I need to add timing marks to my pulley that I made. It's not the same diameter as the stock pulley so i need to find and mark TDC first. Sooo.....

I set my 12a to TDC using a proven but not exact method. I have a light weight flywheel so I put the large side of the counter weight to the passenger side at 9 o'clock looking from the front of the car. Then I bolted on a stock pulley to confirm I set it right.

The pointer is just past the first notch on the stock pulley. Given that the stock pulley marks are at 5* and 20*, I'm guessing if it's past the 5* mark, it's closer to 10*. Or am I missing something?

Should I trust the pulley and mark it 5* before the first mark to find TDC and set the pointer to that?

Basically i am looking for a more exact method so I can mark my new pulley. I also do not like the chop sticks in the spark plug hole way. I have used it before, and I find it to be even less accurate.

 

you can take the crank pulley bolt off and move the pulley so the key stock is at the 9 o'clock position (aiming at the exhaust side of things)

 

Take the diameter of the factory pulley and the the diameter of your homemade pulley and calculate the percent difference (ratio). Now measure the distance between the factory timing marks. Take the ratio in the first calculation times the distance of the factory timing marks. This will be the distance between marks on the new pulley.

 

To find tdc, remove the top inspection plate and make sure the rear counterweights half moon is facing the exhaust as shown below

 

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I understand that. But I can easily be 5* or more off with this method. My eye might see it differently from the next guy. I'm trying to be exact as possible so I can mark my custom pulley 0* TDC.

I'll probably just trust the stock pulley. So 5* before the first mark will be TDC correct?

 

Another, and easier, way to mark the new pulley is to take the diameter of the pulley and divide it by 360. This measurement will be 1 degree.

 

Yes you are correct, but you must have a starting point. TDC is this starting point.

 

So here's what I did. I marked the stock pulley 5* (5mm) back from the first notch. This should be TDC (My 0* point) and use this pulley as my TDC finder from here on out.

1st pic is at first mark on stock pulley. (5* advanced)

2nd pic is 5mm before notch at my new TDC notch.

 

so I milled a slot and a divot to indicate TDC. All the rest of the degree marks will be much thinner and done on a rotary table so I can be exact.

here's a shot to show what I mean.

 

The pulley and hub have to be a factory matched set. Otherwise if you mix and match, they could be off by as much as 7 degrees.

 

I set TDC visually by checking the apex seals of the rear rotor passing through the leading and trailing plug holes.


Here is the procedure I used:
Remove both rear rotor spark plugs.
Rotate the crank until you can see an apex seal (tip of the rotor) in the trailing spark hole. The trailing plug hole is restricted, making the seal somewhat difficult to see. Use a flexible light and a mirror. When the seal is seen, mark the crank.
Rotate the crank until you see the same apex seal in the leading spark plug hole. This plug hole is not restricted, which makes it easy to see the seal. Mark the crank.
Halfway between your two marks is TDC for the front rotor (#1) rotor.

 

I never heard this before. Have you ever personally confirmed this?

I have a few stock pulleys. I'll try a few out and see if there's any difference.

 

On a 12-A the 0 notch on the pulley sit right above the 10mm bolt @ 12:00 provided that the engine is at tdc

 

I can also confirm this on a GSL-SE also. I just removed my pulleys by aligning the leading mark (yellow mark on pulley) and one of the 10mm bolts holes was at 12:00. I like to put a bolt back in this hole just in case the engine for some reason gets rotated with the pulleys off.

 

 

The 1979 had an aluminum rivet that is mushroomed. Even if the rivet is missing, you can align rivet hole.

 

Yes, I saw that and believe the pulley hole to be in the mushroomed rivet. That's why I'm confused. It seems to me that my only option would be to rotate the pulley 180 degrees to hit the other rivet hole, when visually it appears that I only need to clock it 15-20 degrees to hit the next bolt hole, which would align the pointer to my yellow timing mark. Is the lower 3 belt pulley two pieces that the rivet keeps in alignemnt, or is the rivet actually part the pulley-to-crank mounting flange? I'll look closer this weekend.