Distributor question

[D S.]

When the distributor cap is removed I see a condenser and the points and each has a wire attached to them. One wire comes from underneath the plate that the points mount on and attaches to the hold down screw on the vacuum advance. The other black wire that comes from the points goes underneath that plate and feels like it is loose and not connected to anything. Is that right? I can't get either out from underneath the plate. What started this "adventure" was an erratic snapping or popping noise coming from under the distributor cap. At first I thought it was my tachometer cross gear but it is in new condition. The rotor appears okay, the cap isn't cracked and the brass or copper contacts appear undamaged.
I recorded the noise via my I-Phone and a stethoscope device.

[Bill C.]

Re: Distributor question

The wire that screws to the advance plate is a ground.

The other wire is the long wire that comes from the coil. It and the condensor wire are attached to the points.

The long wire passes through a small rubber gromet at the bottom of the distributor. You should be able to move the wire up/down, sliding through the gromet. It does not move far though.

Hope this helps a little....

[Joe L.]

Re: Distributor question

It does not move far though.

Bill and Scott------


The wire does not move far because there is a stop band affixed to the wire on the internal-to-distributor end. This prevents the wire from being pulled out of the distributor for more than an inch or two.

[D S.]

Re: Distributor question

Bill and Joe
I had one of those "Oh, yeah---that's where the wire goes!" moments just after I posted. All the wires are where they are supposed to be. But that irregular popping noise is a stumper. The car runs fine, the tachometer works, but it does die after idling for a while. I guess it's like a mechanic asked me once..."Do you want me to fix a noise or fix a problem?". So, I'm going to drive it until the noise becomes a problem if ever. I can't hear it unless the hood is up.

[Jim T.]

Re: Distributor question

When the distributor cap is removed I see a condenser and the points and each has a wire attached to them. One wire comes from underneath the plate that the points mount on and attaches to the hold down screw on the vacuum advance. The other black wire that comes from the points goes underneath that plate and feels like it is loose and not connected to anything. Is that right? I can't get either out from underneath the plate. What started this "adventure" was an erratic snapping or popping noise coming from under the distributor cap. At first I thought it was my tachometer cross gear but it is in new condition. The rotor appears okay, the cap isn't cracked and the brass or copper contacts appear undamaged.
I recorded the noise via my I-Phone and a stethoscope device.

With only the distributor cap removed and seeing the condenser and points, are you missing the two piece cover over the points and condenser?
With the later uni-set Delco points the two piece cover does not fit and could be missing.
Have you ever removed the distributor and checked the gear drive for clearance between the top of the gear and the distributor housing? My 70's engine would sometime die when leaving the interstate and stopping on the off-ramp. I checked my distributor gear clearance and it was way off, changed it to what my 63-64's shop manual specified, think it was .007, and cured the the engine dieing leaving the interstate.

[D S.]

Re: Distributor question

With only the distributor cap removed and seeing the condenser and points, are you missing the two piece cover over the points and condenser?
With the later uni-set Delco points the two piece cover does not fit and could be missing.
Have you ever removed the distributor and checked the gear drive for clearance between the top of the gear and the distributor housing? My 70's engine would sometime die when leaving the interstate and stopping on the off-ramp. I checked my distributor gear clearance and it was way off, changed it to what my 63-64's shop manual specified, think it was .007, and cured the the engine dieing leaving the interstate.

Jim, I have seen those two piece covers for bids on eBay mostly and wondered what puprpose they served back then and if that same purpose applies to today's parts. So, no, I don't have that cover. Think I should get one?

No, I haven't checked the gear clearance. The first time I noticed it was during the summer when it was god-awful hot here in Texas and the car was running a bit hotter than normal so I figured the dying part was due to heat overload. It only dies after idling for a long period of time. I haven't checked for ill-fitting vacuum hoses yet.

That erratic clicking sound under the distributor cap is what concerns me and may be related to a gear problem somewhere but it sounds like it is just under the distributor cap. It could be coming from internally and the shaft acts as a conductor. I dismantled what I could under the cap but all looks okay there. I changed out the coil wire because it shocked me to touch it but there still is a noise. So, I reassembled everything and said to heck with it.

[Terry M.]

Re: Distributor question

Jim, I have seen those two piece covers for bids on eBay mostly and wondered what puprpose they served back then and if that same purpose applies to today's parts. So, no, I don't have that cover. Think I should get one?

Scott,

Whether you need the two-piece RFI shield depends on how early/late your 1970 is. If you have the full box ignition shielding you don't need it. If on the other hand you have the later 1971 style one-piece distributor shield you should have the RFI shield.

Of course if you have the full box shielding the only harm to having an RFI shield will be to your wallet and the inconvenience of changing the points.

[D S.]

Re: Distributor question

Scott,

Whether you need the two-piece RFI shield depends on how early/late your 1970 is. If you have the full box ignition shielding you don't need it. If on the other hand you have the later 1971 style one-piece distributor shield you should have the RFI shield.

Of course if you have the full box shielding the only harm to having an RFI shield will be to your wallet and the inconvenience of changing the points.

Hey, Terry....great to hear from you.
I have the early 1970 full box cover but fortunately not the small block version with the plugwire side shieldings. Yet, it is still a pain in the rear to remove the lid, the box, the distributor cap, etc. to get the distributor cap off and adjust or work with the points or whatever is close by. So, when I saw the two piece RFI shield (thanks for that) on eBay and on Corvettes I was thinking that I don't another part to contend with under there whether I needed it or not.

[Terry M.]

Re: Distributor question

Hey, Terry....great to hear from you.
I have the early 1970 full box cover but fortunately not the small block version with the plugwire side shieldings. Yet, it is still a pain in the rear to remove the lid, the box, the distributor cap, etc. to get the distributor cap off and adjust or work with the points or whatever is close by. So, when I saw the two piece RFI shield (thanks for that) on eBay and on Corvettes I was thinking that I don't another part to contend with under there whether I needed it or not.

Some of us with the box shielding catch a break in that some of the boxes are two pieces. Held together on the passenger side by two little zinc Philips head screws. Being able to take the box apart helps get it around all the spark plug wires on either a BB or SB. My original is the two piece style.

Don't mess with the RFI shield. You don't need it from a functional standpoint nor from a judging point of view.

[Joe L.]

Re: Distributor question

Hey, Terry....great to hear from you.
I have the early 1970 full box cover but fortunately not the small block version with the plugwire side shieldings. Yet, it is still a pain in the rear to remove the lid, the box, the distributor cap, etc. to get the distributor cap off and adjust or work with the points or whatever is close by. So, when I saw the two piece RFI shield (thanks for that) on eBay and on Corvettes I was thinking that I don't another part to contend with under there whether I needed it or not.

Scott------


Unless the distributor has the breaker plate designed for use with the shield, you won't be able to install it even if you had it. The early 1970 and prior breaker plate, GM #1962141, has no provisions for the shield; the L1970-74 breaker plate, GM #1876641, does.

[Joe L.]

Re: Distributor question

With only the distributor cap removed and seeing the condenser and points, are you missing the two piece cover over the points and condenser?
With the later uni-set Delco points the two piece cover does not fit and could be missing.
Have you ever removed the distributor and checked the gear drive for clearance between the top of the gear and the distributor housing? My 70's engine would sometime die when leaving the interstate and stopping on the off-ramp. I checked my distributor gear clearance and it was way off, changed it to what my 63-64's shop manual specified, think it was .007, and cured the the engine dieing leaving the interstate.

Jim------


I'm amazed that tightening up the distributor shaft end-play corrected the problem you describe. My guess would be that in the process of doing this you unknowingly did something else that was the real thing that brought about correction.

The GM design specification for most of the distributors, except FI, was an end play of 0.025-0.096". EVERY NOS distributor I have measured for end play had a measurement of right at 0.060" which is, curiously, right in the middle of that range.

Personally, I will not set a distributor at an end play of less than 0.025". In fact, I just assembled one for the "ZL-1" and I set it at 0.030". However, I haven't installed it yet and I'm really thinking about changing it to 0.060". But, even at 0.030", I'm still within the GM specification. I won't go outside that spec.; I think they had good reasons for establishing it. As I've said before, if 0.001" (or some such low clearance) was ok, then the designers would have specified the acceptable range as 0.001-0.096 and given themselves even more manufacturing tolerance. But, they didn't; they set the MINIMUM end-play at 0.025".

I think I might know what the reason was, but I don't know it for sure.

[Roger O.]

Re: Distributor question

Personally, I will not set a distributor at an end play of less than 0.025". In fact, I just assembled one for the "ZL-1" and I set it at 0.030". However, I haven't installed it yet and I'm really thinking about changing it to 0.060". But, even at 0.030", I'm still within the GM specification. I won't go outside that spec.; I think they had good reasons for establishing it. As I've said before, if 0.001" (or some such low clearance) was ok, then the designers would have specified the acceptable range as 0.001-0.096 and given themselves even more manufacturing tolerance. But, they didn't; they set the MINIMUM end-play at 0.025".

I think I might know what the reason was, but I don't know it for sure.

Joe,
As you know removing the end play pushes the gear down,dist is permanently longer by around .090 . Do you think its possible the dist housing could be forced up in some cases ?
Roger

[Timothy B.]

Re: Distributor question

I always wondered about this also, every distributor I have picked up has had play like Joe states.

When I replaced the rear main seal on my 63 I checked the shaft of the oil pump to make sure there is up/down play so nothing is tight from shimming the distributor shaft. There visually looks like 3/16 play up/down in the oil pump shaft so I guess everything is OK.

I have a friend that shimmed the distributor shaft on his Olds and ended up damaging the engine. I can't remember exactly what happened but I can find out.

I know the timing will change when the distributor gear moves up and down.

[Jack H.]

Re: Distributor question

The distributor cap internal shielding came about as the result of a Passenger car 'innovation' in 1970. That was the optional in-windshield glass radio antenna...

It appears Corvette (who didn't need this 'feature') adopted it anyway. I suspect the shield inside the distributor allowed a cost reduction via parts elimination/simplification (reduce the distributor shield from a full box to a partial L-shape & delete the discrete RF shields from the SB engine on the front two plug banks; 1+3 and 2+4).

[Duke W.]

Re: Distributor question

The 1963 Corvette Shop manual calls for .002-.007" dist. shaft end play and does not distinguish between FI and non-FI distributors.

GM assembled them to sloopy tolerance because it was cheaper and worked okay with typical low and medium performance engines.

Sloppy end play causes considerable spark scatter, which doesn't help a high output engine.

Achieving maximum output is about assembling the engine and everything associated with it to a set of tight toleraces - tighter than GM used to assemble an average production engine.

Duke