Compression Testing of Internal Combustion Engines - Direct Compression and Differential Compression Testing

The testing of the performance of the internal combustion engine is an expensive business. However there are lots of simple tests that may be carried find out here now to approximate the engines performance. One such test is the compression check, performed using an inexpensive engine compression test kit.





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The the different parts of car internal combustion engines like all other engines will ultimately require replacing, as a result of general damage.
A simple test to gain access to the performance associated with an internal combustion engine is to check the engine compression.
This can instruct the condition with the piston rings and cylinders, or other components in charge of the engines compression.
This is definitely an article on internal combustion engines performance testing in particular engine compression testing equipment and techniques.
This is utilized mainly on small aero engines and the procedure is as follows:
The equipment consists of the following components:
How to Perform Differential Compression Testing
Engine cowlings, cooler baffles, as well as the spark plugs are removed from the engine.



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The adapter is screwed in to a spark plug hole and also the propeller is turned to place the piston inside cylinder being tested at the very top dead center position. This can be determined having a finger over the compression adapter by expecting the "puff" because the piston completes the compression stroke.
With the propeller secured from rotating in either direction, the hose from the tester is attached to the spark plug adapter and pressure is applied. The left-hand gauge ought to be adjusted to 80 PSI, along with the right-hand gauge will demonstrate the differential compression reading. It may be essential to slowly rock the propeller forwards and backwards slightly to 'set the rings."
Ideally the stress at the cylinder gauge should equal the stress at the regulator gauge. A reading of 60 PSI or above with the cylinder pressure gauge, however, is acceptable and is also noted as 60/80. Any reading recorded in the cylinder gauge under 60 PSI indicates leakage of air past the components of the engine (rings, valves, or a crack within the cylinder) and requires further investigation, although a minimal reading on its own is not sufficient reason for rejecting a cylinder. You need to discover where the air is going and also consider if the components are high time or if the engine has exhibited excessive oil consumption.
A system diagram of the differential compression tester and a compression test record card for the six cylinder engine are shown below. (Please go through the images to enlarge.)





We shall examine the strategy of direct compression testing of an gasoline (petrol) engine, using these sequence:
The spark plugs are then removed; be sure you mark the leads using their relevant cylinder numbers.
The fuel supply should also be isolated, as well as the gas pedal held down inside fully open position allowing maximum air in the engine when cranking over.
When moving the test equipment from your cylinder; release the air pressure by opening pressure relief valve on the gauge/adapter.
The ignition key is now replaced in the ignition switch.
Compression Test ' Dry Method
The compression adapter is screwed to the No.1 cylinder spark plug hole, and the engine cranked at least six revolutions by an assistant.
The maximum compression reading is recorded and the process is repeated for the rest of the cylinders.
Compression Test ' Wet Method
In this test handful of lube-oil (teaspoonful) is poured into the cylinders which in fact had the lowest readings in the dry compression test.
The engine is surrended, as well as the readings taken as before and recorded.
A system diagram of a direct compression tester, and a compression test record card for the four cylinder engine are shown below.

Generally the sources of low compression are broken/worn piston rings or scored cylinders, usually due to high mileage or not enough oil changes.
Many in years past, I was traveling from Belfast to Invergordon in Scotland, to consider a position as engineer with an Aluminum Smelter. I was driving a vintage Vauxhall Viva of 1962 vintage, and yes it was burning a great deal of oil.
I used several gallons of oil on that journey and when I had a chance to check the problem, I lifted your head off and lo and behold there were a hole in one from the pistons concerning the size of an penny. A new piston cured the problem and the old car did us for any few years, albeit the toolbox was always inside boot!



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Anyway, that is another source of loss of engine compression. Some other causes are listed below.
Differential Compression Test
Direct Compression Test
If the direct compression test indicates low compression in the engine, further investigation of the cause normally can only be achieved by stripping the engine.
There are numerous compression test machines available to the car maintenance person, for both the differential and direct compression methods. They are also compression test machines designed for diesel engines.
A selection of these is shown below, with a few descriptive notes and prices.
Direct Compression Test Kits
1. Petrol Engine Compression Test Kit 6 pc Sealey CT955


Specifications:
2. Actron CP7828 Professional Compression Tester with Storage Pouch



Specifications:
Differential Compression Test Kits
1. ATS Differential Cylinder Pressure Tester


Specification:
The above compression testers can be a selection that I have chosen due to their ease of use and price - motoring (or flying!) is costly enough and never have to purchase top in the range digital testers; the manual ones are simply as effective.
Please see the safety precautions in the operation manuals when purchasing a compression test kit, as these are very important on your safety. Some kits can be utilized without assistance, but it's much easier and best to have someone else to help you complete test.
Reference Webs:
1. Luscombe: Differential Compression Testing
2. Justoffbase: Petrol Engine Compression Test Kit
3. Mityvac: Basic Compression Test Kit
4. ATS: Differential Compression Kit
5. Youfixcars: Direct Compression Test Procedure