SBM Distributor overhaul DIY?

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gzig5

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I'm going through my distributor to clean out 40 years of gunk and install the FBO limit plate and springs. Is there a DIY around here that gives the basics for disassembly, lubrication points and such? I know it's not rocket science but....

How do I decide which springs to install? I have three different wire sizes.
 
gzig5 said:
I'm going through my distributor to clean out 40 years of gunk and install the FBO limit plate and springs. Is there a DIY around here that gives the basics for disassembly, lubrication points and such? I know it's not rocket science but....

How do I decide which springs to install? I have three different wire sizes.
Click to expand...
It may not be rocket science but its three dimensional! :)

If you have it on the engine still I'd measure the timing every few thousand RPM. Then its easy to figure the advance curve in it now.
If its unmolested, FSM specs will at least give a pretty good idea of what it should be.
If yours has a long advance (smog era) follow what I showed Rockable to do here:
360 Tune Up

If you need to shift the starting rpm of the advance or the secondary spring, see here:
Erratic Timing

Changing the springs changes the slope, and the starting point.

For oiling, it varies but most have a felt pad that takes a few drops. I think @halifaxhops has a "how to Article" for that and maybe what else gets a little.
 
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340's, even in '68, had little initial and then a quick primary advance.
Dodge and Plymouth used slightly different numbers but either way give it more initial and shorten the advance.
depending on how its built it will like a little more initial or a bunch. 10 to 12 initial minimum IMO. Start moving around 650 rpm if close to stock.
360 Tune Up
 
Mattax said:
If you have it on the engine still I'd measure the timing every few thousand RPM. Then its easy to figure the advance curve in it now.
If its unmolested, FSM specs will at least give a pretty good idea of what it should be.
Click to expand...

I had done a quicky mapping a few months ago but nothing detailed. I just know that it's all in by 3000. Pic shows how it was setup. Maybe heavy and medium?

The vacuum can has an 11 degree arm and the limiter has 17 stamped in it. So that would be 22 crank degrees with vacuum and 34 mechanical? I had been running no vacuum, 15 initial and it seemed like it topped out at 36 at 3000 but that doesn't make sense if the mechanical limit was 34 unless it wouldn't open all the way.

I'm doing this because the timing bounces a bit at idle and doesn't seem stable . Car doesn't idle well in gear until it is good and hot and will still stall now and then. Going to see if more initial will help.

halifaxhops said:
Lube it first
Click to expand...

Can you elaborate a little bit? I can see areas that looked like they had grease, but what type/weight? Light oil on everything else that slides? Don't want to gum it up so I'd lean towards lighter grease and motor oil but oil tends to sling off and that felt doesnt hold a hell of a lot. There was a pile of crud in the bottom of the housing. Is that the collection area?

It's all cleaned in the ultrasonic tank now and ready to go back together.

IMG_2446[1].JPG
 
gzig5 said:
I'm doing this because the timing bounces a bit at idle and doesn't seem stable . Car doesn't idle well in gear until it is good and hot and will still stall now and then. Going to see if more initial will help.
Click to expand...
Bet more initial will help.
So will delaying the advance.
Turning the primary spring's perch will increase the tension (assuming its not maxed out already)
upload_2019-7-6_17-54-45.png


It's on an eccentric.
upload_2019-1-26_18-55-22-png-png.png


More tension delays the rpm the weights move out.
If it started advancing at 500 rpm, and you were trying to idle at 600 rpm then the timing will vary with small changes in rpm.

The vacuum can has an 11 degree arm and the limiter has 17 stamped in it. So that would be 22 crank degrees with vacuum and 34 mechanical?
Click to expand...
yes
I had been running no vacuum, 15 initial and it seemed like it topped out at 36 at 3000 but that doesn't make sense if the mechanical limit was 34 unless it wouldn't open all the way.
Click to expand...
Two possibilities, and it could be either or both.
* The curve may not have actually topped out at 3000 rpm. The springs may have just slowed it to 1* per 500 rpm or less.
* Timing at idle was 15* but initial timing was less. Direct Connection did that on their race distributors to guarentee easy starting but it makes idle erratic as its very rpm dependent.

To give an idea of how each adjustment works, lets look at a pre-CAP timing curve.
For a perfomance small block we can turn to the 1967 Plymouth 273 4bbl specs.
upload_2019-7-6_18-23-58.png
 
Great info, thanks!
I've got the three spring kit from FBO so I don't think I should need to turn the eccentric, but I have a gauge I may be able to compare the springs with.

I put some light grease on all the sliding surfaces and will lube the felt up. I don't ever remember putting oil in the distributor as part of maintenance but that was 30+ years ago since I actually was tuning an engine so memory may be fuzzy.

One new question if I may..
Should the vacuum advance canister hold a vacuum when I pump it down with the hand pump? Seems to me like it should, but mine doesn't. It starts to move when I get to about 5 lbs but I have to pump like crazy to keep it from going back to the relaxed position.
 
Maybe this will help you visualize the situation you had.
Here's a sketch of what the timing on your engine might have looked like.
upload_2019-7-6_18-46-11.png


A distributor with a curve like this would be typical for an engine where the initial timing was 5*BTC or less!
If this is the case, changing the initial tension isn't really going to help.
Need to shorten the slots.
My preference is to weld the insides of the slots - the reasons why are covered in the thread with Rock able.

You can try the FBO plate. I don't know how well it will work with the angled slots. I assume he's provided enough width. If it has some slots in it that shorten the inside more than the top, that would be best. Then try it with the factory springs first.

If you're never going to run vac advance, then a pretty long primary curve like sketched here will be OK.
If using vac advance, need to let the secondary spring engage at lower rpm.
 
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gzig5 said:
Should the vacuum advance canister hold a vacuum when I pump it down with the hand pump? Seems to me like it should, but mine doesn't. It starts to move when I get to about 5 lbs but I have to pump like crazy to keep it from going back to the relaxed position.
Click to expand...
Should hold better than that.
If/when you're going to use vac advance, I made a 'how to adjust' that's now in the "how to" archives.

gzig5 said:
I've got the three spring kit from FBO so I don't think I should need to turn the eccentric, but I have a gauge I may be able to compare the springs with.
Click to expand...
if you can compare springs with measurements, thats good.
Keep in mind length when its engaged will alter the tension.
I think just shortening the slots should help, but maybe not with the FBO plate. If the plate only limits the advance at high rpm, then you'll have to play with the springs and tension.

Shortening the inside of the slots, automatically puts more tension on the primary spring.
upload_2019-7-6_19-8-8.png


If the only option is limiting the advance,then its a bit more complicated.
With the stock springs the curve will look like this. Arrow represents rotating the distributor to move the whole curve up and get the 15* initial.
upload_2019-7-6_19-16-10.png


So then need to use higher rate springs to get the curve.
upload_2019-7-6_19-17-45.png

That will require some experimentation.
 
Cool! I really appreciate your effort. I'm an engineer and can relate to graphs better then the written word.

Going to give the FBO plate a try. All the cool kids say its the schnizzel. It should help find the combo I like and then I can weld and file. Right now I just want a good, stable idle and reasonable drivability which shouldn't be too hard with the stock-ish 340 cam. I've got some more work to do on the body before I can commit to a serious build on the motor. Then I have to sell a kidney....
Hope to be able to put this in play tomorrow but I need to drive to Appleton and pick up some rear leaf springs.
 
Fired it up late last night with the heavy and medium spring from the FBO kit and the limiter plate on 14. Car definitely liked going from 15 to 20 initial and had to back the idle down quite a bit. Something is goofy though because I'm getting 40 degrees total with no vacuum advance. This is measured with the Inova timing light feature, I don't have any timing tap on the damper. Zero was confirmed with a piston stop. Need to tweak the carb and check a couple other things but it's almost like the plate isn't working. I added five initial with a lower mechanical limit and got five more total. I'll map it out and then pull it back out and try another slot with no other changes. One of the original springs hit the floor and disappeared so that complicates changing one thing at a time.
 
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