crank position/cam timing
12-02-2003, 11:57 PM
#1
Intermediate
Thread Starter
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, 03:14 AM
#2
Race Car
Read 15-5 under ‘Checking and adjusting the camshaft setting’ in your 968 workshop manual and I think you will find some clues. Perhaps somebody [previous owner, mechanic, other] removed the central camshaft bolt from your exhaust cam without using 3 m5x15 bolts to keep the cam gear from turning RELATIVE to the exhaust camshaft?
It sounds like your cams and engine are aligned just fine [since you’ve been driving the car], but the mark on the cam gear is not lining up with the mark on the rear belt cover [in your case of assuming the cam gear is correct and lining it up with the mark on the belt cover, the crank and camshafts themselves are off of the cam gear mark]. This is why you should always trust the CRANKSHAFT TDC mark more than the CAM TDC mark.
I don’t want to speculate about why the gear is not properly aligned with the camshafts [and therefore the rest of the engine] but do you have any records of camshaft, Variocam, or cylinder head replacement from the previous owner? Perhaps it was just a timing adjustment done improperly/incompletely.
A Tiptronic engine isn’t aligned any differently. The flywheel TDC marks may be different though I’m not sure. Here’s how the TDC mark looks on a manual transmission 968 [w/ dual mass flywheel]:
There should be two ways of verifying the crank is at top dead center [piston #1 at firing TDC, piston #4 at intake TDC]:
- Align the mark on the flywheel to the one on the center hole of the alignment plate.
- As you did, use a dial gauge to get piston #1 to FIRING TDC [valves completely shut].
At this point the timing belt inspection plug on the distributor housing should be removed and the mark on the cam gear should be perfectly aligned with the etching on the rear belt cover: If it’s not aligned and the engine has been running okay this way then your cam gear was moved and wasn’t locked down properly when the camshafts were timed.
Now here is the drawing to which you're referring from the Porsche workshop manual:
The cam timing mark is not @ 40 degrees after TDC. The timing mark is at TOP DEAD CENTER, not before or after. The ignition rotor in the workshop manual is oriented just as you describe on your car, only difference is the illustration in the manual has the engine out of the car [more upright] and yours is in the car sitting at a slant. If the engine in the drawings was installed in the car then it would have the timing mark straight up and the rotor ~40 degrees before that just as you describe, but the timing mark IS NOT 40 degrees after TDC. The timing mark SHOULD BE TDC.
It sounds like your cams and engine are aligned just fine [since you’ve been driving the car], but the mark on the cam gear is not lining up with the mark on the rear belt cover [in your case of assuming the cam gear is correct and lining it up with the mark on the belt cover, the crank and camshafts themselves are off of the cam gear mark]. This is why you should always trust the CRANKSHAFT TDC mark more than the CAM TDC mark.
I don’t want to speculate about why the gear is not properly aligned with the camshafts [and therefore the rest of the engine] but do you have any records of camshaft, Variocam, or cylinder head replacement from the previous owner? Perhaps it was just a timing adjustment done improperly/incompletely.
A Tiptronic engine isn’t aligned any differently. The flywheel TDC marks may be different though I’m not sure. Here’s how the TDC mark looks on a manual transmission 968 [w/ dual mass flywheel]:
There should be two ways of verifying the crank is at top dead center [piston #1 at firing TDC, piston #4 at intake TDC]:
- Align the mark on the flywheel to the one on the center hole of the alignment plate.
- As you did, use a dial gauge to get piston #1 to FIRING TDC [valves completely shut].
At this point the timing belt inspection plug on the distributor housing should be removed and the mark on the cam gear should be perfectly aligned with the etching on the rear belt cover: If it’s not aligned and the engine has been running okay this way then your cam gear was moved and wasn’t locked down properly when the camshafts were timed.
Now here is the drawing to which you're referring from the Porsche workshop manual:
The cam timing mark is not @ 40 degrees after TDC. The timing mark is at TOP DEAD CENTER, not before or after. The ignition rotor in the workshop manual is oriented just as you describe on your car, only difference is the illustration in the manual has the engine out of the car [more upright] and yours is in the car sitting at a slant. If the engine in the drawings was installed in the car then it would have the timing mark straight up and the rotor ~40 degrees before that just as you describe, but the timing mark IS NOT 40 degrees after TDC. The timing mark SHOULD BE TDC.
Last edited by PorscheG96; 12-03-2003 at 03:44 AM.
