New Rotor + Cap and it won't fit on!

[OsoMoore]

On my SC, I was having some issues with my old rotor/cap and they were showing corrosion and such, so I bought a new Bosch rotor and cap.

Distributor caps have a tab that fits into a notch on the distributor itself. With my old cap, the tab was worn down on one side, and the cap would rotate a few degrees within the notch.

However the new cap won't fit all the way over the distributor. I think it is bottoming out on the top of the rotor, because if I take out the rotor, the cap fits on fine and snugly.

Old Cap + Old Rotor = Cap fits but wiggles (presumably due to worn cap tab)
New Cap + New Rotor = Cap's tab doesn't lock into the notch
New Cap + Old Rotor = Same as w/ new Rotor
New Cap + No Rotor = Cap fits snugly and properly

I measured the depth of the two caps with my carpenter's combination square, and they seemed the same. The rotors are exactly the same height.

Is it possible I'm not pushing the rotor down hard enough? I'm hesitant to apply too much pressure to the rotor, and it seems to be going on a fair way. I only had a few minutes before work today, so I can fiddle with it more later. I'll see if the old cap fits differently with no rotor underneath it.

Any ideas are appreciated.

[wolds]

Chances are good you didn't seat the new rotor all the way down. What are the part numbers on the new R&C?

[T77911S]

the caps do wiggle just a little.

agree with rotor not on all the way. give the rotor a twist to make sure it is locked on. you try a dab of grease to help it go on if it is hard

[CCM911]

Spin the new rotor as you apply downward pressure. Once the rotor finds the notch in the shaft, it will slide right down.

[Targalid]

Look inside the rotor cavity. There is a sloped key that must fit in the slot of the metal shaft of the distributor. Look at it, place the rotor exactly with the key and the slot aligned, then press down and it will slide, with some difficulty, into place.

[wwest]

The other day I checked the rotor and cap in my '78 with an eye to taking pctures for your benefit.

But my cap was so different from your pictures that I decided there had probably been a model year distributer change.

On second thought, did some PO change your distributor out for another MY?

[wwest]

Pictures of internals of distributer with rotor/cap removed?

Did you buy rotor/cap from Porsche dealer parts department?

There is history of 911 owners being sold a mismatch, especially rotor, confusion there...

[OsoMoore]

Originally Posted by wwest

Pictures of internals of distributer with rotor/cap removed?

Did you buy rotor/cap from Porsche dealer parts department?

There is history of 911 owners being sold a mismatch, especially rotor, confusion there...

I'll take some pictures tonight, in addition to ensuring the rotor is fully on. I have records as well so I should be able to determine when it was last replaced.

I obtained the parts from BumperToBumper, because they were able to get them the next day. They are Bosch. I'll check the exact part number when I get home.

Thanks for all the help!

[tirwin]

I was assembling my engine last night so I just did this. When you put the rotor on it should snap into place. I had to push down reasonably hard and wiggle it a bit to hear and feel solid contact. It wasn't terribly hard but it was more than just a light push.

[wwest]

According to your pictures the old rotor was "riding" low.

The carbon arc path/trail on my distributor cap copper "contact" point is at the midpoint, whereas yours seems to be at the VERY bottom. Also bothered by the apparent physical scratches on the cap in line with the rotor tip.

[wwest]

Make sure there is not much up/down travel of the distributor cam, under that cotton wadding should be a snap ring to lock it into place vertically.

[OsoMoore]

I had the rotor turned wrong. I had mistaken a spline on one side of the distributor shaft for the gap where the notch fits. A couple minutes in good light with the dust cover off and it all became clear.

[Bob Kontak]

Cool beans.