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Registered
Join Date: Jul 2007
Posts: 7
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Could Bad valve adjustment show up in leak down?
Picked up another 964 '90 with 110k miles.
If the valves were adjusted improperly - too tight on lash - would this show up as in a leak down? Engine sounds OK when running and power feels OK.  Definitely have leaks and trying to decide when to do the rebuild (will be my second 3.6 rebuild). |
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05-30-2008, 10:26 AM
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Moderator
Join Date: Dec 2001
Posts: 9,569
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Well certainly-- if some DPO has run the adjuster screws down so there is not only no clearance but the valve is held open when the rocker is on the base circle-- but somebody would have to affirmatively not know what the heck they were doing.
That said, valve adjustment is easy enough to verify. What are the leakdown numbers? Where from?
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'66 911 #304065 Irischgruen ‘96 993 Carrera 2 Polarsilber '81 R65 Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13) Ex-'88 Carrera (Sold 3/29/02) Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04) Ex-'89 944 Turbo S (Sold 8/21/20) |
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05-30-2008, 10:41 AM
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Max Sluiter
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If the valves are too tight, they may not be closed all the way and the compression test numbers and leak down will be bad.
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance |
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05-30-2008, 10:42 AM
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abit off center
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Even if they are closing but very close could have caused crap in the seat area and not let them seal, listen to where the air is venting.
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______________________ Craig G2Performance Twinplug, head work, case savers, rockers arms, etc. |
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05-30-2008, 10:56 AM
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Registered
Join Date: Jul 2007
Posts: 7
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Leak down was close to 20% all the way around. I can visualize the valves too tight and not seating as being part of the cause. I guess my real question is - if the valves were that far off in adjustment would the engine appear to run OK or would there be other noticable symptoms of a problem.
I've never heard a 3.6 run this quiet. |
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05-30-2008, 11:00 AM
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Moderator
Join Date: Dec 2001
Posts: 9,569
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Quiet? As in no valvetrain clatter? Easy enough to check.
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'66 911 #304065 Irischgruen ‘96 993 Carrera 2 Polarsilber '81 R65 Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13) Ex-'88 Carrera (Sold 3/29/02) Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04) Ex-'89 944 Turbo S (Sold 8/21/20) |
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05-30-2008, 12:39 PM
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Registered
Join Date: Jun 2004
Location: Rio Rancho, New Mexico
Posts: 1,325
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A leak down test is used to determine WHERE the low compression is coming from.
A 20% leakdown is part of the test. WHERE it is leaking is the other part. A simple compression test will give you a clue about engine health. If the valves are in fact too tight, a leakdown test will show intake, exhaust or both.
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DOUG '76 911S 2.7, webers, solex cams, JE pistons, '74 exhaust, 23 & 28 torsion bars, 930 calipers & rotors, Hoosiers on 8's & 9's. '85 911 Carrera, stock, just painted, Orient Red |
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05-30-2008, 02:45 PM
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1971 Porsche 911S
1969 and 1986 Porsche Targa and Coupe 1720cc and 3
