Leak down test help
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Leak down test help
Hi guys. I have a 1985 Corvette. I also have AFR 195 Eliminator heads.
My timing chain broke and took out 3 valves.
Here were my leak down test results from before I pulled the heads off with the bent valves.
1. 20%
2. 13%
3. 95% intake
4. 13%
5. 95% exhaust
6. 15%
7. 95% exhaust
8. 20%
I took my heads to the machine shop and had a valve job done on both heads.
When I bolted the heads on, I took another leak down test. The engine is cold and I haven't ran it yet. I did wipe oil on the cylinder walls, and there is no oil in it right now.
About 3 of my cylinders were above 30% with a peak of 36%. The lowest cylinder I believe was 17%. I was just wondering if this is a normal result for a cold engine with new head gaskets and a fresh valve job? Is there a time it takes to seat in?
Thank you.
My timing chain broke and took out 3 valves.
Here were my leak down test results from before I pulled the heads off with the bent valves.
1. 20%
2. 13%
3. 95% intake
4. 13%
5. 95% exhaust
6. 15%
7. 95% exhaust
8. 20%
I took my heads to the machine shop and had a valve job done on both heads.
When I bolted the heads on, I took another leak down test. The engine is cold and I haven't ran it yet. I did wipe oil on the cylinder walls, and there is no oil in it right now.
About 3 of my cylinders were above 30% with a peak of 36%. The lowest cylinder I believe was 17%. I was just wondering if this is a normal result for a cold engine with new head gaskets and a fresh valve job? Is there a time it takes to seat in?
Thank you.
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
That's a lot of leakage, especially if you oiled the cylinder walls. The fresh heads should seal completely; the valves should be tight on their seats. Can you tell where the air is leaking? exhaust, throttle body, valve cover filler cap? The air is going somewhere.
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Through the valves. I sprayed some PB blaster into the intake port on the cylinder that has 36%. Put the leak down tester on it. Here's a video of what happened. http://youtu.be/KH7r0SwNCh0
Le Mans Master
Joined: Feb 2005
Posts: 6,485
Likes: 566
From: Clearwater Florida
...... Did you adjust the valves before the second leakdown ? If so , you may have done it wrong ... its easy to screw up using the spin the pushrod method and you wind up with valves off seats instead of just pre-loaded .........
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
No I didn't have the rocker arms on when I did this test.
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Race Director
Joined: Apr 2003
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From: moraga ca
They are all leaking. With 130lbs closing pressure, a closed valve is closed. My money is on a lously valve job. After a good valve job is done, alcohol can be poured on the top of the valve. There should be no leakage.
Last edited by 383vett; Sep 7, 2014 at 01:39 PM.
100%. That video tells the story....assuming clean assembly.
Thread Starter
Melting Slicks
Joined: Jun 2013
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Likes: 39
I poured lacquer thinner in the ports of the valves and it didn't leak through, but it still leaks on the engine...
Race Director
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From: moraga ca
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
I made a little break through. I poured a little bit of oil into cylinder 6 which had 36% leak down. That's also the affected cylinder in the video or the valve with the PB blaster bubbling. Now when I did the test again, it now has 18% leak down. So is the amount of air escaping get out of the valves acceptable for a cold leak down test if the oil dropped it significantly?
Thanks guys
Thanks guys
Thread Starter
Melting Slicks
Joined: Jun 2013
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Likes: 39
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Called the machinist, told me to run the motor for 10 minutes and check again. Said the valves have to seat... I'm doing a compression test on all cylinders now. Getting pretty decent results and the only cylinder i put oil in was number 6. Also there's no oil in the motor during this test. I'll post the results in a few minutes when I finish.
Last edited by DanielRicany; Sep 8, 2014 at 05:01 PM.