'47 Distibutor Cap Orientation

[Bingster]

Like a dummy, I thought that it made no difference on which side of the distributor cap on my '47 Desoto the snap-on metal clamps were located. When I went to put on the new one,  I noticed a small hole under one of the cap snap-on indentations. Inside of the cap there is also a small built-up area of molded plastic that looks like it has some reason for existing.

So, does the small hole go on the topside clamp or the bottom? 

Also, does it affect the timing if the metal clamps are not completely squared with the indentations on the cap?

 

[Merle Coggins]

The "peg" on the bottom edge of the cap must align with the "notch" in the distributor body to ensure proper alignment of the cap for timing purposes. When all is right the clips should also line up properly.

[Jerry Roberts]

The cap only goes on one way . You will feel when the cap is in the right position . 

[Dodgeb4ya]

Hole to the lower side of distributor. Inside of the cap is the 1" alignment tab ...fit correctly to the distributor housing notch.

[Bingster]

You guys are very patient and kind. I realized when I went back and thought things out that the cap self-locks. Duh! Thanks.

[squirebill]

My story about the hole in the distributor cap.    So in the late '60s I was an 18 year old in my freshman year at college.  I was a "commuter" and took a bus from my home town to the college that was in a city about 20 miles away.  The man who eventually became my step-father had purchased a '50 Plymouth 4 door for $50.00 to use while his primary ride was in the body shop to be repaired from a collision while parked by a drunk driver.  Once he got his car back he offered the Plymouth to me to drive back and forth to school.  I was working under the hood of the car with the engine running and a neighborhood kid about 6 years old was standing on the front bumper asking me about all the things he saw under the hood.  "What's this?"  I'd look at what he was pointing at and say, "That's the radiator."  What's this?"  "That's the generator."  "What's this?"  I looked to see what he was pointing at and it was the distributor.   But as I looked, the distributor cap was kind of dancing around on top of the distributor but the engine was still running.  I turned off the engine and checked out the distributor cap and sure enough both the clips were unclipped and the cap was just kind of sitting on top of the distributor.  I inspected the cap and noticed the sharp edges on the cap were the clips connect were rounded off and figured that was the problem and I needed a new cap. Went to the NAPA store for a new cap and as the guy behind the counter opened the box to show me the new cap he said, "Oh, you got the new design cap....the one with the hole in the side."  I asked him why it had a hole in the side.  He said on these cars fumes from the crankcase can come up past the distributor shaft and collect under the distributor cap.  Then under the right conditions a spark from the points or rotor can ignite the fumes and blow the cap off the distributor.  To stop this from happening a hole was put in the side of the distributor to let this pressure escape.  Thinking back I remembered that on very rare occasions I would hear a "puff' from under the hood when I would start the car but it didn't seem to hurt the running of it so I would go happily on my way.  Guess I was hearing those vapors lighting off and didn't know it.  That's my story.  Regards.     

[Bingster]

That's great!  So there is a reason for that hole.