By measuring the resistance of the starter motor.
How to perform the test;
Disable the engines fuel injection system.
Using a Engine diagnostic Oscilloscope ( preferably a four channel one ) connect the high amp clamp to channel A.
Select the highest range and zero the clamp.
Connect the clamp to either the positive or negative battery
By looking in your waveform library you will see the correct waveform pattern for the actual engine and model you are testing for 100% correctly displayed compressions waveform.
Start the Scope. ( i.e. The Oscilloscope )
Crank the engine for around five seconds to capture the waveform displayed.
Use the Waveform Buffer, Zoom and Measurements tools in the Scope to examine/ expand etc the pattern displayed.
The orientation of the clamp relative to the wire will determine whether it has a positive or negative output.
Should the waveform be inverted then reverse the clamp orientation to correct it.
This test uses the following property of a DC starter motor to provide a convenient non envasive comparison of engine cylinder compressions.
With a fixed supply voltage the current drawn by a DC starter motor is proportional to the load on the motor, when the load increases the current drawn therefore increases.
During the engine cranking both the starter motor's load and current increase as each piston travels through its compression stroke.
Therefore, a continuous measurement of starter motor current indicates the relative degree of compression across the cylinders as they cycle through in their firing order.
Ideally of course the measured cylinder compressions and the indicated associated current draw would be equal but in reality even on a good engine there will be some slight variations displayed.
A repetitive low peak in the waveform indicates a cylinder waveform which will display that cylinder low compressions and will therefore require further investigation.
Compression related issues can cause poor running , misfires and emission related symptoms.
Typical faults causing compression losses are,
Inlet / exhaust valve problems.
Piston/bore and/or compression ring faults.
Blocked air intakes.
Head gasket leakages.
Cylinder bore washing .
See the sawtooth type patterns typically displayed for a good engine waveform pattern.
Note the high initial high kick up Amps displayed, the current then falls and stabilises to form a uniformly repeating waveform pattern as the engine continues to crank.
Note the waveform troughs which indicate no repetitive anomalies.
So all you folk out there who still believe in the white metal bearing scraper, the flogging spanners and all torque settings should be F.T. its time to draw out, buy yourself a decent Scope and get on this crazy roundabout of modern, up to date engine diagnostic problem sorting.
Then you will have completed the test in full by the time your colleague is still trying to get that seized no one pencil injector out of the head!
In conclusion not having heard anything whatsoever from the originator of this post I can only conclude that by adjusting all tappets correctly that tight one or both exhaust valves have cured the problem.
Wonder if we will all be put out of our nightmare scenario and get this confirmed?
Over to you Rohanmariner.
So the way to measure compressions in a Diesel engine with electric start with NO dismantling whatsoever?
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.