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Join Date: Oct 2001
Location: San Carlos, CA US
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Valve job, and then not running right

I need some hints.

I did a valve job on the 80SC. Heads work was done by German Precision in Sunnvale, good job!

5 of the rocker arms were out out specs (0.005 to 0.008 larger than the shafts) so I replaced them with some better ones I had left over from my Carrera days. They were all tighter than the SC ones. Also changed the chains and the sprockets.

The engine already had the oil fed tensioner updates 3 years ago, so I just reused those.

Reinstalled everything, ran the engine for 30 minutes, and it is not running right:

1. loud valve noises
2. some popping at idle
3. low on power

What I checked:

a. dynamic timing of the engine with a timing light, and it is firing right at Z1 mark, when I increase the engine speed, I can see the timing becoming more advanced.

b. Static timing checked and rechecked, left bank right at 0.1mm, right bank at 0.08mm (slightly out of spec, but this cannot be that disastrous)

c. valve clearance right on a 0.1mm.

OK, engine experts, give me some directions. I have tried everything I know.

* Are SC rocker arms same as Carrera rocker arms?
* is 0.08mm vs 0.09mm valve timing that big of a deal to cause that much valve noise

thanks,

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Old 11-03-2007, 04:26 PM
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Not sure about SC, but my Carrera I think I set the valves to .004 clearance.
I think you wrote you set yours to .1 - that may be a bit of the noise.
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Emery

1988 930 coupe - Silver Metallic
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Old 11-03-2007, 04:40 PM
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SC should be .004 as well. I believe all models from 78-89 are .004. I use the feeler guage to double check, but I have found I get better results just by listening to the sound the rockers make when I wiggle them back and forth.
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John A.
1979 Porsche 930: 3.4L, SC cams, Twin plug, Leask WUR, Custom SSI turbo exhaust, Tial WG, K27HFS, and we can't forget the Zork (short lived depending on my homeowners assoc.)
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Old 11-03-2007, 05:52 PM
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0.1mm is 0.004" (4 thousandths of an inch). I used the feeler gauge, the only the one I have for the Porsche.
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Old 11-03-2007, 05:57 PM
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Your terms are not clear to me but here are some guesses. When you say dynamic timing with different numbers are you talking about your cam timing? The numbers you say of .1mm or .08mm are not correct for cam timing on an SC (or any other car for that matter).

Your valve clearance should be set to .004 inches or .1mm. Your cam timing should be set to 1.4-1.7mm at TDC on the overlap. Your idle ignition timing should be around 5 degrees BTDC I think.

-Andy
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Old 11-03-2007, 07:02 PM
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So, the question is was your cam timing reset correctly after the head job? The camshafts had to be removed, so the cam timing was lost; Who reset it and are you sure about that setting?

Aurel
Old 11-03-2007, 07:09 PM
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Thank you, I found the problem from your comments.

I did the valve timing to the wrong value. Your comment is 1.4-1.7mm, while Wayne's engine rebuild book says 1mm. Before I go through all the trouble again, which value is right?

Secondly, I also set the ignition timing to the wrong value, Z1 instead of 5 degrees before tdc.

The world is all right again if some one can tell me what the correct Valve timing set value is, 1mm or 1.4 - 1.7mm.
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Old 11-03-2007, 09:20 PM
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Your answer may be there:

'80 3.0 cam timing

Aurel
Old 11-04-2007, 02:18 AM
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Thank you all, it was success after I reset the valve timing to 1.55mm. Fires right up and purrs

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Old 11-04-2007, 06:14 PM
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