Leak down test
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Leak down test
Well after reading http://forums.corvetteforum.com/show....php?t=1075452 I rechecked my readings I posted earlier with one big difference I thought "dynamic" compression meant with engine running, you know dynamic versus static OOOOPSSS. In the Navy we call that a "GCE" (great conceptual error) anyway with coil wire off I cranked it over 5 times each cylinder and heres what I got
DRY / WITH 2 PUMPS OF 80 WEIGHT
#1 155 160
#2 149 160
#3 150 157
#4 147 160
#5 150 162
#6 147 165
#7 155 160
#8 145 160
I'm happy!
Okay next step is going to Kragen Auto picking up the leak down tester and give that a try. I'm happy so far and maybe all I'm looking at is new valve seals versus a total rebuild.
DRY / WITH 2 PUMPS OF 80 WEIGHT
#1 155 160
#2 149 160
#3 150 157
#4 147 160
#5 150 162
#6 147 165
#7 155 160
#8 145 160
I'm happy!
Okay next step is going to Kragen Auto picking up the leak down tester and give that a try. I'm happy so far and maybe all I'm looking at is new valve seals versus a total rebuild.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
I thought that was a compression test. I thought with leak down you used shop air, put a set pressure in the cylinder and then measured how much was lost or leaked out giveing a leak down reading?
Drifting
Joined: Mar 2003
Posts: 1,608
Likes: 3
From: Canberra AUSTRALIA
St. Jude Donor '05-'06
Dave,
Numbers look OK. Your wet numbers are close to mine dry but mine is a fresh rebuild. You do have higher compression though so I would figure a rebuild of your engine would yield 170-180PSI.
The 15PSI difference between dry/wet concerns me. I need an engine guru to jump in here. 15PSI sounds like enough pressure to push oil around to me hence it may well be blowpast the rings as suspected. Anyone have thoughts on this?
Cheers,
Pete
Numbers look OK. Your wet numbers are close to mine dry but mine is a fresh rebuild. You do have higher compression though so I would figure a rebuild of your engine would yield 170-180PSI.
The 15PSI difference between dry/wet concerns me. I need an engine guru to jump in here. 15PSI sounds like enough pressure to push oil around to me hence it may well be blowpast the rings as suspected. Anyone have thoughts on this?
Cheers,
Pete
Senior Member since 1492
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by norvalwilhelm
I thought that was a compression test. I thought with leak down you used shop air, put a set pressure in the cylinder and then measured how much was lost or leaked out giveing a leak down reading?
Senior Member since 1492
Joined: Aug 2000
Posts: 87,930
Likes: 156
From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by norvalwilhelm
I thought that was a compression test. I thought with leak down you used shop air, put a set pressure in the cylinder and then measured how much was lost or leaked out giveing a leak down reading?
.....
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by Cali,68,L-79
#1 155 160
#2 149 160
#3 150 157
#4 147 160
#5 150 162
#6 147 165
#7 155 160
#8 145 160
I'm happy!
so what that means to me is that you have some rings that are worn and valves are fine... is that what you are thinking?
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
No I'm hoping it means the rings are fine. Well no one has a leak down tester available to rent out. Hopefully next week the 2 units are back to the store from whomever is borrowing them and I can do the leakdown test. that will be the true indication.
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Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Originally Posted by stingry
Dave,
Numbers look OK. Your wet numbers are close to mine dry but mine is a fresh rebuild. You do have higher compression though so I would figure a rebuild of your engine would yield 170-180PSI.
The 15PSI difference between dry/wet concerns me. I need an engine guru to jump in here. 15PSI sounds like enough pressure to push oil around to me hence it may well be blowpast the rings as suspected. Anyone have thoughts on this?
Cheers,
Pete
Numbers look OK. Your wet numbers are close to mine dry but mine is a fresh rebuild. You do have higher compression though so I would figure a rebuild of your engine would yield 170-180PSI.
The 15PSI difference between dry/wet concerns me. I need an engine guru to jump in here. 15PSI sounds like enough pressure to push oil around to me hence it may well be blowpast the rings as suspected. Anyone have thoughts on this?
Cheers,
Pete
Drifting
Joined: Mar 2003
Posts: 1,608
Likes: 3
From: Canberra AUSTRALIA
St. Jude Donor '05-'06
Cali,
With unknown enginen components its true the compression could be different. 160PSI is still healthy inmho.
My concern is that the difference between wet/dry is leaning towards your rings not sealing. I hope that your leakdown test proves otherwise.
Cheers,
Pete
With unknown enginen components its true the compression could be different. 160PSI is still healthy inmho.
My concern is that the difference between wet/dry is leaning towards your rings not sealing. I hope that your leakdown test proves otherwise.
Cheers,
Pete
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by Cali,68,L-79
No I'm hoping it means the rings are fine. Well no one has a leak down tester available to rent out. Hopefully next week the 2 units are back to the store from whomever is borrowing them and I can do the leakdown test. that will be the true indication.
i thought the theory went that if the oil increases compression it is because it creates a small film on the cylinder walls indicating that the rings were not as tight or sealing as well as before....if the oil does nothing to incease compression then the problem is the valves
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Well my theory, and it's just a theory, when you crank over the engine five times the oil pump will splash up to the botttom of the rings and it will drip down. Succeding turning over of the engine for the rest of the cylinders will continue to load the block with oil from the pan so there still should be some oil at the rings making any increase in oil say the 80 weight I shot in the spark plug hole insignificant. Maybe I'm just hopeful. Who knows. 
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Originally Posted by LiveandLetDrive
But it did make a difference?
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by Cali,68,L-79
Well my theory, and it's just a theory, when you crank over the engine five times the oil pump will splash up to the botttom of the rings and it will drip down. Succeding turning over of the engine for the rest of the cylinders will continue to load the block with oil from the pan so there still should be some oil at the rings making any increase in oil say the 80 weight I shot in the spark plug hole insignificant. Maybe I'm just hopeful. Who knows.
i don't think so, but i hope i'm wrong for your sake...the bottom ring is and oil scaper ring its mission is to stop the oil from getting by it....the top rings are the compression rings thats why the oil you shot in there made a difference.