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Discussion Starter #1
I am looking for some advice on what the issue could be that is causing timing fluctuation in my 60 over 460.

Details: This is a drag car set up (71 Mach 1 Mustang)
472 CI
solid roller cam
TFS heads
Super victor intake
1050 dominator (alcohol converted)
MSD 6AL
MSD Blaster coil
MSD billet distributor (Locked out) 34 degrees
Ultra 40 wires (new)

At idle, the timing is pretty solid on the timing mark, however, a we rev the motor slowly to 3000 RPM, the timing will start at 34 then drop to 32 and bounce around between 32 and 35 degrees. I am looking for help on what the issue could be.

Here is what we have changed:
New MSD box
Changed distributors with a new installed bronze gear
New Cap
New Rotor button
new wires
new plugs
removed the MSD starter saver

Here is what we have tested:
2 different timing lights - I verified that 2nd one on my 347 with 35 degrees locked out on MSD distributor idle to 3000 RPM and it is rock solid all the way through.
Completely swapped all of the ignition components as listed above including plugs
Check all of the grounds (motor, MSD, etc...)

Could we have a timing chain that has too much slack and is causing the timing to fluctuate?

The impact of this is a very inconsistent race car. Our last passes at the track 6.44, 6.45, 6.61, 6.55, 6.49.

I am looking for any advice that anyone has or recommendation to check.

Thanks for the Help
 

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How much of a gap is there between the distributor drive gear and the body of the distributor?

If there is much over about .035-.040 or so, the helical cut of the drive gear against the cam might be altering the timing. The shaft inside the distributor is climbing up and down and screwing with your timing.

If so, get some -hardened- shims and shim that space down a bit and see if it helps. Make SURE to allow some gap.

The aluminum distributor body will expand as it heats and you definitely don't want all that seizing up.
 

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I set the distributor up just as MSD recommends. The gear edge to the mounting ring is set to 3.995. MSD range is 3.995" to 4.005" with the end play removed. I will double check the gap and gear edge to mounting ring measurement again for confirmation. Thanks for the reply.
 

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I don't mean that gap. On the bottom of the distributor, between the cast aluminum distributor housing and the drive gear, the gap between them. There is a shim or two so the rotating hard steel gear does not wear the soft aluminum housing. Frequently there is too much gap between them.

I'm assuming you are using a stock style distributor set in the top of the block and driven off the cam, right?

I had a Pontiac back in 1974 that did almost exactly the same thing other than the timing fluctuation was more than yours, along the lines of about 4-6* if I remember correctly. I tried everything: Heavy points thinking the points were floating; light points thinking they were bouncing, disable the vacuum advance, different rotor, tried to stabilize the vacuum advance plate, but none of that worked. I can't remember everything I tried but I fooled around with it for a couple weeks on and off. Until I ran out of patience and it would sit a while until I tried again.

Finally I pulled the distributor and the distance between the drive gear and the distributor housing was about 1/10". I want to say closer to 1/8" but I doubt it was that much. Whatever it was, there was a large gap and I could grab the rotor and move the shaft within the distributor a noticeable amount top to bottom.

Soon as I saw that I realized what was happening, bought some hardened shims from a Pontiac parts specialty company, took the drive gear off, installed the shims to close the gap between the drive gear and the distributor body, and presto, the timing barely moved after that. Use a feeler gauge like setting valve stem to rocker arm clearance to set the gap. Also, if you find a selection of shim thicknesses, use a thicker one between the distributor housing and the rest of them. You don't want to use a thin one here. Same for the last one between the shim stack and the gear, if it turns out you need to use several shims.

The key things are: 1: Use hardened shims, not hardware store washers, and 2: Make sure there is enough space between the drive gear and the distributor body (housing) so that when things heat up and the distributor housing elongates, it does not bind against the gear. If my memory is on task this morning, I seem to remember maybe .030"-.035" or so. It ain't easy being nostalgic with a memory like mine.

Maybe do a search and find out the gap. There are plenty of folks way smarter than I am who know this.

Sorry to beat on those basic points, you probably already know them given your setup, but someone might be reading this who does not know that.

Good luck and let us know what you found.
 

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I set the distributor up just as MSD recommends. The gear edge to the mounting ring is set to 3.995. MSD range is 3.995" to 4.005" with the end play removed. I will double check the gap and gear edge to mounting ring measurement again for confirmation. Thanks for the reply.
This has been discussed here previously. The MSD dimensions are different than the Ford dimensions. Some people have no issues when using the MSD dimensions. Others like you, experience problems. You might want to try using the Ford spec.

 

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Since the timing is locked and it has a msd6, a crank trigger may be the solution for consistent timing.
 
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