Compression test results - good or bad??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

don t. - 72gmc · 06-11-2002, 02:05 PM

A guy at work loaned me his tester. I did a dry, then wet test.
I have no idea if this is good/bad. Im not having any (major) problems. Figured I'd ask the experts.
Did each cylinder 3 times, cranked over 5 times each time. Did all dry, then started back at #1 w/the wet test. Truck has been sitting for 3 days prior to test.
Watchya think????

1 - dry=130/130/130..wet=140/130/130
2 - dry=135/130/130..wet=130/130/130
3 - dry=135/135/135..wet=135/135/135
4 - dry=135/140/140..wet=140/135/135
5 - dry=135/135/135..wet=140/135/135
6 - dry=120/115/115..wet=115/115/115
7 - dry=135/130/130..wet=140/135/135
8 - dry=130/130/130..wet=135/135/135

Thanks...don t. ....

Mike C · 06-11-2002, 02:11 PM

It has worn very consistently and the rings appear to be in good shape. Looks like you may have a leaky valve on that one cylinder.

tom hand · 06-11-2002, 02:20 PM

I would say there is no problem. Sounds a little low but that could just be the guage. The biggest thing you look for in a compression test is difference. If the motor was worn out the numbers would be all over the place.

**COBALT** · 06-11-2002, 04:30 PM

Since I'm a complete knob sometimes, and I've never done a compression test (wet, dry, windy, snowy, or sunny - lol) how do you do one? What kind of guage do you need to get, and how does it hook up?

Gordo · 06-11-2002, 04:39 PM

It's considered a healthy engine when they are within 10% of each other. #6 looks like a valve may be leaking (as stated earlier) but otherwise your in good shape. I would moniter that cylinder and test it again in a few K's.

don t. - 72gmc · 06-11-2002, 06:34 PM

New69...the guage I used was from SunTest. Those were the only words on it. The guy said he's had it for years, used it twice. It screwed into the spark plug hole. Take all plugs out, I also disconnected the coil bat wire to be safe. Had my kid hit the key for 5 revolutions, did this 3 times on each cylinder. Did all 8. Started back at #1 w/a teaspoon of new motor oil. Did it all over again. I really wanted to use it for my 9n tractor (which aint as good).

2 more questions for the board...
1 - would Marvel Mystery oil work/clean up the leaky valve?
2 - what should the specs be?

Thanks again.....don t. .....

**john** · 06-11-2002, 07:36 PM

You should have the throttle open when taking test,which might help your readings. If you have stock engine and comp. ratio those readings dont sound bad for a angine with some miles on it.

06-11-2002, 02:11 PM	#2
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,723	It has worn very consistently and the rings appear to be in good shape. Looks like you may have a leaky valve on that one cylinder. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

06-11-2002, 02:20 PM	#3
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	I would say there is no problem. Sounds a little low but that could just be the guage. The biggest thing you look for in a compression test is difference. If the motor was worn out the numbers would be all over the place. __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

06-11-2002, 04:30 PM	#4
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	Since I'm a complete knob sometimes, and I've never done a compression test (wet, dry, windy, snowy, or sunny - lol) how do you do one? What kind of guage do you need to get, and how does it hook up? __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

06-11-2002, 04:39 PM	#5
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	It's considered a healthy engine when they are within 10% of each other. #6 looks like a valve may be leaking (as stated earlier) but otherwise your in good shape. I would moniter that cylinder and test it again in a few K's. __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

06-11-2002, 07:36 PM	#7
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	comp test You should have the throttle open when taking test,which might help your readings. If you have stock engine and comp. ratio those readings dont sound bad for a angine with some miles on it. __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/

06-11-2002, 02:05 PM	#1
don t. - 72gmc Registered User Join Date: Dec 2001 Location: harvard, il. USA Posts: 389	Compression test results - good or bad??? A guy at work loaned me his tester. I did a dry, then wet test. I have no idea if this is good/bad. Im not having any (major) problems. Figured I'd ask the experts. Did each cylinder 3 times, cranked over 5 times each time. Did all dry, then started back at #1 w/the wet test. Truck has been sitting for 3 days prior to test. Watchya think???? 1 - dry=130/130/130..wet=140/130/130 2 - dry=135/130/130..wet=130/130/130 3 - dry=135/135/135..wet=135/135/135 4 - dry=135/140/140..wet=140/135/135 5 - dry=135/135/135..wet=140/135/135 6 - dry=120/115/115..wet=115/115/115 7 - dry=135/130/130..wet=140/135/135 8 - dry=130/130/130..wet=135/135/135 Thanks...don t. ....

06-11-2002, 06:34 PM	#6
don t. - 72gmc Registered User Join Date: Dec 2001 Location: harvard, il. USA Posts: 389	New69...the guage I used was from SunTest. Those were the only words on it. The guy said he's had it for years, used it twice. It screwed into the spark plug hole. Take all plugs out, I also disconnected the coil bat wire to be safe. Had my kid hit the key for 5 revolutions, did this 3 times on each cylinder. Did all 8. Started back at #1 w/a teaspoon of new motor oil. Did it all over again. I really wanted to use it for my 9n tractor (which aint as good). 2 more questions for the board... 1 - would Marvel Mystery oil work/clean up the leaky valve? 2 - what should the specs be? Thanks again.....don t. .....



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