Distributor cap to rotor clearance

Rudolph

Rudolph

Senior Member
I have got a few reproduction caps for the crab distributor and a couple bob drake rotors, the rotors collide with the terminals on the cap, made the mistake of trying to run one and busted the rotor and cap, non of them turn freely, tried 3 different distributors.

I understand they use to run basically "0" clearance? I have had to fire the rotors till I can turn the distributor
 
I had that happen and it just knocked the tip of the rotor sideways, which left a pretty big gap to jump between cap and rotor. The car would run but really bad. I could see a decent spark at the plugs when cranking, so I spent a month messing with the carburetors. A new cap and rotor, filed to clear the cap, fixed it, and my carb floats were adjusted to perfection.

It may not have been the quality of the cap, because the rotor spun cleanly before I put the distributor on the car. But then I took the cap off to diddle the rotor into the slot on the cam. I may not have had the cap perfectly seated on the distributor.
 
Mine did the same, just twisted the rotor on its rivet, engine still ran fine tho.

Its definitely 100%something do do with the parts, I have about 10 distributors and swaped caps and rotors, the Bob Drake cap and the no name cap both fouled the NOS rotor and bob drake rotor.

Bob drake rotor needed a grind also, I put microcristlene wax on the distrubtor terminals and filed the rotor till its close as I dare
 
.005 to .015 gap....not all will agree. Something to keep in mind..the rotor must be seated all the way down on the rotor shaft. The shaft hole in the rotor is many times not straight and the rotor will jam and not go all the way. Usually the cap will appear to
be fully engaged on the housing but careful attention will show it is rocking and not seated. Of course the carbon brush is solidly against the unseated rotor.....gotta be careful.
Not to drag this out but some crab caps are designed to use the skinny round gasket
and some are not....gotta watch that too.
Charlie ny
 
Don't file the rotor, that will increase clearance on the terminal of the cap that are not touching, File just the interfering terminal on the cap, it is usually just one terminal.
 
Charlie ny said:
.005 to .015 gap....not all will agree. Something to keep in mind..the rotor must be seated all the way down on the rotor shaft. The shaft hole in the rotor is many times not straight and the rotor will jam and not go all the way. Usually the cap will appear to
be fully engaged on the housing but careful attention will show it is rocking and not seated. Of course the carbon brush is solidly against the unseated rotor.....gotta be careful.
Not to drag this out but some crab caps are designed to use the skinny round gasket
and some are not....gotta watch that too.
Charlie ny
Click to expand...


Interesting. I did not know this. How can you tell if the cap needs a gasket?
 
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