Compression test Lesson - ZR-1 Net Registry Forums

Ccmano · 07-22-2017

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

Tony91 · 07-23-2017

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.

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ssrszz4 · 07-23-2017

Amen

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LGAFF · 07-23-2017

Sweet!

Paul Workman · 07-23-2017

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!

Ccmano · 07-25-2017

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

Paul Workman · 07-25-2017

Quote:

Originally Posted by Ccmano

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

Yeah...maybe a hammer...or a crowbar: something non-precise!

-=Jeff=- · 07-25-2017

Quote:

Originally Posted by Ccmano

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.

At least we know the gauges are consistent.lol

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Ccmano · 07-25-2017

Quote:

Originally Posted by Paul Workman

Yeah...maybe a hammer...or a crowbar: something non-precise!

Exactly!
H

Ccmano · 07-25-2017

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

07-22-2017	#1
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	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 __________________ 90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold.

07-23-2017	#2
Tony91 Join Date: May 2009 Location: Sparks, Nevada Posts: 41	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

07-23-2017	#3
ssrszz4 Join Date: Jan 2017 Location: US Posts: 233	Re: Compression test Lesson Amen Sent from my XT1585 using ZR-1 Net Registry mobile app

07-23-2017	#4
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,194	Re: Compression test Lesson Sweet! __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

07-23-2017	#5
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	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! __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry Last edited by Paul Workman; 07-23-2017 at 10:06 PM.

07-25-2017	#6
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	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 __________________ 90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold. Last edited by Ccmano; 07-25-2017 at 04:04 PM.

07-25-2017	#10
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	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 __________________ 90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold.