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03-23-2009, 07:40 AM | #1 |
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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 09:05 AM. |
03-24-2009, 02:53 PM | #2 |
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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. |
03-24-2009, 03:26 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 |
03-24-2009, 04:04 PM | #4 |
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yeah gotta lap them valves, easy as cake.
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03-24-2009, 05:14 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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03-24-2009, 07:05 PM | #6 |
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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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03-25-2009, 01:13 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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03-25-2009, 07:42 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 |
03-25-2009, 07:46 AM | #9 |
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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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03-25-2009, 07:47 AM | #10 |
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03-25-2009, 11:03 AM | #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. |
03-25-2009, 12:22 PM | #12 |
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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. |
03-25-2009, 11:11 PM | #13 | |
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Quote:
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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03-27-2009, 12:27 PM | #14 | |
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03-27-2009, 03:43 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 |
03-27-2009, 03:55 PM | #16 |
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03-27-2009, 03:58 PM | #17 | |
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03-27-2009, 04:17 PM | #18 |
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So you're passing air somewhere else.....like the rings.
Jay |
03-27-2009, 07:34 PM | #19 |
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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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03-27-2009, 11:49 PM | #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 |
03-28-2009, 02:09 PM | #21 |
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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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03-29-2009, 11:17 AM | #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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