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Rotor Rubbing on Inside of Distributor Cap

Posted by Jon Zaremba 
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Jon Zaremba Avatar
Victorville, CA, USA   usa
1979 MG MGB "Brian"
Hey There...

While trying to determine what is causing an occaisional miss in my timing, i noticed that on the inside of the distributor cap, there was some wear. Looked at the "blade" part of the rotor, and there was some black plastic!

This is a brand new cap and rotor, and they appear to disagree with eachother. Has anyone seen this before? Could a little bit of friction like this cause significant timing issues?


Jon Zaremba

BManBrian67 Avatar
Brian M
HB, California, USA   usa
1967 MG MGB MkI "MI MG"
2000 Porsche Boxster S "Got Box S"
You should replace it if it is bad. Sometimes you'll see a very little bit of rubbing and then it stops and everything is fine, that one you don't have to replace. But, if it continues, or there is a skip and miss, and there looks like damage, then replace it.

This shouldn't happen, but it tends to sometimes.

Buy a new one, and keep that as an emergency, or go back to your old one and see if the miss goes away.

That's what I do, if I have a part that I KNOW WORKS, because it has in the past, I'll substitute that part and see if it remedies the situation.

See, Jon, now you're already seeing what I meant about these supposedly "NEW" MGB parts that don't exactly work. This happens frequently. That's why everyone has built up a load of spares!

schutnik Avatar
Kelly Leahy
Kenmore, WA (Seattle), USA   usa
1979 MG MGB
Yep, Brian... That's why I've changed from my prior attitude of "replace everything" to my current attitude "replace it only if you can't fix it!". When I first started working on MGBs again, I thought - "everything that's not perfect, just replace it - hell, I've got the money, right? Might as well make it perfect.". After about 1/3 of my "new" parts not working right, I decided - hell with that, time to put the old stuff back on and make it look like "new", but work like "been there forever, rock solid".

Kelly Leahy
Actuarial Software Developer (Milliman, Inc.)
Kenmore, WA (Seattle)
'79 MGB - Leyland White

John D. Weimer Avatar
Cape Girardeau, MO, USA   usa
When you replace the rotor replace the cap at the same time with the same brand. I'd try local parts stores first in an attempt to avoid CCJ parts that don't gee-haw together. That way you can check out where it was made before you buy.

Bill Pilon
Roswell, GA, USA   usa
Check the play in your distributor shaft. There isn't much clearance between the rotor tip and the cap electrode. I've seen a little bit of shaft wobble cause interference.

Jon Zaremba Avatar
Victorville, CA, USA   usa
1979 MG MGB "Brian"
Put the old cap back on and.....BLAMO!.....cruised at 75mph today! No misses...steady exhaust...and a mellow idle...

If everyone keeps selling these junky parts, eventually a manufacturer will have to rise up to provide quality parts for a little more money. I don't mind paying a few extra bucks for a distributor cap that's molded correctly.

So far i've gotten three screwed up parts from Moss.

Jon Zaremba

schutnik Avatar
Kelly Leahy
Kenmore, WA (Seattle), USA   usa
1979 MG MGB

One of the first car stories my Dad ever told me was about a distributor cap that he replaced on an old buick. He said the previous one was cracked, so he had to replace it. He bought one - it was red. He put it on, and he couldn't get the car to run right, no matter what he did. It would run great until the car warmed up, then it would have little power and a very frequent miss. He visually inspected the points, rotor, inside of the cap, checked the plug wires, plugs, etc. No matter what he did, it wouldn't work better. He took a set of wires from another car he had with similiar wire lengths, no difference. Finally, he gave up and asked his best friend's dad - a long time auto tinkerer and all around great mechanic (actually a welder by trade, but big into dune buggys and other VW-based creations).

Mech: what color is the new cap?
Dad: red.
Mech: take that damn thing off and throw it in the trash. Those damn red ones never work! Go back to the store and tell them to sell you a black one!
Dad: huh? what the hell difference can color make?
Mech: all the difference in the world. The stupid plastic they make them out of shrinks and expands with the temp. The black ones don't do that.
Dad: Ok. (goes to store to get a black one).

After an interesting conversation with the store clerk, my dad returns with his new black distributor cap (amazingly, the auto parts store doesn't generally sell buick distributor caps in your choice of color - go figure!). He puts it on, and voila! Everything works beautifully.

That's one of those stories you'll remember till you die - you just can't make that shit up!

Kelly Leahy
Actuarial Software Developer (Milliman, Inc.)
Kenmore, WA (Seattle)
'79 MGB - Leyland White

Jon, I'd still check your distributor shaft for play. Just un-clip the cap and grab the top of the rotor and try to push it back and forth. It only takes a little play to cause irratic engine operation. If its got play, autozone has rebuilts for $60.00. Just dont use the condenser that come with it.

Los Angeles, ca.
1970 M.G. B GT(Elizabeth)
1969 Firebird Convertable(The car with no name-Still not running)

"If I live to be 150, I'd still never finish all the projects I've started"

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