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06-10-2010, 05:34 PM
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#1
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Name: Fireman450
Title: Daring to be diffrent!!
Status: Not Here
Join Date: Nov 2007
Location: Edmonton , KY
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Posts: 1,606
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Compression test
i have a guys truck I am working on. Came in missing, popping, and blowing oil out the dip stick tube. Blue smoke out the exahaust. So I ran a compression test and found cyls 1/3/5 low(To me) and slow to respond, 2/4/6 were 50 to 75 psi higher. lowest was 370psi, Highest was 475psi.
What i need to findout is what is normal compresstion, and when to reccamend a rebuild?
Thanks
Lynn
__________________
Lynn Chapman
Driver: 04.5 CR
Play Toy:1994 Dodge 12V, SMOKE SHOWIN! 2WD Pulling Team. vs. 3.0 in progress. Thanks to Northeast Diesel, MUMAU DIESEL , PullTech Chassis & Fab, Cooper High Performance, SKPP, Joe Gibbs Racing/Driven Racing Oils and all my friends and family!
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06-11-2010, 05:27 AM
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#2
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Name: Knuckledragger
Title: Knuckledragger
Status: Not Here
Join Date: Jun 2009
Location: Mt. Vernon, IN
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Posts: 236
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i dont know the normal compression but the numbers you got are to far apart. if i were to recomend a rebuild , it would be now.
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06-11-2010, 11:33 AM
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#3
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Name: mondtster
Title: Too Much Time
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Join Date: Jan 2009
Location: k74
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Posts: 1,206
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Quote:
Originally Posted by stock600
Do your self a favor and toss the comp. gauge and leak it down instead, then you will not only know what was hurt but also whats going on with the valve job while the head is off.
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x2...
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06-11-2010, 11:51 AM
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#4
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Name: Fireman450
Title: Daring to be diffrent!!
Status: Not Here
Join Date: Nov 2007
Location: Edmonton , KY
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Posts: 1,606
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Quote:
Originally Posted by stock600
Do your self a favor and toss the comp. gauge and leak it down instead, then you will not only know what was hurt but also whats going on with the valve job while the head is off.
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Care to elaborate on this? How does one properly perform a leak down test?
Thanks
Lynn
__________________
Lynn Chapman
Driver: 04.5 CR
Play Toy:1994 Dodge 12V, SMOKE SHOWIN! 2WD Pulling Team. vs. 3.0 in progress. Thanks to Northeast Diesel, MUMAU DIESEL , PullTech Chassis & Fab, Cooper High Performance, SKPP, Joe Gibbs Racing/Driven Racing Oils and all my friends and family!
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06-11-2010, 12:48 PM
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#5
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Name: Knuckledragger
Title: Knuckledragger
Status: Not Here
Join Date: Jun 2009
Location: Mt. Vernon, IN
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Posts: 236
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put about 120 - 150lbs of shop air on each cylinder with a gauge and ball valve inline. air the cylinder up and how fast the air leaks off. if you have the intake and exhaust off, you can listen for air bypassing the valves. i always use about 800psi of nitrogen on big engines. if you have a nitrogen bottle around and can plumb it up, i would use it.
Last edited by Knuckledragger; 06-11-2010 at 12:59 PM.
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06-11-2010, 12:58 PM
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#6
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Name: BgBlDodge
Title: Hates hippies
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Location: Buda, Tx
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My engine on compression was 475-500 on all 6.
__________________
2003 Nissan 350z Touring 6mt
2000 4runner Limited
Tyler Williams
We have become educated beyond our intelligence. -Jerry Clower
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06-11-2010, 02:16 PM
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#7
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Name: mondtster
Title: Too Much Time
Status: Not Here
Join Date: Jan 2009
Location: k74
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Posts: 1,206
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Quote:
Originally Posted by Knuckledragger
put about 120 - 150lbs of shop air on each cylinder with a gauge and ball valve inline. air the cylinder up and how fast the air leaks off. if you have the intake and exhaust off, you can listen for air bypassing the valves. i always use about 800psi of nitrogen on big engines. if you have a nitrogen bottle around and can plumb it up, i would use it.
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The amount of pressure is subjective, IIRC the aviation industry takes their measurements at 80 psi. A lot of people use 100 psi because then whatever you read on a gauge would be the percentage.
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06-11-2010, 11:25 PM
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#8
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Name: joefarmer
Title: MR. Supreme Overlord
Status: Not Here
Join Date: Jul 2006
Location: ohio
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Posts: 6,137
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Quote:
Originally Posted by BgBlDodge
My engine on compression was 475-500 on all 6.
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If you'd do a leak down or compression test on my race engine you'd think the gauge was broken.
__________________
brandon'); DROP TABLE Users;--1948 Dodge 1.5t 12v RH swap | 99 F250 12v RE test rkt | 11 X5 'no soup' | 08 F250 CR RE swap | 05 2500 CR 68 standalone
firepunk.com
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06-12-2010, 04:15 AM
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#9
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Name: Knuckledragger
Title: Knuckledragger
Status: Not Here
Join Date: Jun 2009
Location: Mt. Vernon, IN
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Posts: 236
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point takin guys. i use a higher pressure to simulate a little bit of an actual cylinder pressure. in fireman450's case there is the possibilty of more than just a cylinder/ring failure. doing this i can see if the air is going past the valves, head gasket, or the rings. once the pressure equalizes i shut the valve and see how long it takes to drop a certain amount of pressure. it works great on big engines. it may not be accurate for small ones
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06-12-2010, 11:06 AM
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#10
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Name: mondtster
Title: Too Much Time
Status: Not Here
Join Date: Jan 2009
Location: k74
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Posts: 1,206
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Quote:
Originally Posted by Knuckledragger
point takin guys. i use a higher pressure to simulate a little bit of an actual cylinder pressure. in fireman450's case there is the possibilty of more than just a cylinder/ring failure. doing this i can see if the air is going past the valves, head gasket, or the rings. once the pressure equalizes i shut the valve and see how long it takes to drop a certain amount of pressure. it works great on big engines. it may not be accurate for small ones
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I wasn't trying to say you were doing it wrong, if that's what you're thinking, just that there are several ways to do the test.
As with a compression test, the leak down test results should be taken with a grain of salt. The results will vary somewhat depending on how the engine is assembled as was inferenced earlier. The last SBF nitrous motor I put together would have looked like it was completely worn out if someone who didn't know how it was built were to leak it down.
Both compression and leak down tests have their place and I use both on a regular basis. I usually start with a leak down test and proceed from there depending on what I find.
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06-12-2010, 11:16 AM
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#11
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Name: Fireman450
Title: Daring to be diffrent!!
Status: Not Here
Join Date: Nov 2007
Location: Edmonton , KY
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Posts: 1,606
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Thanks for the info guys.
Brandon, I hear ya on the compression, mine would do the same thing on my puller.
Im just tryn to figure out where the line is for a rebuild. If I tear it down, it will get a full treatment.
Cyl PSI
1 380
2 420
3 370
4 475
5 400
6 450
Ill do a leak down test and see for sure. I know that IMHO the compression test says its shot..lol and I think there is way to much varaition in psi between cyls.
Lynn
__________________
Lynn Chapman
Driver: 04.5 CR
Play Toy:1994 Dodge 12V, SMOKE SHOWIN! 2WD Pulling Team. vs. 3.0 in progress. Thanks to Northeast Diesel, MUMAU DIESEL , PullTech Chassis & Fab, Cooper High Performance, SKPP, Joe Gibbs Racing/Driven Racing Oils and all my friends and family!
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06-12-2010, 01:47 PM
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#12
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Name: joefarmer
Title: MR. Supreme Overlord
Status: Not Here
Join Date: Jul 2006
Location: ohio
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Posts: 6,137
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Sorry, my last post was less than helpful.
If I had to take a wild stab in the dark, 1,3,5 have light scoring on the cylinder walls. Tyler is correct with ~500psi static numbers.
__________________
brandon'); DROP TABLE Users;--1948 Dodge 1.5t 12v RH swap | 99 F250 12v RE test rkt | 11 X5 'no soup' | 08 F250 CR RE swap | 05 2500 CR 68 standalone
firepunk.com
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06-12-2010, 03:31 PM
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#13
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Name: NickTF
Title: Single turbo turd.
Status: Not Here
Join Date: Jun 2007
Location: Laurel, DE
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Posts: 5,887
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What fitting do you guys use in the injector bores when doing a leak down? I'm thinking setting my regulator in my air compressor to 100psi with the compressor air valve open, closing the compressor air valve, and then observing the pressure drop at the regulator gauge. Sound feasible?
__________________
97 12v sold. 2015 Power Wagon DD!
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