Badly Scored Distributor Cap - Help 1989 S4
 

I recently changed out all ignition parts but when I started her back up there was a significant knock/scraping noise from the right distributor cap. By the time I turned the engine off(10 seconds) the noise was pretty much gone. Tune up worked great, lots more power. Case closed.

Last week I decided to look at what had caused the noise and found a badly scored distributor contacts on 3 of the 4 posts with the middle the worst. Along with brass shavings. I double checked fitment and all looked fine. I figured I had a poorly manufactured Distributor cap. Got a new cap and rotor and got the same problem.

There does not appear to be a way to put things back together off-center but from the wear pattern that sure looks like something is off center by 1/32" to 1/16”.

The timing belt was done 5 months ago and I never heard the knock or bothered to check the old distributor before I replaced it.

Any ideas?

It is possible that you are missing a locating pin/bolt for that cover.

Cam cover not correctly installed/seated? Backing plate for cam cover is loose? Broken cam shaft nose? What brand are the rotor and cap? Only so many possibilities to get the two mis-aligned.

Mike

I've caused that on the driver's side by not seating the inspection cover properly.

take the cover off and make sure the the 2 hollow roll pins are sticking out from either the rear cover or the front cover so the front cover will be aligned when fitted .

These are spring steel roll pins that have the bolts passing through them,
its possible for one or both to get pressed into either part of the either cover and then get pressed flat so they dont hold the cover perfectly straight,
based on your findings i would say it probably the top roll pin thats not in the correct position

Thanks, lots of things to inspect on the tear down tomorrow. It's reassuring that there are possibilities beyond me hosing things up.

It is possible that you are missing a locating pin/bolt for that cover.

NC928S4-> There are no pins that I see. The Rotor can only fit one way. The Cap has to fit so wires connect. So I don't think I screwed that up.

Cam cover not correctly installed/seated? Backing plate for cam cover is loose? Broken cam shaft nose? What brand are the rotor and cap? Only so many possibilities to get the two mis-aligned.

NC928S4-> Will check. All stuff was Bosch from 928sRUs who also gave me replacement parts no questions asked.

I've caused that on the driver's side by not seating the inspection cover properly.

NC928S4-> More to check thanks.

take the cover off and make sure the the 2 hollow roll pins are sticking out from either the rear cover or the front cover so the front cover will be aligned when fitted .

These are spring steel roll pins that have the bolts passing through them,
its possible for one or both to get pressed into either part of the either cover and then get pressed flat so they dont hold the cover perfectly straight,
based on your findings i would say it probably the top roll pin thats not in the correct position.

NC928S4-> Thanks Merlin. Will check.

the roll pins locate the tbelt cover......take it off and inpsect as well as the rotor

FOUND THE PROBLEM! This engine must have come from another car that had been in a pretty serious accident. This is incredible but the block has a repaired crack (welded) all the way around the bell housing area! That was the first clue. To find out why the dist. cap was getting scored as described above, we removed the T-belt, cam sprocket and right side rear half of the T-belt housing, cleaned it, and noticed the crack. This was evidently caused by a frontal impact of the engine. Who'da thunk it!

This thread is......

...useless without...

:icon501::banghead::crying:

Wow! I'd like to see pictures of that.

So, is the current problem due to the weld bead holding the backing plate off kilter? The bellhousing is a long way from the cam nose.

Yea, i wanna see some pictures of this. Very odd.

Ray,
Having seen pictures of the crack on the rear cover it does not look like it would move. If it is cracked it may also be bent out of shape causing the misalignment of the cap.
Roger

It's also possible that they just dropped the engine when it was out of the car.

So this is my car and I have pictures. In addition to the "crack" in the photos the back plate is also bent slightly from who knows what of the various POs. At first inspection using 50+ year old eyes you don't notice the bend. The deflection/bend is very minor as evidenced by the wear pattern on top of the rotor. The left side rotor which works perfectly has a "point" wear pattern whereas the problem right side shows a 3/32" diameter circular pattern(no photo until next week). This pointed to an off center distributor mounting. So splitting the diameter of the wear pattern as the offset of rotation it didn't take much of a bend from approximately 3 inches away on the backplate to cause the mount point of the distributor cap to be off.

Anyway, 928intl has replacement back plate and front cover on route. Thanks Mark, for extending the 50% holiday discount before the special actually started. Also, thanks to Roger for extending new parts to isolate the problem. I have NOT had this much fun and expense since my last root canal.

So, crack in the block, welded, as well as a crack in the backplate. Wow.