250GT Distributor Caps

Moderators: 330GT, abrent

enio45
Posts: 826
Joined: Wed Jul 02, 2003 6:56 pm
Location: Gilbert, AZ

Re: 250GT Distributor Caps

Post by enio45 »

John, are u talking about the capacitor on each distributor??

If so - i send them out and have had them replated clear zinc - - as matter of fact - i just sent out 4 yesterday for plating.

Because they are sealed - you can replate them with no damage done.

The orig ones have the 2 mounting tabs on them if i am correct?
Ed Montini
330 GT 2+2 Series II - 8289
58 Ellena - 0855GT - orig drivetrain
87 El Camino SS
John Vardanian
Posts: 1906
Joined: Wed Sep 04, 2002 12:13 am
Location: San Francisco Area

Re: 250GT Distributor Caps

Post by John Vardanian »

Thanks Ed. Did you get them back from the plater and they look undamaged?

john
PF Coupe
enio45
Posts: 826
Joined: Wed Jul 02, 2003 6:56 pm
Location: Gilbert, AZ

Re: 250GT Distributor Caps

Post by enio45 »

They will be back in a week or so - i used Detail Plating in Sanger California - - he is our plater of choice for zinc, gold and phosphate - -previously i never had any damage to others i sent out...ill send pics when they are back.....and if u send them out, send nuts and screws for the mounting and the brackets - coil bracket and resistor bracket - i have seen them in zinc and cad - -
Ed Montini
330 GT 2+2 Series II - 8289
58 Ellena - 0855GT - orig drivetrain
87 El Camino SS
John Vardanian
Posts: 1906
Joined: Wed Sep 04, 2002 12:13 am
Location: San Francisco Area

Re: 250GT Distributor Caps

Post by John Vardanian »

Thanks Ed, email me some pics when you get them back. Thanks.

john
PF Coupe
User avatar
peterp
Posts: 314
Joined: Sun Feb 12, 2006 9:42 am
Location: NJ

Re: 250GT Distributor Caps

Post by peterp »

Photo of one of my distributor caps -- definitely more brown than black, though they can look quite dark depending on lighting. I put new number stickers in (not pictured) and I kind of regret it because the brightish white looks a little out of place. Should the distributor caps have a gasket? I don't think mine do, but can't be positive from memory.

Image

Below are some photos of an original and repro rotor. The repro has a much narrower and shorter tip. It seems like the tip width differences might affect timing by a degree or two. I didn't like having a repro, so I replaced it with an original, but couldn't tell a difference in driving performance.

Image

Image
Peter P
1966 330 2+2 series 2 #8169
John Vardanian
Posts: 1906
Joined: Wed Sep 04, 2002 12:13 am
Location: San Francisco Area

Re: 250GT Distributor Caps

Post by John Vardanian »

Thanks Peter, it looks like the spark gaps would be different between the two types of rotors. Wouldn't his affect the dwell?

john
PF Coupe
User avatar
tyang
Posts: 4060
Joined: Wed Nov 27, 2002 10:28 pm
Location: New York
Contact:

Re: 250GT Distributor Caps

Post by tyang »

Hi John,

The event duration of the spark should be shorter than the width of the rotor tip. The trick is to make sure the points plate is set up so the event lands on the center of each cylinder as the rotor comes around.

I re-read that to make sure it made sense, and yet it barely sounds like English! Maybe someone else can describe it better!

Tom
'63 330 America #5053
User avatar
peterp
Posts: 314
Joined: Sun Feb 12, 2006 9:42 am
Location: NJ

Re: 250GT Distributor Caps

Post by peterp »

John Vardanian wrote:Thanks Peter, it looks like the spark gaps would be different between the two types of rotors. Wouldn't his affect the dwell?

john
John, I didn't measure them with calipers, but it looked like the distance from the rotor center to the end of the electrode was the same for both. The aftermarket rotor has a longer plastic housing to make up for the shorter electrode tip, so the total length is about the same. I don't what the difference is functionally for a wider electrode vs narrow -- I had only thought about the potential timing difference, but your question makes me curious what other effects might result from a wider tip.
Peter P
1966 330 2+2 series 2 #8169
John Vardanian
Posts: 1906
Joined: Wed Sep 04, 2002 12:13 am
Location: San Francisco Area

Re: 250GT Distributor Caps

Post by John Vardanian »

PF Coupe
afwrench
Posts: 412
Joined: Fri Jan 28, 2005 9:13 am
Location: upstate new york

Re: 250GT Distributor Caps

Post by afwrench »

Hi John, since Tom Y mentioned it I think that he means that an idealized situation would have the centerline of the rotor electrode dead center on the terminal of the cap at the spark event. I ask Tom to scold me if I have not added any clarity.As far as dwell goes ,that is the # of degrees of shaft rotation that the points remain closed.It is a direct result of the point gap and is the time that the coil has to "recharge" prior to the next spark. Dwell can influence timing but timing does not influence dwell. Set the points then set the timing.Hope I am right as I am having more "senior" moments both in and out of the garage. Best regards, Mike
72,365gtc4,14681,2007 599 GTB
John Vardanian
Posts: 1906
Joined: Wed Sep 04, 2002 12:13 am
Location: San Francisco Area

Re: 250GT Distributor Caps

Post by John Vardanian »

Thanks AFWrench. So, the lower the dwell, the larger the points gap, and the larger the points gap the more time the coil has to recharge. Is this right?

john
PF Coupe
DWR46
Posts: 621
Joined: Tue Sep 22, 2009 8:23 pm

Re: 250GT Distributor Caps

Post by DWR46 »

John: Dwell goes up as point gaps go down. Larger amounts of dwell give the coil more time to recharge. However, larger point gaps make starting easier. It is all a "balance". That is why the American manufacturers in the 1960s went to dual point systems and wired the points as "dwell extenders". They were having trouble getting good spark (coil saturation) at the higher revs the muscle car engines were attaining, so they needed more dwell and a dual point set up achieved this. Do not confuse this with the Ferrari method of using each set of points to fire three cylinders, the Americans used one set of points to open the circuit and one set to close the circuit.
John Vardanian
Posts: 1906
Joined: Wed Sep 04, 2002 12:13 am
Location: San Francisco Area

Re: 250GT Distributor Caps

Post by John Vardanian »

Thanks Dyke for that explanation, so for the performance tuned motor the dwell is greater then, correct?
Can we talk about plug gaps? How do the plug gaps correlate to engine performance. Experimenting a little bit, I noticed that larger gaps give bigger spark, but how big can you get with the gaps before it starts defeating the purpose?

john
PF Coupe
DWR46
Posts: 621
Joined: Tue Sep 22, 2009 8:23 pm

Re: 250GT Distributor Caps

Post by DWR46 »

John: The more dwell, the stronger spark. That is why Ferrari used two sets of points and a three lobe cam for the V-12's. The fewer cam lobes, the more dwell you get (the coil has more time to recharge between calls for sparks). The closer the plug gap, the easier it is for the spark to jump the gap. However, narrow plug gaps don't make a very "fat" spark and result in more difficult starting. A wide plug gap eases starting, but makes it more difficult for the spark to jump the gap under high load (pressure) cylinder conditions. That is why low performance, low reving engines generally had wide plug gaps, and high performance, high reving engines used smaller plug gaps. Electronic and CD ignition changed all this and now cars have enough ignition energy to jump wide gaps at high load conditions.
B24Spider
Posts: 23
Joined: Wed Mar 02, 2011 3:10 pm

Re: 250GT Distributor Caps

Post by B24Spider »

A minor comment re polishing distributor caps; keep in mind that rouge is made with iron oxide. While John was very careful to thoroughly wash his afterwards, failure to remove all the polishing compound could lead to arcing/tracking and resultant misfires.
-Steve
Post Reply