I've read threads about using MSD boxes; the pluses, the minuses. This got me to thinking. What is the expected life span of an MSD 6a? Do they give an indication they're going out? Mine was installed in Apr., '99; has 20,500 miles on it. The box has worked flawlessly. I've read threads that claim MSD boxes 10-15 years old still working. Others, several thousand miles, goes kaput. BTW, I keep the factory ignition set-up in a waterproof bag in the trunk.
Timing Marks
I've always tried to set my timing (440) with a timing light but the timing marks (marked with bright nail polish) did not appear on the damper. So, just to satisfy my curiosity, I connected the timing light to #2, and there was the timing mark on the damper. Does the distributor need to be moved back (?) a tooth? Does it really matter what cylinder you use to set your timing?
Thanks,
Ferd

I've had mixed luck with the boxes. As to timing, you can use #1, #6, assuming GM or Chrysler, or the coil wire.

Not all timing lights work with MSD ignitions. You need to verify #1 tcd and your marks. You time off of #1.

The MSD box (6T) on my street car was given to me used in 1991. It's still going. If your timing light flashes on #2 it should also flash on #1. The timing light doesn't know what cylinder it's connected to. It wont flash at the correct spot on the dampner if its on the wrong cylinder. If your motor runs half decent, it is not a tooth off. do not connect to the coil wire. It will flash to often, 4 times per crank revolution. The distributor turns 1/2 crank speed.
Doug

The timing light I purchased several years ago was made to handle MSD boxes. Has a steady flash to it. Engine runs great; I 've set timing using the vacuum method.

You need to check timing vacuum advance unplugged, idle low like 700 rpm with no mechanical advance . You should be able to see the marks. If you can not pull number one plug and get it at tdc compression stroke and see where your marks are.

Setting the initial timing with a vacuum gauge at idle speed is fine, you also need to check the total timing in the upper RPM range above where the mechanical advance is advanced all the way in
Total timing determines how much power the motor will make at WOT above where the distributor advance is in all the way
To much total timing will hurt the motor , to little will make less power than the motor could make if timed for max power
Make sure to verify the TDC marks on your balancer and timing cover tab by removing #1 spark plug and have someone bump the starter over a little at a time while you hold a finger over the spark plug hole to hear that piston start coming up on compression, if it blows your finger off the hole do it again until the pstons is still coming up and then have some one use a breaker bar and socket on the crank bolt to rotate it clockwise slowly while you use a thin bladed screw driver or some other tool you have to push on the piston top to feel it come up all the way and stop and then start to go back down, rock it back in forth until you get it to stop at TDC and then look at your balancer and timing tab to see if they are aligned or not
If it is good figure out why your timing light is not showing you the correct timing, if it is off, fix it
I have a 1968 440 HP1 motor in my shop now that someone else had work on for this customer, they added a 8:71 BDS blower, late model (1971 and later) forged Speed Pro flat top pistons with no valve relief pistons to lower the compression ratio, a real small solid roller lifter cam(less than .500 net valve lift) and a pre 1966 (1962 to 1965 only) timing cover with the flat timing tab. It has a solid steel blower hub on it with no dampener, it does have a timing tape glued onto the hub but I didn't verify the TDC on this motor yet, I will later
It has a early MSD distributor with a MSD 6 ignition box and no timing boost retard module for retarding the timing under boost, it will get that also
Always verify TDC, ALWAYS when their are problems, due the basics first

Can’t use a dial back with an MSD

stock balancer,outerring moving?they will come apart!

stock balancer? they will come apart ,the outer ring will spin .

had one earlier this year on a BB ford. it had been to a couple of different shops. They all reset the timing LOL. Every time you'd snap the throttle, the outer ring would move about 10 degrees LOL

Engine has a fluid damper.

You still need to verify TDC and the balancer 0 lining up to the timing cover tab 0.