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To test compression, do i need to intall pushrods?

N

northernterritory

Member
[h=2]I want to do a compression test to see if the cylinder head job fixed my compression issue. If I am going to to have to remove the cylinder head, if the compression is not there, I would prefer to not waste time with installing the rest of the head. So, do I have to reinstall the push rods, set the valve clearance, and etcetera.[/h]
 
You do not need to install the valve train to test compression. If you have compression issues it will make it easier to do a leak down test to find of it is valves, rings or head gasket/warped head.
 
For future reference you should have performed a leak down before you took it apart. The compression test tells you if it’s bad but the leak down tells you where it is leaking.
 
You do not need to install the valve train to test compression.
Click to expand...

Ayuh,.... I have to disagree,.... If the valves don't open, 'n close, there'll be no compression to test,....
 
northernterritory said:
I want to do a compression test to see if the cylinder head job fixed my compression issue.
If I am going to to have to remove the cylinder head, if the compression is not there, I would prefer to not waste time with installing the rest of the head. So, do I have to reinstall the push rods, set the valve clearance, and etcetera.
Click to expand...

Although you do mention push rods, you have not mentioned which engine you are referring to!
Let's say that this is a V-engine with OHV system.

In order to check Compression, all valves must function...... i.e., both Intake and Exhaust.... and the cam followers must be adjusted correctly!

FYI: We DO NOT actually adjust valves...... we adjust the hydraulic cam follower's plunger depth.
If V-8, you'll do best if you follow the 8 stop static adjustment procedure!

So bottom line.... Yes, you will need to complete the installation, make the adjustments, etc, in order to take an accurate Compression Reading!


A cylinder-leak-down-test is performed in order to determine where a compression loss may be occurring.
The test is performed while the rotating assembly is static.


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What was the compression issue and what was fixed on the head ?------Did you find a " smoking gun " during the repair ?---If so the the compression will be OK again.
 
racerone said:
What was the compression issue and what was fixed on the head ?------Did you find a " smoking gun " during the repair ?---If so the the compression will be OK again.
Click to expand...

Not if the diagnosis was incorrect to begin with!
This is where the cylinder-leak-down-test will be helpful!


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racerone said:
I asked the original poster to provide information on what was observed / done during the repair of the head !!!!
Click to expand...

I fully understand!
However, if the diagnostics were incorrect and if any of the piston rings were bad, the cylinder head work may not be able to bring the cylinder pressures back to where they need to be.


In other words… Without having done a cylinder leak down test prior, the cylinder head work may prove to have been futile.

I do agree with you that would be helpful if the OP had given us more information!


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The original poster should state whether there was an issue with low compression on one cylinder or all !----Should state why cylinder head was removed and what work was needed to be done.----And what was found if only one cylinder had an issue.----The original post is very , very vague in my opinion.
 
Again, I'm with you..... more info would have been nice! However, the OP's question was answered. He asked; "So, do I have to reinstall the push rods, set the valve clearance, and etcetera?"
In other words...... he was wanting to know if the above work was necessary in order to perform a compression test.


It's very likely that he did end up installing his push rods and adjusted his cam followers. :D




.

 
He might also need to know the difference between doing a leak down compression test and a compression test using a pressure gauge. Most backyard mechanics would not have access to this specialized (not available at Autozone) tool.
Cheers,
Doug
 
Doug said:
He might also need to know the difference between doing a leak down compression test and a compression test using a pressure gauge. Most backyard mechanics would not have access to this specialized (not available at Autozone) tool.
Cheers,
Doug
Click to expand...

Doug, I agree, but let's not further confuse him!

1.... a compression test reveals how much pressure the engine's piston can create within it's cylinder. This is also known as a cylinder pressure test!
The gauge and hose that are used to measure the pressure are accumulative and require several compression cycles in order to give us an accurate reading.

2.... a cylinder-leak-down-test (quite different from that of a "Compression" test) allows us to see how well a cylinder is able to retain pressure. It is a test whereby a cylinder is pressurized with a controlled volume of air via a spark plug port. We then use two separate gauges to see what what pressure is entering the cylinder, and then what proportion of the compressed air is leaking, and at which area...... I.E., valve seats, head gasket, crack within cylinder head or piston rings.



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