Question about Compression Test and Spark Plug Removal

[ScortLX]

Hello everyone. I'm doing a compression test on my '02 GT to double check and make sure the motor is ok (73K miles) for the 2.1L KB i have planned for it in a couple of months. Quick question though. An overwhelming majority of people say that compression tests should be done with the motor at operating temperature. People also say that we should never remove the spark plugs in a 4.6 unless the motor is COLD. So in order to do the test, should I just run the motor to operating temperature and just be super careful taking the plugs out? Or should I just take them out when the motor is cold and just do the compression test when the motor is cold. It just seems like a can't win situation with how each step is supposed to be done. Any help would be great. Thanks!

 

[wmburns]

Here's my take. The numbers from a compression test can be used in two ways. One way is to compare to other motors with a similar set up. In this case, the operational temperature can make some difference in the numbers.

The other way is the use the numbers in a relative way to compare cylinder to cylinder. In this case, the numbers have more meaning as they releate to the other cylinders in the same motor. In this case, it is more important to test each cylinder in the same way (IE same throttle setting, at TDC and same temperature).

Frankly, I thought the thing about removing spark plugs at a certain temperature applied to the 3 valve heads. But the 3V spark plug is a different thing all of it's own. Never remove a 3v spark plug without throughly understanding the procedure and following it exactly.

For what it is worth, I removed spark plugs with the motor COLD tons of times. Now, I do use anti-seize and a torque wrench to re-install.

So how about splitting the difference and doing it WARM?

Remember to throughly clean the spark plug wells before removing the spark plugs. Very important.

 

[the98stang]

also, if you use antiseize use VERY little, and torque all plugs to 14ft lbs!

compression should be within 10% of eachother.

 

[ScortLX]

So I got it all done finally. Compression test is done and there are new TR-6's in the stock plug's places. Compression came out as 150-153 over all cylinders and I'm very happy with that. It has 73K miles on it, but I wanted to check anyway. Now shes ready for boost in a few months! Figured I would post the results. Thanks for everyones help.

 

[GDawg]

Based on what you just published. Compression looks fine.

 

[Kilgore Trout]

The TR6 is a great choice for plug. However, they will need to be replaced in 12-18 months or so.

 

[ScortLX]

Yeah, I was happy with how the results came out. Should be good to go. I'll make sure I check the plugs often then. I have only driven the car 2K to 3K miles a year for the last few, so the plugs may last decently long. I was very paranoid when switching out the plugs. There weren't any big objects in the spark plug wells, but there was some kind of black kind of oily chunks that are still in the well after I swapped the plugs that couldn't be blown on vacuumed out. As long as nothing like rocks or other large debris fell in I should be ok right?