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07-22-2017
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#1 |
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Join Date: Jun 2006
Location: Sparks, NV
Posts: 2,843
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Compression test Lesson
So... shortly after I bought my latest 90' Z in June I bought a new compression tester kit at Harbor Freight. I already had one an old one, a Sun Equipment brand, but I wanted one with a check valve and pressure relief. I always had good luck with the Harbor Freight stuff so I got one of their better kits.
I tested the compression on the new Z shortly after I got it and found the readings around 150lbs but steady across all cylinders. While not happy about the readings I was not surprised as the car has 180k miles and I'm at almost 5000ft altitude. LGAFF suggested I do some intake de-carbonizing and possibly it should pick up some compression. So to start I did 2 rounds of Sea Foam spray directly into the intake. Thought it felt better afterwards. Today I decided to run another compression test and see what if anything happened. Last time with the new tester I had trouble getting the fitting seated in the #8 cylinder. So I decided to start with #8 and use my old tester that has a slimmer hose. Ran the test and was shocked to get a reading of 195! Hmmm...  so I ran #7 with both testers. 195 with the Sun tester, 150 with the Harbor Freight? Ended up running all the cylinders both ways and got the same result. The Sun tester has all cylinders in the 190 to 195 range and the Harbor Freight in the 145 to 150 range. The old Sun tester has always been accurate. So I got on the Harbor Freight web site and checked the reviews for the compression tester. Guess what, numerous complaints about the testers running 20 - 40 lbs low. One guy even rebuilt his snow mobile engine only to find out the tester was wrong. So tomorrow the tester goes back to Harbor Freight, I'll stop a Summit Racing down the street and pick a new one with the features I want. And... most importantly I'm jazzed that my 180k mile Z has surprisingly good compression. 195 corrected for altitude puts it in the 210 to 215 range at sea level.  As for Harbor Freight, still good for hand tools, some specialty tools and supplies. Probably not so good for the more sophisticated stuff. If you can call a compression tester sophisticated... lesson learned. H 
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07-23-2017
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#2 |
 Join Date: May 2009
Location: Sparks, Nevada
Posts: 40
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Re: Compression test Lesson
Hans, i might buy a Harbor freight item if i will use it a fee times. But usually if critical measurement is needed i would use a better quality tool.
Sent from my SAMSUNG-SM-G930A using ZR-1 Net Registry mobile app |
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07-23-2017
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#3 |
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Join Date: Jan 2017
Location: US
Posts: 233
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Re: Compression test Lesson
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07-23-2017
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#4 |
 
Join Date: Mar 2007
Location: Crystal Lake, IL
Posts: 7,180
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Re: Compression test Lesson
Sweet!
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LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359 |
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07-23-2017
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#5 |
Join Date: Nov 2007
Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri
Posts: 6,466
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Re: Compression test Lesson
HATE IT WHEN THAT HAPPENS!
Compression test a few months ago, 1-3-5-7-2-4-220 psi+/- 6=180, 8=165 😲 WTH! Auto Zone compression testor seal went bad! Bought what I hope now is a good one. Thing is, i was looking for a blown head gasket - and my heart sank when i thought I'd found one. Cant imagine how happy I was to discover a bad seal on the compression test gauge. Turned out to be something simple insread! Last edited by Paul Workman; 07-23-2017 at 09:06 PM. |
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07-25-2017
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#6 |
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Join Date: Jun 2006
Location: Sparks, NV
Posts: 2,843
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Re: Compression test Lesson
Confirmed! Got the new compression gauge, it confirmed the higher 190-195 readings of the old Sun gauge I had. Looks like this engine is pretty solid for 180k miles
On a side note, I took the Harbor Freight gauge back and since I didn't have the receipt (CRS on my part) they exchanged for a new one. Well, the new one is bad too. Exactly the same as the first one. Oh well, I'm sure they'll exchange it for something else I can use... H
Last edited by Ccmano; 07-25-2017 at 03:04 PM. |
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07-25-2017
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#7 | |
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Join Date: Nov 2007
Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri
Posts: 6,466
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Re: Compression test Lesson
Quote:
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07-25-2017
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#8 | |
Join Date: Jul 2007
Location: Bartlett, IL
Posts: 7,157
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Re: Compression test Lesson
Quote:
At least we know the gauges are consistent.lol Sent from my iPhone using ZR-1 Net Registry
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1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Flowmaster Cats - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Shelby Series 1 - Wilwood Brakes Custom Interior NCM Lifetime Member #978 |
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07-25-2017
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#9 | |
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Join Date: Jun 2006
Location: Sparks, NV
Posts: 2,843
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Re: Compression test Lesson
Quote:
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07-25-2017
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#10 |
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Join Date: Jun 2006
Location: Sparks, NV
Posts: 2,843
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Re: Compression test Lesson
To be fair, in general I am not displeased with the things I have gotten a Harbor Freight. Everything has done its job satisfactorally. Certainly not top quality tools but for people who do just occasional work, a good alternative. This is really the first time I can think of that I have had this kind of problem. If I were a professional technician it would be a different story. Like I said lesson learned....
H
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