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Join Date: Mar 2007
Location: NYC berbs
Posts: 345
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Need Cam Timing Advice 79SC
I was trying to do the timing on the left cam last night.
I just had my cams re-ground to 964 profile (overlap is 1.26mm) and I have replaced both chains. I clamped my chain tensioner gear so it is very tight. I did everything (a number of times) by the book up to this point. When I got to 1.26mm and the set the Crank at the Z mark, I inserted the pin in the cam sprocket, when I let go of the cam it slipped back to .9mm on the gage, if I went to 1.3mm and inserted the pin (it went to a different hole on the sprocket) the cam didn't slip back and stayed there. So I went back to 1.26mm at the z mark on the crank, inserted the pin in the cam sprocket, held the cam in position so it didn't slip back and torqued down the cam nut. Is this correct? Or is something worn or did I do something wrong. Other than this, cam timing is just taking your time and making sure all measurements (like the being at the precise Z mark every time) are correct and accurate. Please advise |
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06-20-2009, 06:19 AM
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Join Date: May 2003
Posts: 3,346
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Yes, the pin has "slop" in it. Some have more slop than others. The pin doesn't take any load (as far as I know) once the bolt is torqued down.
-Andy
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72 Carrera RS replica, Spec 911 racer |
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06-20-2009, 11:41 AM
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Join Date: Mar 2007
Location: NYC berbs
Posts: 345
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Thank you, this is my first rebuild and a mess up is just too expensive so I triple check everything!
dog |
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06-20-2009, 03:38 PM
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Join Date: Oct 2008
Location: Nash County, NC.
Posts: 8,512
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After you pin the gears, you have to load the cam pressure against the pin. The difference between one hole and the next is about .15mm after you load the cam. If you cant get the setting, release everything and turn the gear one chain cog and try again
Look up the cam timing, there is usually a window and I always try to go high in the window to allow for heat and the chain length change with the heat. Bruce |
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06-20-2009, 03:43 PM
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Join Date: May 2003
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Why would you have to load the cam pressure against the pin? Which way would you load it? As far as I can tell the cam has shock loads in both directions depending on the stroke the engine is on or the way the clutch is popped.
-Andy
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72 Carrera RS replica, Spec 911 racer |
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06-20-2009, 05:00 PM
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Join Date: Oct 2008
Location: Nash County, NC.
Posts: 8,512
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Load the pin against the direction of cam movement (clockwise) because you dont want slack in the system as you read the dial guage. With the pin placed you still have dial movement so you press against the cam direction to get the final reading.
Bruce |
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06-21-2009, 06:07 PM
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