Vacuum Advance

[threewood]

Ok I spent more time trying figuring this out. It is clearly only getting about 10 degrees of advance with the Pertronix III, and it was clear (based on me rereading my build thread) that with the points I was getting more like 20. I have this nasty feeling that the magnetic fields that the Pertronix III use to fire the coil against the points cam are not sharp enough and get smeared out. The real electronic ignition reluctor is sharp gear teeth not the soft bumps for the points.

Been thinking about this. An easy way to check how much vacuum advance you have is to idle the motor and then idle it while using a hand pump to actuate the vacuum canister. Checking the timing both with and without will show you how much is available and at what in/hg. You would almost need to route a vacuum gauge to the windshield and drive it to see how much you are actually seeing while driving.

 

[JimKueneman]

Been thinking about this. An easy way to check how much vacuum advance you have is to idle the motor and then idle it while using a hand pump to actuate the vacuum canister. Checking the timing both with and without will show you how much is available and at what in/hg. You would almost need to route a vacuum gauge to the windshield and drive it to see how much you are actually seeing while driving.

That would work if the guy at O'Reilly's would sell me a vacuum pump. He said they were junk and would not sell it to me

 

[threewood]

That would work if the guy at O'Reilly's would sell me a vacuum pump. He said they were junk and would not sell it to me

I have a cheap Amazon pump on the way ( $20.00 ). It works great as long as it doesn't ingest brake fluid, like my last one did. https://www.amazon.com/gp/product/B00T3W3FB2/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

[JimKueneman]

I have a cheap Amazon pump on the way ( $20.00 ). It works great as long as it doesn't ingest brake fluid, like my last one did. https://www.amazon.com/gp/product/B00T3W3FB2/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

I saw those. They look like knock offs of 30 year old Snap-On pump that does not work I have!

 

[threewood]

I saw those. They look like knock offs of 30 year old Snap-On pump that does not work I have!

This is my second one lol. First one worked very good before I broke it I consider it a consumable.

 

[Nacho-RT74]

well I remember have read clearly LBS and not X on the arms I have had in hands... If I find some will post

( editing... or it was just L ? )

 

[91r/t]

And if you do the math with a 2 degree ATDC initial + (19*2) = 36 BTDC total mechanical + (9.5*2) = 55 BTDC total. Just about right, maybe a bit more than ideal

Jim

That's where the adjustable canister that the aftermarket distributors have are awesome. I dialed mine in right dead nuts to add exactly what I needed.

 

[69Bee]

Awesome! Thats what I thought. There is also an L or R on some of them to tell which way they mount in the distributor depending on its rotation I believe .

Yes, the L & R is for the rotation of the distributor. One is used for small blocks and the other big blocks.

 

[Nacho-RT74]

got it!!!! so I was wrong then!!! thanks!!! new stuff to learn!

mine is Big block so I guess L is the correct and that's why I allways see the L on the replacements

 

[HALIFAXHOPS]

Just FYI on the b/rb advances there are two different shaped arms make sure you order the one you need, and no they can be points or elect.

 

[JimKueneman]

@Billccm traded me a vacuum pump for my coolant pressure tester. Bottom line is the Pertronix III cheap cheesy mechanical design has worn in just a few weeks of driving such that the plate that the vacuum advance pulls is loose and floppy allowing some of the normal pull action to be translated into a rocking movement in the plate and not rotational. Trying to think of a way to get the parts clamped together better at the pivot point and remove the slop in a long lasting way. I am thinking of another job for Shapeways and 3D Printing. It is a simple piece I think I can make to snap in and glue to make the unit way more robust.
On the verge of putting the perfectly functional points back in.

 

[HALIFAXHOPS]

@Billccm traded me a vacuum pump for my coolant pressure tester. Bottom line is the Pertronix III cheap cheesy mechanical design has worn in just a few weeks of driving such that the plate that the vacuum advance pulls is loose and floppy allowing some of the normal pull action to be translated into a rocking movement in the plate and not rotational. Trying to think of a way to get the parts clamped together better at the pivot point and remove the slop in a long lasting way. I am thinking of another job for Shapeways and 3D Printing. It is a simple piece I think I can make to snap in and glue to make the unit way more robust.
On the verge of putting the perfectly functional points back in.

The triangle clip worn out on the bottom of the plate? They do crack and lose tension.

 

[JimKueneman]

The triangle clip worn out on the bottom of the plate? They do crack and lose tension.

Yea that plastic "bushing" that is mounted to the upper plate (by melting 3 pins) then has the 3 small clips that clip into the lower plate. They are worn and allow the upper to rock on the lower already.

 

[HALIFAXHOPS]

I am lost thinking the bushing that goes under the cam plate got a pic by chance? I rebuild them and never saw 3 small clips .

 

[HALIFAXHOPS]

Like this?

 

[HALIFAXHOPS]

If you need a plate I have a bunch just need a pic of what you have now.

 

[JimKueneman]

Sorry I’m bitching about the Pertronix III design. The factory points are a solid mechanical design!

 

[HALIFAXHOPS]

Usually the petronix works well, but points are a nice sold design that worked well for many years. Call petronix tell them what happened they stand up to there products, hell a friend @MoparMitch had one fail that he had for a long while before putting it in and I believe they sent him a new unit.

 

[HALIFAXHOPS]

OK now I got what happened. Was thinking a stock unit.

 

[JimKueneman]

Usually the petronix works well, but points are a nice sold design that worked well for many years. Call petronix tell them what happened they stand up to there products, hell a friend @MoparMitch had one fail that he had for a long while before putting it in and I believe they sent him a new unit.

Really? The III version? I find that pot metal and plastic plate and rotator design about as cheap and flimsily as it could possibly be. They do stand behind it as I have 2 more of the plates they sent me but if I have to replace them every few thousand miles because the plastic wears out to the point the vacuum advance does not function correctly I may as well have points.