Author Topic: Compression Test  (Read 1612 times)

Offline Scott M

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Compression Test
« 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
« Last Edit: February 27, 2017, 04:54:50 PM by Scott M »
78 GMC K25 4x4 - Beach Toy
6in Suspension 2in Body
Zero Rates Upfront
ZZ4/TH400/NP203
46" Military XMLs

Offline VileZambonie

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Re: Compression Test
« Reply #1 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?
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Scott M

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Re: Compression Test
« Reply #2 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?  :-[
78 GMC K25 4x4 - Beach Toy
6in Suspension 2in Body
Zero Rates Upfront
ZZ4/TH400/NP203
46" Military XMLs

Offline VileZambonie

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Re: Compression Test
« Reply #3 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.
,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Scott M

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Re: Compression Test
« Reply #4 on: February 28, 2017, 01:32:40 PM »
Okay will do, i appreciate the help! Ill look into the starter as well
78 GMC K25 4x4 - Beach Toy
6in Suspension 2in Body
Zero Rates Upfront
ZZ4/TH400/NP203
46" Military XMLs