How Do I Find TDC to Adjust Valves

Don Ivey · 10-18-2010, 12:31 PM

I've done this before, but this time I'm having trouble verifying that I have TDC on the Number one cylinder. There is no Z1 mark on my pulley, so I'm not sure the best way to find TDC. On my motorcyeles, I just take out the number one spark plug, put my thumb over the hole, and turn the engine until I feel the compression, then look for the appropriate timing line. I thought I was ok today with the Porsche, but when I got to number two cylinder (one and six seemed to go fine) the exhaust valve was tight, and when i tried to loosen it, I could never get it loose enough to turn the pushrod with my finger. This is an '87 911 BTW, and the car was running fine so I think I'm doing something wrong. Thanks in advance,

Don Ivey
'87 Carrera
'83 Moto Guzzi

Jesse16 · Jesse16's Garage

Just did my 87 Carrera and I started with a similar issue. You've got to look at the fan pulley, not the AC pulley. Also, I could see no "z1", just the marks. Just to make it fun, I have "two" notches about 1/2" apart in the vicinity of z1. Some one had added a mark sometime in my cars history. You actually have 3 marks at 120 degrees apart (plus my extra mark). I put a dab of whiteout on the other two and then interpolated which of the two I had that is actually 120 degrees away. At that point, the distributor rotor looked right, pointing at #1 so off I went on valve adjusting. Seems to have worked out fine, car is running great and I learned alot.

Don Ivey · 10-18-2010, 12:55 PM

Thanks for your comments, Jessie. I have removed my A/C, and still have the A/C pulley, but it has no marks for timing. Would I be right in assuming that at one Z1 point, my valves would both be loose on number one, and on the next iteration of Z1 mark, both valves on cylinder one would not be loose? Thanks,

Don IVey

lindy 911 · lindy 911's Garage

I have never used the Z-1 mark or TDC for that matter when adjusting rockers. If you turn the motor so the cam lobe is away from the rocker you are OK to adjust. I have done this for years on all sorts of engines without problems.

Lindy

Wil Ferch · 10-18-2010, 01:45 PM

Whenever this question comes up, I like this pic---->

930 Timing Marks For Valve Adjustment

Jesse16 · Jesse16's Garage

Will's photo is very explanatory. My TDC was the left mark as in his photo. Your pulley must have 3 or 4 notches, doesn't it ? At TDC with the rotor at #1, the rockers will/should be loose usually. Then just adjust. Use the procedure of your choosing found on Pelican and don't overthink it until you're sure you're doing it right. There are lots of shortcuts and of course you can adjust other valves at each position if you care to keep track carefully. My 2 cents.

Rot 911 · 10-18-2010, 02:37 PM

Will's picture is correct for the 3.2 engine.

rusnak · 10-18-2010, 03:01 PM

The 3.2 has fewer timing marks than an SC, so less confusion.

Look for the second of the two that are close together, then pull on the rocker arms to verify they are loose and visually check that the dizzy rotor is pointing to #1 cyl.

gtc · gtc's Garage

+1 to what rusnak said. Pull the distributor cap, remove the dust shield, then replace the rotor and turn the engine until the rotor points to the TDC mark on the distributor body.

2.70Racer · 10-18-2010, 06:37 PM

Remember it is not required to be exactly on any one of the three TDC marks to adjust the valves for each cylinder.
The intake and exhaust valves have been closed for over 100 degrees and will ba closed for over 100 degrees prior to and after TDC.
Get a flashlight and be sure the rocker is riding on the base circle. Then adjust.