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Matt J
Matt J, Chevy Technician
Category: Chevy
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Experience:  10+ years automotive tech, 5 years of experience in a GM dealer
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There a tool to check engine compression without the heads being

Customer Question

is there a tool to check engine compression without the heads being on the engine
Submitted: 4 years ago.
Category: Chevy
Expert:  david replied 4 years ago.
Hi thank you for your question hope this helps.

The tool you need is called an engine compression test kit. What this does is screws into the spark plug hole and as you crank over the engine the compression is read out on the compression gage.

This is what a compression test kit looks like.
graphic

 

  • Make sure the engine has been warmed up before beginning the test, to ensure that the oil has been warmed up. A cold engine will not test correctly.
  • Disable the ignition module or coil.
  • Insert the compression tester into one cylinder spark plug hole at a time.
  • Hold the throttle to full open position to ensure the engine gets adequate air intake.
  • Crank the engine continually for at least five to 10 full revolutions to obtain an accurate reading on the compression tester.
  • Record the reading for each cylinder. If any of them vary 10 percent or more from each other a problem may exist in one or more cylinders. If the variance is greater than 10 percent, specialized testing equipment may be required to fully diagnose the problem.
  • If all cylinder readings are within 10 percent of each other, no further testing is required and compression is considered optimal.

 



Hope this helps
Good luck
Customer: replied 4 years ago.

I have that tool. What I want to know is there another tool that can be sed to just check the pistons compression without the heads being in place. the heads are already removed. I want to make sure that I dont have a pistin or ring problem.

 

Customer: replied 4 years ago.

I have that tool. What I want to know is there another tool that can be used to just check the pistons compression without the heads being in place. the heads are already removed. I want to make sure that I dont have a pistin or ring problem.

 

Expert:  Matt J replied 4 years ago.

Hello my name is XXXXX XXXXX I will be more than happy to assist you.

 

The is no tool out there you can by to do what you want to do. The reason for this is different cylinder head can make different compressions.

 

Think of it this way take a metal plate and bolt it to the engine block over the cylinder. With at plate over the cylinder there is little to no room between the piston at the highest point and the plate. So when you try to crank the engine the compression will be so high it will blow the engine up at the weakest point or just stop.

 

With a cylinder head it has a dome so the air will compress in the area. Depending on how large or small the dome is will effect the compression.

 

Unless you have the exact same cylinder head or a plate made to the same size as the dome of your cylinder head then there is no way to check compression.

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Matt J
Matt J
Chevy Mechanic
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10+ years automotive tech, 5 years of experience in a GM dealer