Distributor and TDC

[kidporsche911]

I've been search and trying to understand the TDC, I need to pose this question. I'm trying not to screw things up. I have a 1977 Targa. Bought it and it hasn't been touched accept for minor stuff.

I'm doing a tune up and after replacing the distributor the vehicle wont' start. It'll run rough for a little whole then dye. After researching and comparing my Distributor notch and TDC #1. It looks off to me. Can anyone confirm, based on my pic.

[kidporsche911]

Couldn't upload picture so trying this method. lol

[Walter_Middie]

kidporsche911,

You need 3 things:
1.) crank pulley lined up with TDC
2.) distributor rotor pointed where spark plug wire for cylinder #1 will be once the distributor cap is put on
3.) The engine on the compression stroke for cylinder #1. This is where most get it wrong. The cam and distributor are geared so that they turn half as fast as the crank. So the crank turns around twice in the time that the distributor turns once, and TDC happens at 2 different times for one complete cycle of the engine. Once with cylinder #4 at TDC, and once with cylinder #1 at TDC. You want #1 at TDC. This can be verified several ways, but the easiest is to remove the upper valve cover and ensure that the #1 intake valve is not tight - that the rocker arm is slightly loose. This will tell you that #1 is on the compression stroke.

Here is a cartoon of what your crank pulley should look like:



Here is a picture of the distributor with the rotor pointing at plug #1:

[Walter_Middie]

To move your rotor - set crank pulley at TDC and pull up on the distributor just enough so that the rotor will turn - about an inch. Push the distributor back in once the rotor is lined up with the mark - or close to it. The rotor will move slightly when you push the distributor back in. Trial and error are your friend here.

[Bill Verburg]

Originally Posted by kidporsche911

I've been search and trying to understand the TDC, I need to pose this question. I'm trying not to screw things up. I have a 1977 Targa. Bought it and it hasn't been touched accept for minor stuff.

I'm doing a tune up and after replacing the distributor the vehicle wont' start. It'll run rough for a little whole then dye. After researching and comparing my Distributor notch and TDC #1. It looks off to me. Can anyone confirm, based on my pic.

be sure that you are at TDC on the compression stroke.

each cylinder has 2 TDCs
one at the end of the compression stroke where both valves are closed
and one at the end of the exhaust stroke where both valves are a bit off their respective seats(overlap)

[kidporsche911]

Got it. Im a newbie and working on a few different things at time. When things happen they happen in 3's.
My original question is because I thought my TDC may have been off. This was helpful because I'm upgrading to new Ignition distributor in a few weeks and will follow your steps.

My distributor clips on the side just broke off and I need to replace it.
If I removed the Ignition distributor to replace clips and put it right back in without starting or moving the car, will it stay aligned within the TDC.

[boyt911sc]

Originally Posted by kidporsche911

Got it. Im a newbie and working on a few different things at time. When things happen they happen in 3's.
My original question is because I thought my TDC may have been off. This was helpful because I'm upgrading to new Ignition distributor in a few weeks and will follow your steps.

My distributor clips on the side just broke off and I need to replace it.
If I removed the Ignition distributor to replace clips and put it right back in without starting or moving the car, will it stay aligned within the TDC.

Kid,

Most likely not unless you were very lucky. Set your crankshaft pulley @ Z1 with rotor pointing to the scribed marker on the distributor body. Refer to Rex’s picture. Read and understand post #4. Double check your work by repeatedly cranking the pulley back @ Z1 (rotor pointing toward #1). Adjust left or right as needed. Use an inductive timing light to set you ignition timing. Keep us posted.

Tony

[JSV798]

I lost the timing on my 78SC a few months back; when pulley mark Z1 is at TDC you don't know whether it's #1 or #4 on compression. I decided to remove the valve cover over the right-hand bank as there is less in the way and then check that that the valve clearance on #4 is NOT slack. If there is slight play (looseness) then #4 is at TDC and you need to rotate the crankshaft pulley 360 deg to get it back to Z1 (in clockwise direction only as viewed from the rear) to get TDC on #1. Distributor should then be set pointing to #1 spark plug as before (there is a small notch in the distributor body it should point to).

[kidporsche911]

Thank you everyone for the advice's. Still working on this. I'm searching how to remove the brackets to get to the crankshaft.

It looks like a *****. Stupid question, because my starting issue may not be the timing. I took pics of the notches. Can you tell by the pictures on the notch location if its off?

I'm guessing not!! But had to ask.

[kidporsche911]

[Bill Verburg]

Originally Posted by kidporsche911

The 2 notches are probably 5°ATDC(left) & TDC(right)

Here is a timing TSB, your '77 is on the far right

[Trackrash]

Looks like 30 35 BTDC to me. How can you tell? Should there be a Z1 stamped on the pulley?

[Bill Verburg]

Originally Posted by Trackrash

Looks like 30 35 BTDC to me. How can you tell? Should there be a Z1 stamped on the pulley?

That could be too

[JSV798]

There will be a Z1 on the front face of the pulley, the side facing the back of the car; I have to use a mirror and a light to see it!

[JSV798]

Should have also said there are two other marks 120 deg apart; again I have to use a light and a mirror to see them but they don't have Z1 stamped by them. In other words there are 3 marks on the face 120 deg apart for use when setting valve clearances and one of them is marked Z1 (TDC) at least on my car.

[JSV798]

The 2 notches on the pulley in your photo are where you should find Z1 on the face so you are nearly at TDC (see Bill's post on markings) and it looks like from Bill's diagrams that the of the notches in the pulley the one nearest the mark I can see on the fan casing will be TDC so there should be a Z1 on the face - it can be hard to see; get a light and mirror on it.

[frosty2]

Yes on mine the Z1 is stamped on the back side of the pulley so I have to slide my mirror down between the pulley and the engine

[kidporsche911]

Thank you. I'll do what I can and post an update. Been reading alot and get confused, but discovering alot.

[kidporsche911]

Originally Posted by Bill Verburg

The 2 notches are probably 5°ATDC(left) & TDC(right)

Here is a timing TSB, your '77 is on the far right

Nice chart

[kidporsche911]

Originally Posted by Trackrash

Looks like 30 35 BTDC to me. How can you tell? Should there be a Z1 stamped on the pulley?

I'm troubleshooting starting issue. I've never touched or pulled up the entire Bosch distributor. So I'm hoping its not a TDC issue. So based on the pic and 30-35 does it look correct to you???

The only thing I did was change the cap and rotors. I did miss the notch on the cap, which I've since corrected.

I'll have to check my points but don't have the tool yet.