FI Distributor Question

[George C.]

Hi Guys,
I am working on my 65 365 HP car and have installed a restored 380 FI unit. I have a problem with the distributor, it is an 070 unit. The problem is the dwell decreases by 6-8 degrees when I rev the engine to 2500 3000 RPM.

Although the total end play is in spec, the plate assembly with the cam that opens the points moves up and down a little more than 1/8 of an inch.

I can't find a diagram anywhere and have searched the archives with no success. I also see in the archives that printed material for this distributor seems scarce.

Can someone tell me if this is normal, or am I missing a spacer somewhere, maybe above or below the cam plate?

Thank you in advance,
George

[George C.]

Re: FI Distributor Question

Guys,
I might have been too quick to decide this is a problem, with the rotor installed that cam plate doesn't move as previously reported. Still curious why the dwell changes with RPM, as the bushings in the housing seem tight and free of any side to side movement.

All ideas of what to check and how are welcome.

George

[William C.]

Re: FI Distributor Question

How much dwell change, and how are you checking it?

[Edward J.]

Re: FI Distributor Question

George, the cam plate rides on the upper bearing in the dist. sometimes if this plate or the bronze bushing is worn the plate will wobble, causing the dwell to move around a little. This upper bushing can be tight around the shaft with no movement but the plate does rotates when the vacuum advance moves. I am not a fuel injection expert so I not even sure your car a vacuum can that is working. Duke just recently wrote a article Blue Printing a Dist. and posted on the TSB. might be worth reading.

[George C.]

Re: FI Distributor Question

Bill,
Hi, I am checking it with a dwell meter, at idle I have it set for 30 degrees and it drops with high revs, about 25 degrees at 3,000. Not fluctuating just a slow and steady decline.
Thank you,
George

[George C.]

Re: FI Distributor Question

Ed,
Hi, I have read dukes posting and all other info I could find in the TSB. The shaft bushing appear tight, I should pull it apart again and check the plate to see if it is sloppy on the shaft. Don't know if there are any parts to change there except maybe the cam plate itself.
Thank you,
George

George, the cam plate rides on the upper bearing in the dist. sometimes if this plate or the bronze bushing is worn the plate will wobble, causing the dwell to move around a little. This upper bushing can be tight around the shaft with no movement but the plate does rotates when the vacuum advance moves. I am not a fuel injection expert so I not even sure your car a vacuum can that is working. Duke just recently wrote a article Blue Printing a Dist. and posted on the TSB. might be worth reading.

[Duke W.]

Re: FI Distributor Question

A drop off in dwell with revs is indicative of a sloppy breaker plate. It should fit snug on the housing with virtually no perceptible side play and should not deflect if you try to push it down at the edge, and there should be little plate end play. The 1/8" you stated is way too much. The wavy spring washer that secures the plate to the housing should keep minor end play in check.

The replacement spring clip that Jim got for his L-79 distributor was not "wavy", so we reused the original... same applied to the replacement seal. It was just a generic flat nylon washer- no where near like the original design, so we also reused the original, but the new felt washer was the same as the old, so we used the new one after wetting it with oil.

Duke

[Mike Z.]

Re: FI Distributor Question

The dwell should not vary more than one or two degrees from idle though the full RPM range-at least that is what I see of freshly rebuild units I test on my Sun machine. Any larger variance is due to wear: point tension spring (try HD points), cam piece, or upper bushing/point plate (there should be very little movement here-it is supposed to rotate, not vary up/down or sideways). The fact it is an FI unit has no bearing on the problem you describe, the upper portion of the unit is essentially the same as a non-FI unit.
Good luck,
Mike

[George C.]

Re: FI Distributor Question

A drop off in dwell with revs is indicative of a sloppy breaker plate. It should fit snug on the housing with virtually no perceptible side play and should not deflect if you try to push it down at the edge, and there should be little plate end play. The 1/8" you stated is way too much. The wavy spring washer that secures the plate to the housing should keep minor end play in check.

The replacement spring clip that Jim got for his L-79 distributor was not "wavy", so we reused the original... same applied to the replacement seal. It was just a generic flat nylon washer- no where near like the original design, so we also reused the original, but the new felt washer was the same as the old, so we used the new one after wetting it with oil.

Duke

Duke,
My original post was not clear, the breaker plate is not moving. What I thought was moving up & down is the cam plate, but I later posted a correction, it only moves up and down with the rotor off. Once the rotor is installed it doesn't move. I re-tested it this afternoon and I am losing 4 degrees from idle at 1,000 to 4,500 RPM. Starts at 29 and ends at 25. I am hoping the problem maybe the points, and will go get the NAPA
CS7860 you suggested in the article you wrote.
But I will pull it out and check for the wavy washer and side play in the cam plate.
George

[George C.]

Re: FI Distributor Question

Mike,
Thanks I am going to replace the points tomorrow and probably disassemble the distributor again to look for worn parts.
George

[George C.]

Re: FI Distributor Question

Hi to everyone who has posted. I pulled the distributor out and disassembled it Once I had it out and on the bench there is some play in the breaker plate.

I found that it has the flat spring clip holding the breaker plate down, not the wavy one discussed in multiple TSB threads. So I pulled my 365 HP distributor apart, and it has the wavy spring washer, I "borrowed" it and put it on the FI distributor but the plate still moves a little bit. I will try it tomorrow and see how much things have changed.

If the breaker plate is still moving enough to affect the dwell, where should I expect the wear to be, is it in the plate bushing ID or the OD of the bushing surface on the housing?

Thank you all again,
George

[Duke W.]

Re: FI Distributor Question

The wear is probably the bushing in the plate. It fits over a precision machined OD on the dist. housing. Unfortunately I'm not aware that new breaker plates are available from any source. I'm sure Joe L. has some (not for sale), and Clup said he has some good used ones, so you might give him a buzz. Mic the ODs of both distributors. If they are within a thou or two the distributor housings are probably not worn.

Also, a good machinist could probably make a new bushing if you can't find a serviceable example.

A wobbly breaker plate that probably was out of spec when new often kept my 340 HP engine from revving to the redline, but that probably saved the engine because I found a badly cracked connecting rod at 115K miles when I tore it down for inspection and rebuild.

Prior to that I had figured out how to make the single point distributor work to 7K revs by doing the blueprint/overhaul I described in the prior thread. That was decades ago, so I was able to buy a new breaker plate from GM. That along with shimming up end play to the 2 to 7 thou spec and the 32 oz. points allowed it to work every bit as well as the TI that I ran for awhile, but without the sudden, no notice failures.

Properly set up the single point distributor works very well and has no "black box" to suddenly leave you stranded. The problem all along was the sloppy way the distributors were assembled. They worked okay on low to medium performance engine that rarely went over 5K revs, but as assembled from the plant, they were marginal on high revving SHP/FI engines.

Like I often say: It's all in the details!

Duke

[Wayne M.]

Re: FI Distributor Question

George --- just checked the ID of the NOS plate bushing shown below (big pic), and it's 0.644". The brass upper bushing OD (thumbnail below) is 0.643-642", so a very close tolerance between the two. On a used '66 distrib that I have on the bench, I checked the plate "wobble" and I'd guess at about 1 or 2 thou at the edge, without the vac advance arm attached (which should steady it a little more) Nowhere near the 1/8" you originally reported.



n

[Duke W.]

Re: FI Distributor Question

You need to measure the OD of the upper machined surface of the dist. housing that encircles the breaker plate bushing. The thumbnail that you quote the OD measurment looks like the advance limit pin.

The clearance between the breaker plate bushing and the dist. housing should be snug - one to two thou.

Duke

[Wayne M.]

Re: FI Distributor Question

You need to measure the OD of the upper machined surface of the dist. housing that encircles the breaker plate bushing. The thumbnail that you quote the OD measurment looks like the advance limit pin. ...

Duke -- here's another shot with a little more scale reference. OD of this bushing is 0.643" (where the breaker plate bushing rides).

That previous upper bushing was removed from one of my distrib's eons ago; can't even remember why.