Installing Pertronix Ign II on a stock 2.0 engine the Distributor appears to be stock vac unit.

after putting the rotor on top the cap doesn't seat.

Any ideas?

You probably don’t have the magnet far enough down the distributor shaft. While it looks like it fits on the cam on the distributor in any direction, that’s not the case. It only fits in one position. When it fits correctly it will push quite a way down over the cam. That allows the rotor to push all the way down onto the shaft. Which will allow the distributor cap to fit correctly.

Hope this helps.

Just takes some downward force. The fit tighter than socks on a rooster.

First Ignitor 1 I fitted the magnet piece was too tight,I found a little clearancing inside and it pushed on but was still bloody firm.
I've never had that issue with Ignitor II or other brands.

We install many compufire units and on most we grind the bottom of the rotor on a belt sander to get the cap to seat correctly.

I've also had this experience and found that twisting the magnet laterally at the same time as pushing down on the distributor shaft would get it to seat a little lower, even when it appeared that the cam lobes were lined up with the recesses on the inside of the magnet perfectly to begin with.

Thanks guys, finally went on...