Bad distributor out of the box?

[Mike 71X]

Swapped out my old Proform distributor for a new Proform. Mechanical advance wasn't working on the old one (long story). When I took the old one out I was 10 deg advanced at idle, vacuum disconnected and plugged. I dropped the new one in, rotor in same position, car fires up no problem and idles OK. But when I check idle timing I'm now 5 deg retarded, vacuum disconnected. Is that possible? I put the old one back in and I'm back to 10 deg advanced. I'm going to swap the new one back in to make sure I'm not crazy but ran out of time today. Bad distributor?

 

[Outsider]

Not crazy, or so we will presume. I have found even with factory stock distributors the drive tang varies in relation to the cam lobes. Just put a timing light on it and rotate the initial timing you want and don't worry.

 

[MIKESPOLARA]

I'm kind of surprised that you would expect to hit the timing exactly when changing a distributor by sight/guess

 

[Mike 71X]

Not crazy, or so we will presume. I have found even with factory stock distributors the drive tang varies in relation to the cam lobes. Just put a timing light on it and rotate the initial timing you want and don't worry.

Can't rotate it enough to get to where it should be, the vacuum advance hits the upper rad hose.

 

[Outsider]

Often have rotate the oil pump / dist drive a tooth or two when changing distributors. A big long screw driver or a set of those foot long needle nose pliers work well to twist the gear out to reposition.

I never worry about the drive slot position or the location of the #1 spark plug wire on the cap because of the variances in distributors I have found. I just static time it. Pull #1 spark plug, put finger over spark hole, crank it until its on compression, replace plug, set damper mark/ timing tape to 15 deg before, drop dist in the hole, rotate dist so trigger/pick up are visually aligned, make sure the rotor is in line with #1 plug wire (move wires around cap if necessary), make sure the plug wires are right sequence. This is how I learned in HS auto school 45 years ago, never not had an engine not start right up.

 

[Mike 71X]

Often have rotate the oil pump / dist drive a tooth or two when changing distributors. A big long screw driver or a set of those foot long needle nose pliers work well to twist the gear out to reposition.

I never worry about the drive slot position or the location of the #1 spark plug wire on the cap because of the variances in distributors I have found. I just static time it. Pull #1 spark plug, put finger over spark hole, crank it until its on compression, replace plug, set damper mark/ timing tape to 15 deg before, drop dist in the hole, rotate dist so trigger/pick up are visually aligned, make sure the rotor is in line with #1 plug wire (move wires around cap if necessary), make sure the plug wires are right sequence. This is how I learned in HS auto school 45 years ago, never not had an engine not start right up.

Thank you! Being my first time changing distributor or even timing an engine (should have put that in my original post) I was thinking I needed the wires in exactly the same positions on the cap as before. I think I can turn the distributor back far enough to just move the wires ahead one and not have to mess with the gear. Appreciate it.

 

[HALIFAXHOPS]

Wont hurt a thing clocking the wires. Just the purist guys like show cars really worry about where number one wire is on the cap. Still set the timing afterwards as needed.

 

[AR67GTX]

I’ve encountered the same thing on old Mopar distributors. The tang isn’t always oriented as is commonly referenced.

 

[HALIFAXHOPS]

Believe it or not they are clocked differently from application to application. My theroy is the oil pump dives are installed the same and depending on the acessories on the engine they used anther clocking to clear it like ac on a B/RB. Dual points there are around 8 different RB clocked shafts. Not sure where they clock aftermarked shafts but some proform are definately clocked differently. Nothing in the books at all on that on the single point/elect aluminum distributors, prestolite I have it in the master books.

 

[91r/t]

**** my firecore was about 1-2 cylinders off on the distributor cap compared to where my accel was when I swapped out my distributor for the new firecore. Not a big issue at all just re-clock the gear as necessary like stated. Main thing is hope she runs better with the new distributor.

 

[Mike 71X]

Appreciate the comments, worked like a charm. Moved the accel back and hopped the wires over one. Much better. Pinging is gone and top end seems quieter. Most importantly it's no longer trying to poison me in the garage. Old one was set at 24 advance at idle and was still only 24 all in. Literally would burn your eyes at idle. Great improvement. Starts a little rougher now so I may add a little more to it. Reading 35 all in which gives 9 at idle, assuming the mark is at all close. Should I worry about dialing the vacuum advance back to stay at 35 or is a little north of 35 OK?

 

[Outsider]

I see there has been some input by people a lot smarter than me, such as Halifax, but I will offer what works for my street big block. With the vacuum adv plugged for this check, mine likes about 16 initial and about 16 more mechanical for a total of 32 not taking vac adv into consideration. Seems like all my cars want it in teens for initial.

So hopefully your distributor has an adjustable mech limiter so you can get more initial without too much total for the gas available. To find out how much total adv it will tolerate, I drive mine up a hill at a proper rpm that is in the power band to test for pinging with the combination and adjust until it doesn't ping.

If yours doesn't have the lock screw below the plate to adjust the advance limit, you could buy one of those slotted limiter discs from FBO.

 

[AR67GTX]

That’s pretty much my experience too with my stock 440 in a heavy GTX that is probably carbon’d up some and with pump 93 gas. About 33 total is all it will take without starting to ping. I run a FBO limiter in the dual point so I can run 15 - 16 deg initial.