[dataway]

OEM rubber bushing still in place.

[Shiny]

Thanks dataway

Question- does the idle stop end up being the pin/bushing or the weight?

If the pin, how much interference/overtravel for the weight to cam interface?

Mike

[Shiny]

Thanks again to all who helped, I've tamed the weights and hopefully stabilized the idle timing.

Also a big thank-you to Sun Tuned. I reached out as you've suggested and he's able to supply new springs!

I went through the distributor again- cleaned, re-greased, measured, and re-assembled.

I put on what I believe are original weights and springs (will replace again when I get the new ones).

The slot measured 0.390" long and the plate was labeled 726 which I understand means it was designed to allow 26 degrees crank advance. With the heavier springs, it may never get there but I did remove the suspect brass sleeve and made a new one from an aluminum spacer. I squeezed it a little to create a press on the pin and wicked in some loctite. With the slight distortion, the sleeve measured 0.255". At 0.010"/degree, the clearance should now allow 13.5 degrees advance, or 27 at the crank. With my initial set at 9, this will be 36 total, which sounds like a good target.





The combination of heavier springs and the new sleeve have everything working the way I think it should.

dataway - note my cam is different than yours. Mine is stamped "5", yours is "8".

Here's the way it sits now. No wiggling and the weights pull themselves back to home:



Much improved:
Link to Video

I also need to revisit the vacuum advance canister but that's another thread!

Party on, Garth!

Mike

[Cliff R]

For sure the sleeve over the pin needs to be there. It makes contact on both ends of the slot so insures contact with the weights at idle speed and controls the amount of advance when it hits the end of the slot at full advance.

Here I replace the stock rubber sleeve (usually missing or in really poor shape) with a stainless steel sleeve I make in house. Even with a sleeve in place I'll measure the amount of advance and may use the MIG/chainsaw file to shorten up the slot to provide the desired amount of mechanical advance.

The biggest problem I see in this hobby when it comes to distributor tuning and modifications is using springs that are WAY too light in tension and not pulling out ALL the timing at idle speed. Kenth hit on another problem with vacuum advance units not being fully applied when folks are using MVA at idle.

Typically here I use ported vacuum, unless the engine has low compression, lots of overlap, and "weak" signal (vacuum) at idle speed. Trying to use manifold vacuum for those engines often becomes more of a "crutch" than a cure as engines with well thought out components woln't typically want, like, need or respond to a butt-load of timing at idle speed. In any case the debates on that deal rage on today as they have for decades on the Forums. From where I'm sitting if you find yourself having to run the timing WAY off the scale at idle speed to make things happy you simply don't have enough compression for the CID and cam chosen. It's also quite likely that your carburetor is WAY short of supplying enough fuel to your engine via the idle mixture screws, not enough bypass air, or combinations of both.......FWIW.....

I know the pic below is an HEI but a points distributor is done in the same basic fashion......

[Shiny]

Originally Posted by TxSportCoupe

.....it may be a well worn cam gear. Old worn distributor drive gears will cut a cam and the slop is visible with a timing light. A new gear on the bottom of that rebuilt distributor would take up most of the slop. .....k

Revisiting your comment... thanks again!

I think the light springs were the cause of my erratic idle timing but while I'm messing with it...


How much wear is too much? I'd prefer to keep the original gear as I trust the quality and don't need to cause more trouble by fixing something that isn't broken.

BTW, my gear is drilled. Is this for balance or an alignment mark of some kind?





Mike

[Sun Tuned]

That was an optical alignment mark for the factory install.

Not a balance point. But many believe it is. It’s not.

[Shiny]

Originally Posted by Sun Tuned

That was an optical alignment mark for the factory install.

Not a balance point. But many believe it is. It’s not.

Thanks! Folklore is over-rated

[Formulas]

you align that marker with the rotor tip

[dataway]

Shiny, I think you're looking great so far.

The erratic timing on mine ... you could watch the it jump around about five degrees was in the weights/springs and lubrication. I bet yours will be rock solid next time you check it.

[P@blo]

Does anyone have a source for worn advance weight pins for a Pontiac? Not including SunTuned's box of pins

[Sun Tuned]

I’ll die before that box runs out, at the rate I’m using em these days.

You need some?
Can’t take em with me anyhow…

[Shiny]

Originally Posted by dataway

Shiny, I think you're looking great so far.

The erratic timing on mine ... you could watch the it jump around about five degrees was in the weights/springs and lubrication. I bet yours will be rock solid next time you check it.

LOL... I thought it was good to go the last two times I "fixed" it.

Maybe 3rd time's a charm!

I am getting good at asking for help, though, and I appreciate all the time you people spend responding to my endless self-debates.

Mike

[Shiny]

Speaking of pins, there's a lot of clearance between the weights and the springs. If the weights climbed up against the springs, they'd get all balled up.

Is it the rotor that holds them down? I want to make sure there's nothing missing between the weights and the springs.

Mike

[Shiny]

Originally Posted by Shiny

...Also a big thank-you to Sun Tuned. I reached out as you've suggested and he's able to supply new springs!

I put on what I believe are original weights and springs (will replace again when I get the new ones).

These springs I assumed were original are not:




Sun Tuned is a super resource and a genuinely nice guy. He got me set up back to "stock" config which should be a good starting point for me.

FYI the stock springs shown here are 0.028" wire dia, 0.250" OD, 4.5 coils, full loops on the ends. They are definitely stretched at park.

Also, my weights are 0.128" thick, at least the same as stock.

Had Sun Tuned not rescued me, I'm sure I would have achieved the goal of no mechanical advance at idle but would have had way too little at higher rpms.

[Shiny]

Woo hoo!

Thanks to all and especially to Sun Tuned for providing springs.

shaker455 got my carb fixed, set up, and I just now started it up. I'm excited!

The timing is solid while idling for the first time EVER.

Mike

https://1drv.ms/v/s!AiIRc33Ia4jVi5MD...pGyuQ?e=D77b45

[Shiny]

Happiness is stable timing at idle..

https://1drv.ms/v/s!AiIRc33Ia4jVi5ME...07QKw?e=Q1cays

[Dragncar]

Working on a deal to get my own Sun distributor machine. I have a friend who has one in fine working order.
A few things have to fall in place, fingers crossed.

[Dragncar]

Just picked up a NOS Mallory Procomp coil to complete the old school look of my 1962 cast iron, single point MSD-7AL ignition system.
Points TTFMF !

[Shiny]

Here's a point of reference for springs.

Springs supplied by Sun-Tuned (I thank him again) measure:

Wire Dia 0.028
Coil OD 0.250
Coils 4.5
Hooks Full
Hook ID to ID 0.550

When installed, they are stretched at "home" or "weights retracted" position:

ID to ID @ Home 0.700

When weights are extended, the springs are stretched to:

ID to ID Extended 0.780

I started with a bushing that was 0.248" diameter. My original estimate was:

Plate is 726 CW (26 degrees max)
Factory says base should be 9, online suggests up to 12
Measured slot at 0.390
Pin is = 0.185
Clearance in slot is .390-.185 = 0.205
Angular effect is .205/.00986 = 20.8 degrees at distributor, = 41.6 degrees at crank
This is higher than target, so added aluminum bushing to pin. OD of bushing was 0.250 as-received. 0.248 after squeezing for press fit on pin.
New max is .390 - .248 = 0.142/.00986 = 14.4 degrees at distributor or 28.8 at crank, but only if full mechanical is reached.
So total will now be 37.8 degrees mechanical with 9 initial

My base timing ended up being higher than 9 (is 12 for now). The total was therefore quite a bit higher than I wanted but before changing, I thought I'd see if the springs were too stiff to allow full mechanical to kick in. Using my questionable ancient Sears tach and my timing light, here's the curve I measured:



So the springs were not too stiff as the mechanical was close to maxed at ~3000 rpm but was higher than I wanted. This time I increase the bushing diameter to 0.278".

Turns out this got me about where I wanted to be - kicks in at ~900 and maxed at ~2800 so I'm happy for now until I can drive the car:



I suspect I could get away with more max but this should be OK for now.

Mike