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Piston Protrusion: (0 Reviews)

The document discusses checking piston protrusion to identify bent or twisted connecting rods. Piston protrusion refers to how far the piston extends above the cylinder deck. The procedure uses a dial indicator to take two measurements of each piston's protrusion and average them, with readings lower than specification indicating a bent rod. The engine discussed has performance issues likely caused by bent rods from excessive diesel entering the cylinders and damaging pistons. Checking piston protrusion requires following workshop manual procedures to properly diagnose connecting rod and engine damage.

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xristina
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757 views2 pages

Piston Protrusion: (0 Reviews)

The document discusses checking piston protrusion to identify bent or twisted connecting rods. Piston protrusion refers to how far the piston extends above the cylinder deck. The procedure uses a dial indicator to take two measurements of each piston's protrusion and average them, with readings lower than specification indicating a bent rod. The engine discussed has performance issues likely caused by bent rods from excessive diesel entering the cylinders and damaging pistons. Checking piston protrusion requires following workshop manual procedures to properly diagnose connecting rod and engine damage.

Uploaded by

xristina
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
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Piston Protrusion

(0 reviews)

Piston protrusion is a term that refers to how high a piston crown travels
above the cylinder deck. There are several reasons for checking this
specification but here we want to identify bent or twisted connecting rods.
Pictured is a 6.4L PSD engine that has performance issues and low
compression in two cylinders related to a failed common rail fuel injection
system. The injectors in this engine have been known to stick open allowing
excessive amounts of diesel fuel to enter the combustion chamber which can
cause bent or twisted connecting rods that sometimes may not be easy to
identify by visual inspection alone.Bent or twisted connecting rods can cause
low compression and piston and cylinder wall damage. During the
disassembly of any engine it is important to identify the cause of a failure as
well as related damage. In this era where it is more common to repair
damaged engines with remanufactured assemblies than it is to repair them
with parts and make measurements, many technicians no longer acquire the
necessary measuring tools. This test however requires a dial indicator which
is still a commonly used measuring tool.With the cylinder heads off of the
engine the cylinder block deck and the piston crowns need to be cleaned
according to the proper procedures outlined in the service manual. For each
piston, two measurements will be taken along the wrist pin axis and then
averaged to obtain the actual piston protrusion.

Here is the procedure as outlined in the workshop manual:

 Zero the Dial Indicator Gauge with Holding Fixture on the crankcase deck surface.
 Position the Dial Indicator Gauge tip on the piston head at the 3 or 9 o'clock
position.
 Rotate the crankshaft to measure the maximum piston protrusion and record.
 Reposition the Dial Indicator Gauge tip onto the piston head at the opposite
position.
 Rotate the crankshaft to measure the maximum piston protrusion and record.
 Average the 2 readings.

If the average reading is lower than the specification, the piston is lower in the
bore than it should be. This indicates a bent or twisted connecting rod.

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