Working on my 39 distributor (original style distributor). I have new inner distributor caps from Dennis Carpenter and a new old stock rotor. In the instruction sheet from Carpenter, it says, posts are purposefully tall and would need filing to achieve the correct gap of 0.003 - 0.005" clearance. Initial installation, without any filing, I have approximately 0.015"gap between rotor and posts. How critical is this clearance?
rotor to inner distributor clearance
- Thread starter Tubby
- Start date
Lawson Cox
Well-known member
Just make sure you can turn the rotor all the way around without hitting the terminals on the cap. You should be good to go. I don't think gap is THAT critical.
Lawson Cox
Well-known member
Re: generator and coil 1939 60HP vs 85HP
Are generator and coils the same on 60 and 85 HP engines? Inquiring minds want to know. Thanks
Are generator and coils the same on 60 and 85 HP engines? Inquiring minds want to know. Thanks
Brian
Well-known member
Well, spark plug gap [should be] 0.025", so a .015 gap inside the distributor is nothing! Actually, I recall reading in a service bulletin somewhere, regarding radio noise suppression, and the bulletin says if radio interference is encountered from the distributor, to build up the terminals on those inner caps with solder, and re-assemble the dissy. Turn the rotor by hand, and the brass terminals on the rotor will cut a path through the softer solder. But, it is my opinion that your current .015 gaps are perfectly fine to run. Enjoy!!
Brian
Well-known member
On a different note, but related, understand that an ignition coil, irrespective of its maximum output, will only produce sufficient spark to jump the gap...which is why in your case, it will produce a spark capable of jumping the .025 sparkplug gap whilst under compression, so the .015 gap between rotor and terminal is nothing....So, if you have a problem engine that tends to foul plugs, if you increase the gap between rotor and terminal, to a gap bigger than the plug gap, the coil produces a hotter spark to jump that gap, which can help alleviate the plug fouling.
Bored&Stroked
Well-known member
I'd first make sure the side caps are completely seated - cleaning any crud, corrosion, etc. from the housing. Once you've really cleaned things well and put the caps back in, then measure the gaps.
I prefer gaps that are as close to the minimum as possible - as the larger the gap, the more resistance in the secondary and more chances for the spark to jump someplace you don't like (like through the rotor to the metal that runs through it).
You want as much spark energy as possible making it to the spark plug.
Another area where folks have issues is with running suppressor plug wires (trying to reduce noise) - their resistance can cause a lot of spark issues --> reduced energy at the plug, sparks that jump to ground before the plug, etc.. I try to run solid core wires if at all possible.
I prefer gaps that are as close to the minimum as possible - as the larger the gap, the more resistance in the secondary and more chances for the spark to jump someplace you don't like (like through the rotor to the metal that runs through it).
You want as much spark energy as possible making it to the spark plug.
Another area where folks have issues is with running suppressor plug wires (trying to reduce noise) - their resistance can cause a lot of spark issues --> reduced energy at the plug, sparks that jump to ground before the plug, etc.. I try to run solid core wires if at all possible.
tubman
Well-known member
Here's what I know about rotor to cap contact clearance. Too much can cause a high speed miss. I had the 327/350 engine in my Corvette completely rebuilt. After the usual teething problems and break-in, it ran fine, but would not reach the redline of 6000 RPM. After a bunch of looking around and research, I found out that Delco and all of the other manufacturers were producing a rotor for these engines that had a shorter tip than the originals, a change made universally in the seventies for emissions purposes. I believe the clearance on those replacement rotors exceeded .060". I found a company that made rotors to the original specs and installed one. The engine now will easily rev past 6000 (by how much, I don't want to find out).
I also bought a 250 ft roll of Packard 440.
I also bought a 250 ft roll of Packard 440.
Kube
Super Moderator
Winner, winner, chicken dinner.
38 coupe
Well-known member
I have had to sand down the outside of the last three sets of inner caps to properly fit into the distributors. Once done I had to file down at least one inner cap post on each distributor. I too go for minimal clearance from rotor to post, wear will increase the gap with use.