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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Scott M on February 27, 2017, 04:50:41 pm

Title: Compression Test
Post by: Scott M on February 27, 2017, 04:50:41 pm
I have a ZZ4 350. not the fast burn, the one with the l98 heads.

Question is I did a compression test while changing the spark plugs and the numbers i got back where:

180   176
182   178
178   200
172   180
PF     DF

Do i need to adjust the valves in order to fix the compression on that cylinder which was 200.  I do not know enough about any of this so I would be taking it in to the guy who rebuilt if a few thousand miles ago. At one point in time shortly after the rebuild I did mess with the arm nut on a couple cylinders but dont remember which one(s). I was under the impression that I had a loose arm but it turn out it was timing and pinging.

I know i am probably going to get the look of this guy is dumb and going to mess something up but I am just looking for guidance.

Edit: I am calling them the arm nut cause i dont have roller rockers they are the saddle looking rockers and I apologize for not knowing the proper name

Thanks,

Scott
Title: Re: Compression Test
Post by: VileZambonie on February 27, 2017, 05:51:19 pm
Explain how you did your compression test. Did you have a battery charger hooked up, all plugs removed, choke open, wide open throttle 3 compression strokes?
Title: Re: Compression Test
Post by: Scott M on February 28, 2017, 07:03:01 am
I feel so stupid cause I did not have all the plugs out, my choke is electric and didnt have a battery charger hooked up... I shouldnt have "ass"umed it was so easy and should have looked it up. I will retest and report back if this is proper procedure. Also I had a hard time cause my starter keep jumping off the flywheel if i tried cranking it over more than a couple of turns. is that normal?  :-[
Title: Re: Compression Test
Post by: VileZambonie on February 28, 2017, 11:45:57 am
No that's not normal. check that it is properly mounted and shimmed. Check the teeth on the flywheel.

 Unless the test is performed properly you will find very inaccurate and inconsistent readings.
Title: Re: Compression Test
Post by: Scott M on February 28, 2017, 01:32:40 pm
Okay will do, i appreciate the help! Ill look into the starter as well