compression test looks bad, HELP

68GEETEE

5 Year Member

Nov 21, 2003

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Texas, USA

Jan 18, 2004

#1

• Jan 18, 2004

• #1

MY '68 302 4bbl is using a quart of oil every 300-500 miles. It doesnt seem to smoke, except for when first started up.

I just did a dry/wet compression test today and here are the results.

dry test lowest cylinder reading was 162
dry test highest cylinder reading was 173

wet test every cylinder reading jumped from 5 to 15 points over dry reading.

Does this mean my rings are not sealing???

Where do I go from here?


Dave


p.s. engine block was bored .020, but i dont know how long ago it was done.

 

dodgestang

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#2

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• #2

What was the variance from highest reading to lowest reading in the dry test?

 

crushnut

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#3

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Looks like there was a 11 psi variance between his highest dry test and lowest dry test.

 

crushnut

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#4

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Looks like there was a 11 psi variance between his highest dry test and lowest dry test. But that is just from the information that he gave us.

 

dodgestang

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#5

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crushnut said:

Looks like there was a 11 psi variance between his highest dry test and lowest dry test. But that is just from the information that he gave us.

Click to expand...

LOL - I read that darn thing three times and thought it said dry for the first like and wet for the second line....I must be getting old.

 

S

StangPowerSoon

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#6

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Alright Dave, heres the low down. Your gonna want to run a pressure lost test, using compressed air you keep air in the cylinder and you allow for the guage to measure how much air its losing. However when you run this test, listen for hissing or what sounds like air coming from your engine. Also Open your oil fill cap and feel for air. Also do the same with the tail pipe. If you have air coming from your cap or your tail pipe. You have a faulted value either Exhaust for the pipe or Intake for the oil cap. But however if you hear air in your crank case you have faulty rings and most likely they will need to be replaced. Also when you run this test. Make sure your engine is warm not hot and off!, and also remove you radiator cap so the pressure doesnt crack your radiator.

You can find a pressure leakage Test kit at local car shops, at least here in Oregon. Hope this helps.
Tim

 

68GEETEE

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Nov 21, 2003

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Jan 18, 2004

#7

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• #7

Tim, thanks for your reply. I have heard of that test referred to as a 'leak down' test. I didnt do it because I didnt have the correct gauges. However, given the results of my dry/wet test, isnt it conclusive from what I described that the rings are the problem. I mean, if it was valves or such, why would the wet test spike the compression??

 

S

StangPowerSoon

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#8

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Your compression will always be higher with a wet compression test Dave, that applies for all engines because oil helps make one of the seals between the cylinder wall and the rings. The thing you have to worry about is a larger then 10% difference from dry to wet. If you have 100 psi per cylinder on dry it shouldnt be more then 110 on a wet. Also you can safely have up to 10 to...15% not sure on this one variatance between cylinders. ((I would have to check a refrence on that.) Hope this helps again.

 

68GEETEE

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Nov 21, 2003

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Jan 18, 2004

#9

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the cylinder readings were as follows:

#1 dry 165 wet 170
#2 dry 170 wet 175
#3 dry 169 wet 174
#4 dry 169 wet 180
#5 dry 167 wet 174
#6 dry 162 wet 170
#7 dry 165 wet 180
#8 dry 173 wet 180

In looking on the net, opinion seems to be that the wet should only be 1 to 3 points higher than dry. If its more, then you have a ring problem. Can anyone verify or dispell this finding?

 

crushnut

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#10

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If im not mistaken a wet test will always have an increase, over a dry test.

Edit- Oops, Tim already said that

 

S

StangPowerSoon

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#11

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If it was your rings...you would have blue smoke coming from your tail pipe because oil would be in your combustion chamber. I dont know who your talking too but....I cant help you much more ^^. Good Luck on your vehicle

 

68GEETEE

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Nov 21, 2003

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Jan 18, 2004

#12

• Jan 18, 2004

• #12

Is there another factor besides worn rings that could cause a quart of oil to disappear within 300 miles? No leaks on my garage floor, and no tailpipe smoke when she is warmed up.

 

68GEETEE

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Nov 21, 2003

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Jan 18, 2004

#13

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• #13

This is the site that I took info from regarding compression findings:

http://www.cobra-replica.co.uk/html/cobra_52.shtml

 

crushnut

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#14

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I wouldn't be too worried about those numbers if they are indeed accurate, although thats just me .
(but hey, what do i know)

 

S

StangPowerSoon

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#15

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Yes..A worn value seat allowing oil onto the value would burn off and come out as undectectable smoke beneath your hood. Also did you know 2 drops of oil every 50feet, every 50 feet, while the engine is running will cause a quart of oil to burn up in 500 miles? =P. Forgot to mention that your Exhaust value runs around 1500 degrees on a general day.

Edit: also on your site it says tests should be within 10% exactly what I said if I do recall =P. But hey thats just me =)

 

68GEETEE

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Nov 21, 2003

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Jan 18, 2004

#16

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Tim,

Valves can do that? I wasnt aware of it. I guess the leak down test is what will tell on that , yes?

 

S

StangPowerSoon

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#17

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Yeah, the leak down test as you accurately stated the name =P. Will tell you what you need to know. I would just hate to see you either have to struggle with tearing your whole engine down and rehoning the cylinders and then installing new rings on trued Pistons when all you had was a faulty value. Its always good to run more then 1 type of test to verify your findings. Remember if you hear air in your crankcase, a.k.a your oil pan you know you do actually have those worn pistons. I hope this helped you.
Tim

EDIT: also if you cant get a cheap kit, see how much it runs to have a shop do one for ya. =P

 

G

GaPonyFarm

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#18

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If it just smokes when you start the car, it could be as simple as valve stem seals (a really simple repair). Does the car begin to smoke at very high rpms also, but not under normal conditions? This is also a sign of valve stem seals. The recommendation for a leak down test was a good one. The cylinder pressure test results looks pretty good, I'd start looking beyond the rings, to the heads.

 

S

StangPowerSoon

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Jan 19, 2004

#19

• Jan 19, 2004

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Good call Pony, I completely forgot about value stem seals. =P
Now I feel all dumb =P.

 

C.Harris

Da Boss

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#20

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Valve stem seal or worn valve guides may be the culprit here. If you do pull the heads for freshening you may want to consider bronze guides and a nice 3 angle valve job with the rebuid.