Big-block timing backing up

I just checked timing on my 440/500. I have an MSD distributor set to bring in all timing by 3,000 rpm, which it does. But if I keep accelerating beyond 4K or so, the timing starts retarding, ultimately by about 7-10 degrees. The timing is steady, not erratic. It advances steadily, then retards steadily with increasing RPM.

I have a collar on the distributor shaft to keep the distributor drive from "walking up". It's a solid roller cam, and I have a bronze gear that's showing some wear. But I can't see how this might solve the problem.

I think I'll now pull out the distributor and try to replicate the issue on the bench with a drill, but thought someone might have seen a similar problem before

Which ignition control box are you using? Does it have a automatic retard option? If so, look there first

I have an MSD Digital 6 Plus. I think it has a timing retard function. I'll check that. Everything else looks good so far.

Thanks!

I don't think it's the retard function of the box. It's a single-stage retard that's not hooked up. Plus, the timing retard I'm observing is a steady thing, not sudden.

How can you tell past 4k rpm that it is retarding?

I set my timing light to my total timing and read directly from the balancer while revving the engine

I checked the backlash of my dizzy drive gear, and it seems like a lot to me. It moves probably 1/4-inch back and forth. I'm thinking maybe that's the problem (worn bronze gear), even though the timing seems to move pretty steadily up, then down, not erratically like I'd normally expect with a worn distributor gear.

Yeah replace that gear first, hope it fixes the problem.

If that doesn’t fix it, I’d put the timing light on another car just to make sure it’s not in the light.

FWIW, the bronze gear lasts about 300 passes on my 493. I don't know what that equates to in street miles. Probably not 10,000??? It gets worn until it's sharp on the edges.

Thanks. I will check my timing light, but I think it's good. The gear isn't sharp on the edges yet, but I can definitely see the wear. I've probably got 50 passes and 100 street miles. Think I might try one of the Crane steel gears that are supposed to be compatible. I'm also starting to think a crank trigger could be a good idea

Step one...... Retest with a timing light that has no dial back type circuits in it.

Ran into this years ago with a motor on the dyno using a dial back light that had never exhibited the issue before.
Tried a non-dial back light...... Problem gone.

Would like to know how we know if the MSD does what it's programmed to do.With programmable timing and a map sensor to take out timing with boost,how can we tell??

I agree with the dial back timing light being suspect. The multi spark goes away real close to where you are seeing a timing change. That multiple spark transition to single spark will confuse the calculation of the strobe.

A crank trigger will fix your issue. I had the same problem with my billet msd dist. on a sb. Installed a crank trigger, problem solved. I now have the same issue with another msd billet dist. In my 511. Timing goes backward about 3 or possibly 4 degrees as rpm is increased. Did not have this issue with the firecore dist. i removed because of a different issue with it . I use a timing light that takes 2 d cell batterys.

Same problem on my 572. On the dyno we saw about 4 degree retard between 6500 and 7500. MSD billet distributor. Since my application was drag only and I ran a 6200 stall converter, we set timing at 6500 on the dyno.

Msd will not acknowledge there is an issue with there distributors. I called them before and after the fix with the crank trigger and still refused to admit there was any issues with the billet distributor. Because i use a Ice Ignition box, im thinking about getting there distributor and new box that has severeral preprogramed electronic timing curves.