crank position/cam timing
12-02-2003, 11:59 PM
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crank position/cam timing
Hello All,
I am wondering if anyone has experienced what I have. I have a Tip (8-92 build, 93 m.y.) and there are NO TDC marks anywhere for the crank. So in doing my first timing belt 4 years ago, I just lined up the cam mark, didn't move anything and all is well. This time, I wanted to make sure that the crank is at TDC, per the factory repair manual instructions. After much searching, I found an extension tube and rod at Baum tools to allow the use of my dial indicator. What I found is very interesting.
1. Drawings in the 968 Porsche workshop manual show the dist rotor straight up with the cam timing mark about 40 degrees ATDC. On my car the rotor is about 40 degrees BTDC and the cam timing mark is straight up. No big deal, Porsche probably used old drawings.
2. Put on dial indicator and found crank was about 40 degrees ATDC, so I counter rotated the engine to put the crank at TDC, per the factory instructions. Put on timing belt, rotated engine and sure enough interferance. I suspected this as the engine would not run or very poorly at best with a crank this far out.
3. So I put crank back, but had to eyeball it to put the keyway straight up (position that I found it). Everything is OK now.
4. Nowhere in the manual does it ever say anything about #1 piston being ATDC. It always says at TDC. There is nothing about a mm drop of #1 or even a degree of ATDC for #1.
What gives? Are tips set up differently? Am I missing an update to my workshop manual showing a change?
The "Checking and adjusting the camshaft setting" in the manual is somewhat confusing. It only mentions a .39 +/- .03mm depression of the intake valve. Has any one followed these instructions before and got good results? Does the engine end up with the crank ATDC?
Everything is OK, but this is very un-German and very un-Porsche like to have the manual so far off the actual engine. Besides, I had to eyeball the crank setting, which is disturbing. I would rather have had a mm drop or degree setting, but this specification is nowhere to be found.
Thank you for any insight and I appologize of the rambling.
Mitch
I am wondering if anyone has experienced what I have. I have a Tip (8-92 build, 93 m.y.) and there are NO TDC marks anywhere for the crank. So in doing my first timing belt 4 years ago, I just lined up the cam mark, didn't move anything and all is well. This time, I wanted to make sure that the crank is at TDC, per the factory repair manual instructions. After much searching, I found an extension tube and rod at Baum tools to allow the use of my dial indicator. What I found is very interesting.
1. Drawings in the 968 Porsche workshop manual show the dist rotor straight up with the cam timing mark about 40 degrees ATDC. On my car the rotor is about 40 degrees BTDC and the cam timing mark is straight up. No big deal, Porsche probably used old drawings.
2. Put on dial indicator and found crank was about 40 degrees ATDC, so I counter rotated the engine to put the crank at TDC, per the factory instructions. Put on timing belt, rotated engine and sure enough interferance. I suspected this as the engine would not run or very poorly at best with a crank this far out.
3. So I put crank back, but had to eyeball it to put the keyway straight up (position that I found it). Everything is OK now.
4. Nowhere in the manual does it ever say anything about #1 piston being ATDC. It always says at TDC. There is nothing about a mm drop of #1 or even a degree of ATDC for #1.
What gives? Are tips set up differently? Am I missing an update to my workshop manual showing a change?
The "Checking and adjusting the camshaft setting" in the manual is somewhat confusing. It only mentions a .39 +/- .03mm depression of the intake valve. Has any one followed these instructions before and got good results? Does the engine end up with the crank ATDC?
Everything is OK, but this is very un-German and very un-Porsche like to have the manual so far off the actual engine. Besides, I had to eyeball the crank setting, which is disturbing. I would rather have had a mm drop or degree setting, but this specification is nowhere to be found.
Thank you for any insight and I appologize of the rambling.
Mitch
12-03-2003, 04:31 AM
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The 968 engine is the same no matter which 968 they came with. Exept the Turbo S and RS ofcourse.
40 degrees is about the tilt of the engine when mounted in the car. I hope you did not think the referance point is gravity (straight up or down).
The 968 workshop manual matches our two 968 engines perfectly. Did you remember that the engine is not sitting straight in the car when installed? It might seem as the rotor is not pointing upwards, but it is compared to the engine!! not compared to gravity. The rotor appears to be pointing a bit to the left when watching it and not considering engine tilt.
The easiest way to find that all is well:
The number one cylinder need to be at the top of its travel (TDC). If you can not see any markings for this. Just put a long screwdriver through the spark plug hole and rotate the engine. This way wou can feel exactly when the piston reaches its top dead center. Then you make sure your cam drive is in the right position by checking the markings. Put timing belt on and your set to go.
Regards:
Eirik Kvello-Aune
www.diateam.no/porsche
40 degrees is about the tilt of the engine when mounted in the car. I hope you did not think the referance point is gravity (straight up or down).
The 968 workshop manual matches our two 968 engines perfectly. Did you remember that the engine is not sitting straight in the car when installed? It might seem as the rotor is not pointing upwards, but it is compared to the engine!! not compared to gravity. The rotor appears to be pointing a bit to the left when watching it and not considering engine tilt.
The easiest way to find that all is well:
The number one cylinder need to be at the top of its travel (TDC). If you can not see any markings for this. Just put a long screwdriver through the spark plug hole and rotate the engine. This way wou can feel exactly when the piston reaches its top dead center. Then you make sure your cam drive is in the right position by checking the markings. Put timing belt on and your set to go.
Regards:
Eirik Kvello-Aune
www.diateam.no/porsche
Last edited by mmmbeer; 12-03-2003 at 04:47 AM.