Tdc

[philip j]

Just want to make sure I'm using the correct TDC mark. I have a 87/930. The 2 marks close together are; 1st to the right, 5* BTDC, and to the left is TDC. I have so far seen 3 different configurations in my search, and Bruce Anderson's engine rebuilding book. thanks Philip

[Ronnie's.930]

You are correct. I just looked at mine to double check and the left hand mark is the one that is inline with the fan housing index mark when the rotor is pointing at the index mark on the distributor housing . . .

[fredmeister]

There should be a Z1 mark which is TDC. Also, look for a mark 180 degrees across the pulley center as usually there are marks every 120 degrees on the pulley too. this might help to sort which one of the three marks close together are true TDC.

[Ronnie's.930]

No Z1 mark on the 87 a/c double pulely . . .

[JFairman]

There is a Z1 TDC mark on every 911 or 930 pulley I've ever seen.

You need that mark to time the cams. There is also a 26 degree BTDC mark and a mark every 120 degrees after Z1 TDC to get TDC on the other cylinders in firing order while adjusting the valve clearances.

[Ronnie's.930]

On mine, the hash mark for TDC is there(as well as the other marks you indicate), but no Z1 script like I have seen on other pulleys . . . This is a 1987, and as far as I know, the pulley is OEM (double, A/C version).

[mark houghton]

Originally Posted by Ronnie's.930

On mine, the hash mark for TDC is there(as well as the other marks you indicate), but no Z1 script like I have seen on other pulleys . . . This is a 1987, and as far as I know, the pulley is OEM (double, A/C version).

Z1/TDC....the same thing. Z1 in the Mother Language means "der zoomenheimer". My '87 doesn't have anything other than hash marks to indicate "Z" or top dead center. Also, I slapped a degree wheel on the pulley to clock out each degree of timing. Mo' info is mo' betta......

[philip j]

Now it's making sense. The mark to the right of TDC is 26* BTDC. I thought it was kinda far away to be 5*. This must have been a mark for setting the stock timing. Philip

[Traveller]

Originally Posted by philip j

Now it's making sense. The mark to the right of TDC is 26* BTDC. I thought it was kinda far away to be 5*. This must have been a mark for setting the stock timing. Philip

Phil, I sent you the following PM a few minutes ago and now just came across this thread.

Hi Phil,

I was just thinking about it, but I think that second timing mark, the one without any white on it is the advance mark and not the 5 degree mark.

Your engine may be timed too advanced and that is why it is hard to start.

Furthermore, with dual plugs, you need to retard ignition timing both at idle and reduce the advance as well because you have two flame fronts causing the whole burning process to complete sooner which means you can start the spark or initial point of ignition later. I remember doing the numbers for a BMW motorcycle that went from a single to a dual plug.

If you can measure the diameter of your engine pulley, I can confirm what those marks are. I need the outer edge diameter.

Lets say your pulley diameter is 6 inches. The circumference would be pi * D or 22/7 * 6 = 18.86 inches.

For a 10 degree angle... 18.86 / 36 = about a half inch along the pulley edge. So a 5 degree mark would be 0.25 inches from the TDC mark.

I would want to know how MSD controls the ignition advance and if it is adjustable.

[s5uewf]

My 1988 only had 2 marks on the pulley, too. I believe Porsche must have changed the way they marked the pulleys to encourage testing and setting properly for the EPA.

I think the right mark was the timing mark to set against with distributor ports blocked and engine revs adequate for full advance - though it is a bit foggy at this point since I set it a while ago.

[JFairman]

"I think the right mark was the timing mark to set against with distributor ports blocked and engine revs adequate for full advance - though it is a bit foggy at this point since I set it a while ago."

Yes, it is the #1 cylinder 26 degrees before top dead center mark and the instructions to use it on a USA car are on a sticker on the inside of the engine lid to refresh your memory. Open it, look up in there and the sticker with tuning and valve clearance specs are above the AC compressor location.

There's no need to plug the vacuum lines when removing them from the distributor vacuum pots to check distributor centrifical advance on a CIS 930 motor. That will have zero effect on centrifical advance.

[philip j]

for stock timing. I have a Jarvis Tech 12 plug distributer. I need 28* @ 4000 rpm. thanks for the info, knowing what the hash mark is, I now have a starting point. Philip

[Jim2]

Philip, a little late with this but if you ever need to verify TDC 1 remove the spark plug and insert a straight stiff piece of wire about 5" long so it's resting on the piston crown then turn the crank pulley back and forth with a breaker bar and you will definitively be able to feel TDC with your fingers holding the wire.

[JFairman]

Originally Posted by Jim2

Philip, a little late with this but if you ever need to verify TDC 1 remove the spark plug and insert a straight stiff piece of wire about 5" long so it's resting on the piston crown then turn the crank pulley back and forth with a breaker bar and you will definitively be able to feel TDC with your fingers holding the wire.

A pencil works good for that too.
As you turn the crank back and forth a little while watching the Z1 mark you'll notice the crank has a small window of turning back and forth where the pencil or wire won't move down at all. The Z1 mark on the pulley should be right in the middle of that window.
If the window of crank movement is more than around 10mm - 12mm before the piston at TDC and pencil or wire starts to move downward it's sighn that rod bearing is possibly worn.

[philip j]

This is a new bulid, with about 20 min on it so far. Just waiting for the snow to melt, Just put the back bumper on it today. It will soon be DRIVIN SEASON Philip