Compression testing.

Author Topic: Compression testing.  (Read 495 times)

Offline 67vertman

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Compression testing.
« on: February 24, 2009 - 12:33:27 AM »
What is the proper way to check the compression on a motor that hasn’t been turned over in eight years?

Should I turn it over first for a few minutes to lube the rings?  Or, should I shoot some oil down the spark plug holes?

I plan on dry testing it twice and then wet testing it twice.



Ron - Born and raised in Southern California

I got the 1970 Cuda, but still need the hot blonde to ride shotgun!

First car -1969 Road Runner 383 4sp

Current ride - 1970 Barracuda 440-6 4 sp Dana 60  (4:10)




Offline 72bluNblu

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Re: Compression testing.
« Reply #1 on: February 24, 2009 - 01:41:42 AM »
The only way to get a proper compression reading is with a warm engine. Typically you want to start the engine, let it get up to temperature and then do the compression check.

Obviously if it hasn't been started in eight years you should oil the cylinders and valvetrain before you crank it over to keep it from trashing anything. Was the engine a runner 8 years ago? if it was, I'd do a full tune up and oil change, squirt some oil down the cylinders and on the valvetrain and see if it will run. You'll probably have to run the fuel supply out of a gas can since the lines and tank are full of bad gas or are fouled completely.

If running it isn't an option you'll still need to oil the cylinders and valvetrain, but you won't be able to get an accurate compression reading. The rings don't seat the same cold as they do warm, and oiling the cylinders will help even worn out rings, giving you a false high reading. Once the oil works past the rings, the rings will still be cold, giving you a false low reading...

Offline 67vertman

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Re: Compression testing.
« Reply #2 on: February 24, 2009 - 08:59:59 PM »
Yes it was running when parked.  I was planning on changing the oil and doing a tune up anyways, so I will do it before I check the compression.  Thanks for the tip on warming it up and the false readings when cold.  I wanted to check the compression before I spent a whole lot of money trying to make it a "true runner" again.

Looks like I get to have some fun this weekend.  :clapping:



Ron - Born and raised in Southern California

I got the 1970 Cuda, but still need the hot blonde to ride shotgun!

First car -1969 Road Runner 383 4sp

Current ride - 1970 Barracuda 440-6 4 sp Dana 60  (4:10)

wagesofsin

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Re: Compression testing.
« Reply #3 on: February 24, 2009 - 09:48:11 PM »
you should prime the oiling system before turning that thing over!!!

use a drill and drive the pump, dampen the cylinders with lube, then attempt to turn it over, otherwise compression may not be your only concern!!

Offline femtnmax

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Re: Compression testing.
« Reply #4 on: February 25, 2009 - 09:05:14 PM »
 :iagree:
Phil