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Old 10-11-2007, 08:59 PM   #1
TyranosaurusWRX
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Default Once the fence...

I put a set of newly refreshened heads on my shortblock. I tightened down the heads and performed a leakdown test. Three of the cylinders leaked down between 3-5%, cyl 4 leaked down at 8%. I traced the leak to be on the exhaust side, both valves. I could feel a bit of air coming out of the port, confirmed it by spraying wd40 in there and it misted out. I guess what I need to know is, is 8% acceptable? I wonder if the valves will "settle" a little tighter once everything is broke in? On one hand, I guess I could take it apart while it's still out, on the other, I wonder if I should bother......
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Last edited by TyranosaurusWRX; 10-11-2007 at 09:00 PM. Reason: Lets try "on the fence" geez I need to proof read
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Old 10-11-2007, 09:37 PM   #2
flycaster
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Check the cam belt for proper install first, but the bottom line is they shouldn't leak at all. If you're positive it is leaking at the valve, and the cam timing is good, send 'em back.

[edit] - That's a real nonsequitor thread title. Inside joke, or am I just dumb?

Last edited by flycaster; 10-11-2007 at 09:45 PM.
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Old 10-11-2007, 10:13 PM   #3
TyranosaurusWRX
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Actually, in order to keep all the valves closed, I just left the timing belt off. That way I didn't have to worry about setting the compression stroke.

As far as the title, did you see my edit note? I meant on the fence - as in not sure which way I'm going to go.
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Old 10-12-2007, 01:01 AM   #4
flycaster
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Ahh, no I didn't see that. Yeah, if you just had a valve job done, they shouldn't pass any air - something is definitely wrong.
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Old 10-15-2007, 07:24 PM   #5
shvrdavid
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Quote:
Originally Posted by flycaster View Post
Ahh, no I didn't see that. Yeah, if you just had a valve job done, they shouldn't pass any air - something is definitely wrong.
That would depend on how the seats were cut...

I use carbide cutters on most of the hardened seats I do, and the valves will leak a little bit...

When the seats are done this way, they seal up after initial startup...
Not sure what percent they would leak though...

This explains what I mean... Click Here

If the valves were lapped into the seat, they will still leak a little bit as well...
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Old 10-15-2007, 08:28 PM   #6
flycaster
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I would think they'd be lapped a smidge even with a 3 angle cut, and a lot of shops will vacuum test at the end - I dunno either how that translates in LD %'s, but an 8% loss just doesn't seem right. Maybe I'm off target here?
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Old 10-15-2007, 09:43 PM   #7
TyranosaurusWRX
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Seems like you are both on target- thanks for your input(s). I tore the head down last weekend, turns out two of the valves (the leaky ones) were bent ever so slightly. I had a couple back ups so I put them in there an lapped them. Now they are sealing as well as the others. You can hear a bit of air flow in all of them, but nothing like the bent ones were showing.
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Old 10-15-2007, 11:42 PM   #8
flycaster
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Good deal. I know the theory is they pound in for a 100% seal after a very short time, but 8% seemed really high - especially the visible "mist" part.

There was a thread on another board where a guy could actually blow soap bubbles through a couple of valves right after a $1,500 head rebuild - turned out the factory replacement guides were incorrectly drilled and the hole was not concentric. The shop didn't pick up on this and needless to say the poor guy was upset, but in the shops defence it's probably not something that happens every day either. They fixed it with no whining.
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