can't find TDC for cam timing PICS please!

[Yellowbird RS]

please pics to find TDC cam timing in 1974 carrera

[Tyson Schmidt]

I don't have pics, but you line up the z1 mark with the split in the case.

[126coupe]

Get a flashlight and a mirror have a friend turn the engine by hand.................its there Z1 on the pulley and a slash mark on the fan housing dont forget to mark both for future reference

[Hugh R]

I don't know pcars too well, but on other cars, I use a dial gauge in the NO. 1 spark plug hole to find TDC

[911pcars]

The Z1 mark is pretty close to TDC. Not sure how the factory determines exact TDC on every engine. A mark at the same location on every pulley would be pretty close on most; maybe not so close on others.

I think everyone agrees it's pretty important to know since the cams (and ignition timing) use TDC as a reference point.

I'd recommend doing this with the cyl. head off the engine, as in during a rebuild or when you're in this area of the engine. Fabricate a piece of metal held on by the case studs into the cylinder so that as you rotate the engine by hand, the mechanical stop will stop the piston at some point near TDC. At this point, stop and mark the pulley.

Reverse the direction of rotation until the piston butts up against the stop again. Mark the pulley. You now have two marks. Halfway between them is true TDC for your engine. File a notch in your pulley to mark it, then paint it white to differentiate from the factory TDC notch.

On certain engines, one could make a mechanical stop- TDC tool out of a hollowed out and internally threaded spark plug, but I'm not sure there's enough clearance for a hunk of metal in the chamber due to the opening/closing intake/exhaust valves as the engine rotates.

Sherwood
http://members.rennlist.org/911pcars

[RoninLB]

Originally posted by 911pcars
one could make a mechanical stop- TDC tool out of a hollowed out and internally threaded spark plug, but I'm not sure there's enough clearance for a hunk of metal in the chamber due to the opening/closing intake/exhaust valves as the engine rotates.

"I'm not sure there's enough clearance for a hunk of metal in the chamber due to the opening/closing intake/exhaust valves as the engine rotates."
--- I don't recommend what I did because it was a WTF/ why not.

I cut about 3/4in of 1/8 copper tubing and attached a length of safety wire. It was attached so it would slip into and out of plug hole. I did the routine at TDC where both valves are closed. re-played a couple of times to confirm factory TDC. It's a lousy way of confirming TDC

[Early_S_Man]

For the spark plug hole confirmation method to work properly, you need a long, threaded extension for a dial indicator plunger with a round tip, and a spark plug body with a brazed-on guide bushing that fits the extension precisely. There shouldn't be any slop or binding any where along the path of the full range of dial indicator travel ... a spare cylinder head can/should be used for testing of the dial indicator travel with the guide/spark plug insert and extension!

Luckily ... you only have to use this method on cylinders #1 and #4!

[911pcars]

May be splitting hairs, but IMO using anything less than a positive mechanical stop is less accurate. The crank can move quite a number of degrees while the piston is apparently at TDC. In addition, due to engine friction, it's more difficult to move the crank just another 1º to see if the piston is just before, at or just past TDC.

However, any of the suggested methods is better than assuming the mark is correct. I don't have enough of a database to know if the factory method is both consistent and accurate for all their production engines.

Sherwood

[Matt_'77_2.7]

Is it true that Porsche engines aren't supposed to be rotated backwards? If so, why not?

I have a tool from the Chevy SB days that you extend into the #1 spark plug hole. rotate the engine CW mark the pulley when it stops. Rotate it CCW until it stops mark pulley again. TDC is halfway in between two marks. Worked well on non Porsche engines.

Matt