I've had three different MSD boxes that ended up failing, so no, they don't last forever. Mounting location and if the box is exposed to engine bay heat also makes a difference.

 

The MSD 6A/AL are very well designed. While it is a design form the late 70's early 80's the components used are first rate. I've had it apart on the bench, looked through the stresses on some of the key parts and I can say they did a really good job.

Heat is the biggest enemy of lifetime. Keep it away from headers, radiators, etc. I put mine under the fender over by the battery. Air comes in around the headlights and keeps the MSD cool.

Running without a coil as a load is another no-no. Under this condition some of the parts see voltages beyond their ratings.

The amount of time it works is dependent on the average temperature that the MSD is kept at, but there are no "short time" (meaning less than 10,000 hrs of operation) parts in the design. No electrolytic capacitors are used (these have less than 10,000 hours of operation at elevated temperatures and decay just by setting on a shelf).

Go here for a great report:
http://www.dainst.com/info/circuits/msd6a_02.pdf

So in answer to you question they should last well beyond 20 years when operated at low temperatures (<100 F).

Ron

 

Low resistance coils will cause them to run hotter, and there is a resistor that will burnout and sometimes take the board out with it.

 

There is no reason to change it. Some last forever and some have troubles early.

 

I've popped my MSD 5 twice; but my 6AL must be a teenager by now.

 

Have the receipt for our 1st MSD-6.

Sept. 1977 --- 85.00 --- Autotronics, Inc.
-----------------------------------------

Bought for our '70 LS6.

Has been on min. of 5-6 vehicles since.

At least 350,000+ miles on it...at least...still going.

Probably most bang-for-buck hi-perf item ever purchased. :thumbsup:

------------------------------------------

Advice:

Keep it as far forward and/or in the air-stream as possible.

Behind the grille is my fave. Large gauge wire! You'll know

when it's in a good spot when you're cleaning bugs off it.


--------------------------------------------

Beginning to switch over to Pertronix these days. --- :beers:

 

I have mine mounted inside the car on the heater box. I agree with the above heat and moisture is the worst enemy. My MSD box was purchased in 1996.

Dave

 

I have a Delta Mark 10 on my car made somewhere around 1970. Still pulls 7500 RPM with plugs gapped at .045". Most, not all, electronics fall into two categories: working or nonworking. Older style CDI's, like the Delta, have triggered SCR's that conduct voltage to the coil. Over time, they may leak, causing weak or no spark. The storage capacitors may also develop leakage. Usually, the capacitors picked for CDI usage are those that have self healing properties should they develop a short or leak.

The interesting CDI's are the ones used on single cylinder cycles. Typically, they have two coils and a diode under the flywheel, and an SCR, capacitor, and resistor in the upper coil. Very simple systems and they work. Advance curve is a function of the magnetic trigger and is "solid state", not mechanical.

 

SCR's should never "leak" electrical current or anything else for that matter in a good circuit like the MSD if the heat is kept down. In fact they should last longer than we will be alive under the proper conditions.

They will degrade and become leaky electrically over time if consistently subjected to a high temperature (>110 degree C, higher than boiling water). The leaking current will cause the capacitor to have a discharge path other than the coil which will degrade performance of the CDI but will not create an out right failure.

Over time this leakage current will cause heat which accelerates the aging process causing more leakage which causes more aging (thermal runaway). The life cuts in half for every 10 degree C increase in temperature as a gross approximation.

The capacitors? These are polyester dielectric in the MSD, made by WIMA in Germany (at least in the ones I have opened). I know of no finer capacitor made in the world. I have never had one fail, even some times when they should have (because I missed an overly stressful operating point that I failed to see in simulation but did see on the bench). I saw them designed into literally millions of power systems and again, 0 failures.

They are self healing (to an extent). Amazing products. Only the shooping (the metal attachment on the end of the capacitor winding) ages and then only in a meaningful time span when subjected to high currents and high temperatures.

Ron

 

It will now that you asked

 

I got that feeling when I hit submit to start this thread, but now I'm officially jinxed!

I'm happily surprised hearing about the high quality-level of the parts used. I wonder if a new 6AL uses the same (or better) quality parts or if it's internals are now assembled with chop sticks.

 

bikeron Quote: Over time this leakage current will cause heat which accelerates the aging process causing more leakage which causes more aging (thermal runaway). The life cuts in half for every 10 degree C increase in temperature as a gross approximation. Unquote.

This is a fact that everyone should be aware of: As mentioned, when you increase the temperature by 10 degrees C, or 18 degrees F, you cut the time for a chemical reaction in half. (Approximately.) As you can see by this, keeping your car in the shade with the windows cracked in the summer will add considerably to the life of the interior. Same with oil temp, antifreeze, rubber hoses, etc. It doesn't take much heat to cut the expected life in half.

Another interesting fact about ball and roller bearings. If you double the load on a ball or roller bearing, you reduce its life by 90%. This is the reason you don't want to use any more spring pressure than necessary on roller lifters. If the cam grinder recommends 180#, don't install at 250# just for good measure. While it is true to err on the high, it's just as bad to err too high.

And as bikeron said, all the internal parts of CDI units I've seen have had first rate parts inside.He mentions WIMA caps: good product. No Jackson capacitors like you find in failed PC's. My Delta used ERO polycarbonate caps, which were high quality German capacitors 40 years ago.

 

I was thinking the same thing the the other day. My 6AL has to be at least 12 years old. I mounted it hidden up under the dash so keeps it out of the heat. I have a MSD timing retard box that connects to it also for the nitrous but I guess they make a 6AL type that does all that in one box now.