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Old 03-23-2009, 08:40 AM   #1
stitchbad
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Default Leaking valves

Ok so I just got my motor back from the machine shop for the fourth time and found that first they shaved the tops of some of my buckets to get the right spacing on the intake and exhaust cams (don't know I'm screwed now). Once I got the timing belt on and set I did a leak down test, all of my valves are leaking, you hear the air passing. The leaks are small I losing only 4 to 6% but still the valves shouldn't pass at all right. Any help would be great.

Details:
04 STI EJ257 motor
Brand new EJ 257 short block
ARP head studs
Subaru head askets
Heads where decked
Valve grinder done
New valve guides and seals
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Last edited by stitchbad; 03-26-2009 at 10:05 AM.
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Old 03-24-2009, 03:53 PM   #2
madmax718
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I think shaving the buckets would only increase the tension on the valves, and has nothing to do with the air that is passing. If your getting air passing, that means that the valves are partially open (forwhatever reason).

If they valve grinded properly, they would have had a good fit- its common to grind the valve tips to make it fit better however.
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Old 03-24-2009, 04:26 PM   #3
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Have the valves been lapped-in yet? You listed everything done, but I don't see lapping on the list. If you fill the chambers with kerosene and let them sit (flat on a bench) can you see the leakage out the ports? If the clearances are right and the valves are not bent, and the valve job was done properly, lapping would be the final step to a good seal.

Jay
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Old 03-24-2009, 05:04 PM   #4
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yeah gotta lap them valves, easy as cake.
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Old 03-24-2009, 06:14 PM   #5
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Make sure your piston is at TDC of the compression stroke when you are doing the leak down test or it will show leaks. I'm sure you already knew that though.
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Old 03-24-2009, 08:05 PM   #6
stitchbad
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I have it at TDC and I checked there is clearance between the cam and the valve, it's good. As for lapping I'm not sure but would hope they did, it seem that when I bolt the heads on to the block there are leaks in the valves. The machine shop say that there are no leaks when they bench tested them but when there on the block they leak air.
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Old 03-25-2009, 02:13 AM   #7
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are you sure you're hearing air leak past the valves? you WILL hear it leak past the rings.
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Old 03-25-2009, 08:42 AM   #8
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I was going to ask where the air was leaking to, but assumed it was from the exhaust pipe or intake manifold and not the breathers. It would be good to know in trying to diagnose this.

Jay
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Old 03-25-2009, 08:46 AM   #9
stitchbad
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it's leaking from the intake and exhaust ports, right now the motor is not in the car.
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Old 03-25-2009, 08:47 AM   #10
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Quote:
Originally Posted by Maxwell Power View Post
are you sure you're hearing air leak past the valves? you WILL hear it leak past the rings.
yup if you look in the port you can see bubbles
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Old 03-25-2009, 12:03 PM   #11
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Your leaking past the intake and exaust ports? Even if the cams arent touching the buckets, it does not mean that the valves are fully seated.

It is possible they mixed up the valves when you had them ground- they are almost port specific after a while, and when taking it apart, you need to know which valve goes where. If they simply took them all out, had it on a bench, , and put it back together after new stems, it is possible they mixed it up.

Also to do a test for leakage on a bench, they would need to do a full plate to seal the dome.
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Old 03-25-2009, 01:22 PM   #12
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Quote:
Originally Posted by stitchbad View Post
yup if you look in the port you can see bubbles
I speak from experience when I tell you that they leak small amounts from the factory. The factory doesn't lap the valves and they leak a bit until they are run.

We lap our valves all the time, but it isn't always necessary.

However, if you have the engine out of the car, feel free to pull it apart and lap everything.
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Old 03-26-2009, 12:11 AM   #13
stitchbad
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Quote:
Originally Posted by Maxwell Power View Post
I speak from experience when I tell you that they leak small amounts from the factory. The factory doesn't lap the valves and they leak a bit until they are run.

We lap our valves all the time, but it isn't always necessary.

However, if you have the engine out of the car, feel free to pull it apart and lap everything.

What's a small amount, I can hear the air passing and the last time it sounded like that it was a bent valve. I will ask if they lapped the valves tomorrow.
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Old 03-27-2009, 01:27 PM   #14
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Quote:
Originally Posted by Storm View Post
Have the valves been lapped-in yet? You listed everything done, but I don't see lapping on the list. If you fill the chambers with kerosene and let them sit (flat on a bench) can you see the leakage out the ports? If the clearances are right and the valves are not bent, and the valve job was done properly, lapping would be the final step to a good seal.

Jay
does this have to be done with kerosene?is it something where the kerosene makes them seal? or can it be done with a similar fluid?
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Old 03-27-2009, 04:43 PM   #15
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Well, Kerosene isn't as flammable as gas, but you can also try an extremely light weight oil. I wouldn't want to use water unless I were going to disassemble everything right after the test. The thicker the fluid, the longer it'll take to get past small leaks. Air is pretty thin, so you'd want as thin a liquid as you can find....within reason.

You can spray WD40 into the chambers until they fill up enough to allow some drainage through any leaks.

Jay
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Old 03-27-2009, 04:55 PM   #16
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If any of the valves are open it will and should blow air through the exhaust and if turned the intake manifold....


Quote:
Originally Posted by stitchbad View Post
it's leaking from the intake and exhaust ports, right now the motor is not in the car.
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Old 03-27-2009, 04:58 PM   #17
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Quote:
Originally Posted by Storm View Post
Well, Kerosene isn't as flammable as gas, but you can also try an extremely light weight oil. I wouldn't want to use water unless I were going to disassemble everything right after the test. The thicker the fluid, the longer it'll take to get past small leaks. Air is pretty thin, so you'd want as thin a liquid as you can find....within reason.

You can spray WD40 into the chambers until they fill up enough to allow some drainage through any leaks.

Jay
i used windshield washer fluid,it was all i had close by it worked fine,no leaks
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Old 03-27-2009, 05:17 PM   #18
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So you're passing air somewhere else.....like the rings.

Jay
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Old 03-27-2009, 08:34 PM   #19
stitchbad
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yes there's air passing the rings. I took it to the shop and they're going to do it again but they don't lap valves so now I have to get the stuff to do it or find someone who can.
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Old 03-28-2009, 12:49 AM   #20
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You can do it yourself. It's time consuming, but still possible and easy.

Valve lapping compound is available at most any autoparts store (gritty paste). Use some paste on the valve sealing surface and turn the stems (after removing the springs and stuff) while applying light pressure. Small suction cup tools make it a litle easier on your fingers and thumbs, but once done, you'll have smooth mating surfaces that fit nicely.

Jay
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Old 03-28-2009, 03:09 PM   #21
stitchbad
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Do I need to lap my valves or are they going to seat on there own when I run the motor?
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Old 03-29-2009, 12:17 PM   #22
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You should lap them in if they leak. If they don't leak, you don't need to....but it helps.
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