extensive damage. The engine I was working on did not require this as it was in good order.

Dismantled Block

Pistons 
      

Measurement of Pistons

This was done with a micrometer by putting it around the piston skirt and the taking a reading from it. This is done to check if the piston has collapsed due to poor lubrication, Excessive RPM, or a defective piston. 

Tested Pistons were all within manufactures specification and no further work was needed. If there was a collapsed piston problem can be rectified by replacing the piston. 

Piston Rings


This was measured by removing the piston rings from all 4 pistons one at a time and then setting them in there bores and measuring the gap in the rings to check if they are the correct size for the bore. If there is no gap the ring will break causing scuffing to the cylinder bore or the rings will not seal properly causing loss of compression on compression stroke, or loss of gas pressure during power stroke. Effecting engine performance. 
On the engine I checked there were some rings which were the incorrect size because the gap was to large and they would need replacing if the engine was going to work efficiently.  


Bore


The cylinder bore was measured using a bore gauge set to 78mm. To measure the diameter of the bore for each cylinder for ware of the surface of the bore caused by the piston rings rubbing on the surface when dirt has been inducted into the combustion chamber, from the air filter. Causes loss of compression and power. Can be repaired by re-honing the bore. Tested engine bore was in good condition with no serious damage occurring.