FI Distributor Question

[George C.]

Re: FI Distributor Question

Wayne,
Thanks for posting the detailed pictures. I have attached a couple of my own from the 365 distributor and I have also just taken the FI 070 distributor apart again, and got the same measurements.

I guess this is not my problem with the dwell readings, maybe it is my meter. Just for something to try I may swap out the breaker plates and see what I get.

Then maybe I will go buy a new dwell meter.

The 1/8 inch movement, up & down I stated was on the point cam plate, which was my mistake, that completely goes away when you install the rotor. My Bad.

Thank you,
George

[William C.]

Re: FI Distributor Question

One other thing to check is the slop where the vacuum advance link is attached to the breaker plate. That wears over time and can easily be brought back into focus with a small hammer (after removing plate from the distributor) the fit should be snug, not bound tightly, but tight enough to eliminate any slop.

[George C.]

Re: FI Distributor Question

One other thing to check is the slop where the vacuum advance link is attached to the breaker plate. That wears over time and can easily be brought back into focus with a small hammer (after removing plate from the distributor) the fit should be snug, not bound tightly, but tight enough to eliminate any slop.

Bill,
Thank you, I checked that too and it is a tight fit. I am starting to believe my meter could be bad.

George

[John D.]

Re: FI Distributor Question

George, Recently I had Don Baker rebuild a NOS 070 FI distributor for me. I can't find the specs that particular 070 in a hurry but here is the specs on a previous NOS 070. Why rebuild a NOS you say.
Bottom Gear end play-Spec. .002/.007 Actual .003
Centrifugal advance/Engine RPM & Dist. Degrees Actual

Start 920/ 0-2.0 920/1.0
Maximum 2350 / 11-13 2350/12.5
Vacuum advance (236-16) Specs
Inches of Hg to Start 3-5 4.5
Inches of Hg-Full Adv 5.75-8.25 8.0
Max Degress advance 7.2-9.2 8.5

Dwell 30 No point float to 6700 (Engine red line is 6200)

Points: NAPA C786P and NAPA condenser

Story: Years ago I was amazed to find out how much play one had until you put the rotor one.
New FI distributor shafts with correct football (not one that fits all) available from Don Baker
John

[George C.]

Re: FI Distributor Question

John,
Good morning and Happy New Year to you. Thank you for the distributor specs, I am at a loss to figure out why I have this declining dwell measurement. There is virtually no lateral play in my breaker plate as evidenced by the measurements in my photo's.

I do have the 236-16 vacuum can, and it appears to work correctly. Either way the declining dwell happens both with the vacuum advance connected and disconnected.
I have ordered a new fancy timing light/dwell meter to be able to better measure what is happening throughout the RPM range. I bought the Equus 5568 Pro-Timing Light.
Thanks for understanding and acknowledging my bad call on the point cam plate play. I really had trouble explaining that one, and then felt a little stupid when I put the rotor back on and the play went away.

George

[Duke W.]

Re: FI Distributor Question

Place a vertical force with your thumb/fingers on the OD of the breaker plate. Does it move significantly? If the plate has the proper snug fit on the dist. housing - one to two thou - there should be virtually no perceptable movement in the above "wobble" test.

Also, what brand/part number points are installed? How old are they? They may be the problem.

A word on terminology. What you refer too as a "cam plate" is officially called "cam w/weight plate". Although my usual preference is to use GM terminology, even though it can sometimes sound arcane, in this case I prefer to call it "cam assembly" since it is a brazed assembly of the cam and weight plate, but using the term "plate" leads to confusion with the breaker plate.

The distributor shaft is called "shaft, main, w/autocam". That "autocam" is what is generally referred to here as the "football", and since refering to is as a "cam" (which it is) can confuse this part with with the "cam w/ weight plate" I endorse the term "football".

Often when discussing individual parts within assemblies, the terminology used to name individual parts can cause confusion as to what specific part is being referenced.

Duke

[Clem Z.]

Re: FI Distributor Question

to stabilize the plate fill a small area under the point area with epoxy and machine it down to the level of the center cast iron support and this will support the plate from the downward pressure caused by the points spring that could change the dwell setting.

[Wayne M.]

Re: FI Distributor Question

.....
A word on terminology. What you refer too as a "cam plate" is officially called "cam w/weight plate". Although my usual preference is to use GM terminology, even though it can sometimes sound arcane, in this case I prefer to call it "cam assembly" since it is a brazed assembly of the cam and weight plate, but using the term "plate" leads to confusion with the breaker plate. ....

Speaking of terminology, the corresponding GM/Delco parts for T.I. (RPO K66) are found in a totally different group # 2.372 than either the points cam w/weight plate (Gr 2.381) or breaker plate (Gr 2.385). The rotating (star wheel) is called "Pole Piece w/weight base", and the stationary (except for vacuum advance movement) plate with magnet is called "Pole Piece w/plate".

[George C.]

Re: FI Distributor Question

Clem,
That is an interesting solution, I will keep it in mind. As an interim solution I installed the breaker plate from my 365 HP distributor and there is much less movement with that plate. Even though the measurements with my calipers are all about the same, it definitely fits tighter, probably due to different wear patterns in each.

The design is a little different but it works. I am still seeing about 3 degrees of decrease in the dwell between idle and about 4,000 RPM. Based on how little that breaker plate moves, I can't believe that plate is causing the problem but don't know what else would cause it.

Tomorrow I will get the recommended NAPA points and see if that changes anything.

Thank you,
George

to stabilize the plate fill a small area under the point area with epoxy and machine it down to the level of the center cast iron support and this will support the plate from the downward pressure caused by the points spring that could change the dwell setting.

[George C.]

Re: FI Distributor Question

Duke,
Please see my response to Clem about changing out the breaker plate.

As for the points, I have tried two sets, one is a Delco Remy set, purchased for the 365 motor, but I can't read the part number. The other set is brand new installed in the FI distributor by the guy who set the advance curve up for me. No name on them that I could find, but definitely higher quality than the Delco Remy and a heavier spring also.

NAPA near me was closed to today, and I got there too late yesterday, but I will pick up a new set tomorrow for comparison testing.

It's a long shot, but my dwell meter is about 40 years old, so I have ordered a new one, see post #20.

After all of my playing around with these distributors I offer up a challenge; does anyone want to put a dwell meter on their car and share the readings at idle and again at 4,000 RPM?

Thank you,
George

[QUOTE=Duke Williams (22045);643687]Place a vertical force with your thumb/fingers on the OD of the breaker plate. Does it move significantly? If the plate has the proper snug fit on the dist. housing - one to two thou - there should be virtually no perceptable movement in the above "wobble" test.

Also, what brand/part number points are installed? How old are they? They may be the problem.