Stupid question. Checking Compression.
05-03-2004, 04:13 AM
#7
3.0 BAR
Join Date: May 2003
Posts: 3,365
Re:Stupid question. Checking Compression.
According to all my chevy manuals for working on v8s, they recommend that you run the motor till normal operating temp, shut it down, remove all spark plugs, then start testing. Yes it does make a difference on my v8 versus pulling one plug out -> test -> replace plug -> move to number 2. I've ran all my 4 cylinders that way as well, get it warm, remove all 4.. test one at a time. Replace. Oh yeah, battery should be fully charged to ensure proper stroking.
I think I read compression whenever I tune that 350 motor up, seems like I "tune" that motor every other month... stupid edelbrock performer carb
Before you begin testing, be sure to disconnect the live wire on the distributor (or take out the coil), don't want to get shocked by one of the plug wire leads.
There are several signs you need to yield to when testing, normal compression builds smoothly and evenly.
Low compression on the first stroke with a very small climb in compression the following strokes means worn piston rings. If that is the case, squirt some oil in the cylinder and see if it peaks right up. If it does, bad rings.
Low compression on the first stroke then it stays down low means you have a valve train problem, cracked head, blown headgasket. There are other tests to run if that's the case, like if you are burning oil on startup = valve leaking, water out the tailpipe = head crack/head gasket bad. Bad compression between two cylinders usually is bad head gasket.
I doubt you will have built up carbon deposits, so it's not likely you're gonna see compression spikes.
Let me know if you need to know anything else.
oh yeah, don't forget to WEAR SAFETY GLASSES nothing like having a fine mist of 93 octane sprayed in your eyes from the cylinders that don't have spark plugs in them.
-ryan
I think I read compression whenever I tune that 350 motor up, seems like I "tune" that motor every other month... stupid edelbrock performer carb
Before you begin testing, be sure to disconnect the live wire on the distributor (or take out the coil), don't want to get shocked by one of the plug wire leads.
There are several signs you need to yield to when testing, normal compression builds smoothly and evenly.
Low compression on the first stroke with a very small climb in compression the following strokes means worn piston rings. If that is the case, squirt some oil in the cylinder and see if it peaks right up. If it does, bad rings.
Low compression on the first stroke then it stays down low means you have a valve train problem, cracked head, blown headgasket. There are other tests to run if that's the case, like if you are burning oil on startup = valve leaking, water out the tailpipe = head crack/head gasket bad. Bad compression between two cylinders usually is bad head gasket.
I doubt you will have built up carbon deposits, so it's not likely you're gonna see compression spikes.
Let me know if you need to know anything else.
oh yeah, don't forget to WEAR SAFETY GLASSES nothing like having a fine mist of 93 octane sprayed in your eyes from the cylinders that don't have spark plugs in them.
-ryan
05-03-2004, 01:26 PM
#8
3.0 BAR
Join Date: Feb 2003
Posts: 9,089
Re:Stupid question. Checking Compression.
Originally Posted by quadnie
oh yeah, don't forget to WEAR SAFETY GLASSES nothing like having a fine mist of 93 octane sprayed in your eyes from the cylinders that don't have spark plugs in them.
-ryan
-ryan
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