I did a distributor about 25 years ago with welding up the slots but cant remember what side I welded up.. Is it the inside of slot or the outside of slot?? I seen on abodies that there was a thread and it had welded up the inside. By looking at pictures of the FBO plate it looks like that it limits timing by taking up the space on the outside of the slot, Make any sense? LOL Ive got the measurements for welding of the slots/timing. So what are some opinions. Inside slot, outside slot or just getting a FBO plate? THANKS

Outside. In theory it doesn't matter, though if you weld up the inside you have added advance you remove by rotating the distributor. The only issue would be vacuum cannister clearance. Example Cross Ram Manifold. Welding outside would put orientation in stock location and then limit how much mechanical adv.

i bought two of the FBO plates and the stated advance numbers on the plates are far from accurate. welding up an existing plate is a better option.

lewtot184

So I presume you welded your on the outside of slot?

outside

I do the inside to preload the springs more.

If you want the advance fast, do outside, slower do inside

on a side note there was something awhile back & the guy said the center hole on the FBO plate is too big (dont remember the rest of it)

I would weld the inside, the geometry of factory Chrysler distributors is such that the outside of the travel combined with a heavy spring helps get a very slow progressive curve, which is actually what you want (1-2 degrees / 1000 RPM).

If you're going to set it all in at 2000 or 2500 it won't really matter much though. But still will pre-load a super light spring (like the Mr Gasket/Trans Dapt/Mopar springs which are all the same) more to keep you steadier at idle.

And if you do a bad job welding and it falls out you won't end up with too much advance.

Right now these advance slots are setting at .470. This distributor came with the rebuilt engine. I can tell it was cheaply made. Whoever put the distributor together somehow managed to get both roll pins in the reluctor pin holes. LOL Was a pain getting reluctor off. It raises another question as to what hole should the roll pin be located in. the hole that is even with tooth or the hole that is off a little from the tooth. bb engine. My personal engine it is in the offset hole. a buddy of mine has 2 distributors and one is even with tooth and the other offset, Lol

I recently installed the FBO plate,very easy. How accurate? Haven't tested yet. In the past I've also welded them. How accurate is that without a distributor machine? Try doing the math to figure it out. I would say its way more inaccurate to weld. It's trial and error, weld/grind. At least with the plate you can just move it. I'm assuming FBO researched the math before it was made.
Doug

one distributor degree is .0154" of travel. very easy to verify with number drills. the FBO pates I have are using .010" of travel for each distributor degree. so, the numbers on the FBO plates I have don't match up with the mopar stuff. can you still use the plate? sure, just verify with the number drills what the travel is and having a timing tape or degrees marked on the dampner can get you where you need to be. to me the FBO plates are an unnecessary hassle compared with modifying a stock plate.

To limit the mechanical advance mechanism's travel, you weld the end of the slots that the advance arms contact when it advances. I found that chainsaw files are the perfect size to file and shape the slot with after welding. It's a bit of trial and error, but you must use a dial back timing light to see the effects your welding and filing have resulted in.

if the slots are being welded up a person needs to keep in mind that .0154" is one distributor degree. the pin on the centrifugal weight is real close to .25". so, if you want 9 distributor degrees for example all you need is a 9/64" drill bit to fit between the open section of the slot and the centrifugal weight pin. very simple, no special timing lights or anything needed. it's always best to set total timing in a performance application but by simply doing the math initial timing settings will get you pretty close to the desired total. I've been doing this for decades on mopar distributors; it's not rocket science.

Thanks Lew. Your method makes it easy.
Doug

Me too.

While choosing which side to weldup based on spring advance desired maybe a method, isn't just as easy to curve it and if you want preload, bend the spring tab or turn the offset stud on a Prestolite? What if your going from a 15 to an 8, do you really want to preload the spring that much?

I weld up the outside due to that being easier for me to Tig or Mig weld with it held in my vise
I do use both Mr. Gasket 925B springs also

welding the outside of the slot duplicates what the factory did to reduce distributor degrees. truth is either side will work but the curve will be a little slower welding the inside. the FBO plate slots are shortened on the outside.

It's always worth checking the advance curve first!
You can do it on the engine with timing tape.

Measuring the slots will usually give a close idea, but there are other variables.
In general, with 'hot' cam (ie more overlap) and same compression, the engine wants more initial timing. So shortening the inside of the slot compensates for that. Bonus of doing it that way is, the timing will stay in the right range to work with vacuum advance. The real win at the track doing that way is the engine never sees any loss of tiiming in the upper rpms due to slew rate. The extreme example of that is the DC/MP race distributors. (aka 'tach drive')

Here's an illustration of how welding effects the advance.
Its the acceptable timing for a smogged '68 set at the suggested initial. But it could be any distributor with a longer advance than will work with the initial.
The heavy black line shows what happens when the slots are shortened on the inside.
It's drawn at 12.5* because that was the recommended initial timing for non-CAP version of the same engine in 1967.

If the above distributor was on a 'hot' engine, it might be fine that the advance doesn't start until 800 or 900 rpm.

But if that's too late, then slightly reduce the tension of the light spring. That's done by bending the tab or rotating the perch.
With less tension, there will be slightly less force holding the weight and it will move out at lower rpm.