Replacing a matching distributor

I have an 83 Lincoln Towncar with 170,000 miles. I am about to replace my distributor (this one is simple, with no vacuum, no wires). The original one is completely worn, and I can giggle it back and forth! Before I pulled out the original, I marked the side of the distributor cap so I can match the location of the rotor when replacing the distributor. I have a complete match replacement for the distributor, but when I am going to replace the distributor, the rotor does not line up in the same location as the previous distributor. It seems to be advanced a mere 5%. Since the original was all worn out and loose, is this 5% advancement expected? Why wouldn't the replacement distributor align the rotor in the same place as the original? What problems will I run into if I leave the rotor in the 5% advanced location? I need to get this back in right away and get the car running again quickly.

Thanks! Rob

There are several potential explainations. First of all, since your old one was worn its possible that the oil pump drive pin in the bottom was also worn. Now that you're trying to put a better unit in, it might not be lining up with the oil pump. You know what you need to do; get the distributor back one tooth so its in its original orientation. The solution is super simple. Stick a long screwdriver down in there and turn the oil pump shaft so that the slot for the distributor drive gear allows you to slide it home in the right position on the right tooth.

Double check this before you do it, but most later distributors (most of my experience is with GM) don't care where you install them, as long as you rotate the housing to provide the proper advance. Old points systems required being on the right tooth so that the points open and close corresponding to the right time. Later distributors don't require that since they use a different triggering system.

I just installed my HEI on a 454 about 160 degrees from stock so I could consolidate vacuum lines and make a cleaner installation. Since the HEI has 8 triggers and 8 pickups, it doesn't matter what "tooth" its on. I'm pretty certain that Fords are the same, meaning you could leave it as is and rotate the housing but double check it with a Ford-smart person.

Get a timing light and do it properly. Timing lights are fairly cheap, ~$25.

Update: I replaced the distributor by placing the rotor at 5 degrees advanced from the original mark. There was no issue with the oil pump. The starting problem I was working on was not related to the distributor, but it needed to be replaced. The car is running after I replaced the EEC relay, and it is not pinging. Thanks for the replies.

- Rob

83lincoln, are we talking about an EEC-III system with crank trigger?