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Registered User
Join Date: Sep 2014
Posts: 19
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79 911SC Valve overlap issue
I am reassembling a 1979 911 930/03 top end. Nothing has changed in bottom end or heads/cams, except new valve guides & springs. Something is not working with setting valve timing. Standard intake overlap for my engine is 1.4-1.7 (1.55)mm. However, I can rotate crank over 360 deg before I achieve that value. I have been following the Dempsey rebuild manual religiously. Any ideas how I can fix problem, or what I might be doing wrong?
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10-28-2015, 08:10 AM
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I would rather be driving
Join Date: Apr 2000
Location: Austin, TX
Posts: 9,108
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Cam timing takes two complete revolutions (720 deg) of the crank. Cams turn 1/2 speed as crank.
crank angle /////// Cyl1 position /////// cyl4 position 0 /////// TDC (no overlap) /////// overlap at measured height 360 /////// overlap at measured height /////// TDC (no overlap) 720 /////// TDC (no overlap) /////// overlap at measured height sorry table I created does not work right. So position dial gauge on #1 with engine at TDC. zero gauge. roll engine 360 deg. Set overlap to spec (1.55mm). Roll engine 360 deg and make sure you are at zero again. Then repeat to other side. Hope this helps.
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Jamie - I can explain it to you. But I can not understand it for you. 71 911T SWT - Sun and Fun Mobile 72 911T project car. "Minne" - A tangy version of tangerine #projectminne classicautowerks.com - EFI conversion parts and suspension setups. IG Classicautowerks |
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10-28-2015, 11:36 AM
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Registered User
Join Date: Sep 2014
Posts: 19
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Indicator is at about 0.95mm after 360 rotation. How do I "set overlap to spec 1.55"? Do I remove pin at 360, advance crank until indicator reads 1.55 then re-position pin? Sorry to be slow, this is my first attempt at this.
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10-28-2015, 12:31 PM
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Registered
Join Date: Oct 2008
Location: Nash County, NC.
Posts: 8,508
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You advance the cam, not the crank
1 revolution from Z1 pull the pin and advance the cam to the design number Pin it, lock the nut on. Rotate 720 to check your pin setting. Bruce |
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10-28-2015, 01:13 PM
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Registered User
Join Date: Sep 2014
Posts: 19
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OK think I got it. I'll give it a whirl.... Does advancing timing on #1 & #4 intakes affect anything else in the process?
Thanks |
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10-28-2015, 01:24 PM
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Registered
Join Date: Oct 2008
Location: Nash County, NC.
Posts: 8,508
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If you get your design number on 1 and 4 intake, all will follow. Make sure you have the intake rocker you're measuring is properly adjusted.
Bruce |
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10-28-2015, 02:58 PM
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