How To Do a Compression Test on an Engine

By | August 3, 2020

How To Do a Compression Test
Doing a compression test is an easy task for a DIY mechanic and can show if you have bad piston rings or valves.

Bad rings or valves can cause a leak to occur around them which instead of sending a piston downward the air goes around the piston.

This will give an engine a lack of power and need new rings and possibly valves.

The first step to finding out if it is the rings or vales that need to be replaced is to do a dry and wet compression test.

Tools Needed

  • Engine Compression Tester
  • Spark Plug Removal Wrench
  • Small Amount of engine Oil

Example Engine Compression Tester on Amazon
BETOOLL HW0130 8pcs Petrol Engine Cylinder Compression Tester Kit Automotive Tool Gauge

How To Do a Compression Test on an Engine

  1. Remove the spark plug on the cylinder to be tested.
  2. Insert the Compression Tester Tool.
  3. How To Do a Compression Test Step 1

  4. Turn the engine over 7-8 times and record the pressure.
  5. Remove the Compression Tester Tool and insert roughly 10cc of engine oil into the cylinder.
  6. Insert the Compression Tester Tool again.
  7. Turn the engine over 7-8 times and record the pressure again.
  8. Do I Have Bad Valves or Bad Piston Rings Compression Test Wet

Bad Rings or Valves?

  • If the Compression goes up the rings are leaking.
  • If the Compression stays the same the valves are leaking.

Doing an engine compression while simple can give a lot of information.

Knowing if the engine has bad valves or bad rings can save a lot of time and money before starting a tare down.

If the rings are worn and gone bad they will need to be replaced and often send white smoke out the exhaust.

A compression test may be old school but is a tried method that works.



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