[Ram Air IV]

I have an original 78 Transam, with the 400 Pontiac engine and every since I have owned this car, it always arcs a pinhole thru the rotor cap,replaced with new factory and MSD caps ,usually good for a few miles then arc thru occurs upon restart. Just want to change the distributor out to something more dependable. Any good luck with the aftermarket ones? Thanks...

[MNBob]

Mine is a one owner and the HEI has always worked well. I can't remember the first time I put in a MSD ignition, but you remove the module when you do. I have always used Accel caps.

Where is the pinhole in the cap, on the top? The caps don't seat all that easily, you need to make sure it is all the way down and in the notches.

[Ram Air IV]

I will try the Accel rotor and the pinhole burn thru is on top of the cap everytime.I also installed the MSD coil and replaced the module with a brand new factory GM one . Thanks...

[MNBob]

I think the MSD coil is remote and they use a cap cover. Maybe there is something wrong with this setup. The first thing I would try is a new cap and rotor and the stock in-cap coil and see if it still does it.

I use an Accel in-cap coil. It uses the little button rotor contactor, with the spring, rubber washer, and dielectric grease like the factory coil.

[Ram Air IV]

The MSD coil is the in-cap design and the dielectric grease was applied on the rubber washer ,that fits in the center of the cap. List of "new" items is GM cap,plug wires & module , Accel rotor,Borg Warner pick-up coil . Thanks Bob

[Skip Fix]

I've always used Accel cap and rotor and in cap coil. They a;so have a special coil "button" that is supposed to handle more jiuce than a factory "button".

[Ben M.]

What's the plug gap set at? Too high (0.060 or more) will cause what you are describing. I tend to gap my HEI plugs to 0.045-0.050" and no more.

[Ram Air IV]

I will re-gap the plugs @ (.045-.050 ) and give that a try. I have always gapped the plugs @ (.060 )according to GM specs. Always thought that gap was extremely wide for the R-45 TSX and was sceptical about where the high voltage was going bleed off too.Great idea ,Ben

[MNBob]

Something is wrong, it shouldn't be doing this. I thought about excessive shaft endplay, but I really don't think it could cause this problem.

This might be one of those issues, where you have to mix and match parts until you find which one is causing the issue. I know it sounds crude, but I can't think of any other way.

[MNBob]

Just saw the previous post, with the MSD 6A, I always gap at .060. Still, maybe that does not work with the MSD coil.

[gtohurstjudge]

Constant burning thru the rotor on an HEI ignition is generally caused by just
one thing.....a gap between the carbon button in the top of the cap and the metal tang
in the middle of the rotor. Try putting a dab of grease on the metal tang and stick the cap back on, then remove and see if the grease got on the carbon tip. If not, bend the tang up on the rotor until it makes firm contact. The rotor tang acts like a spring and is easily bendable
upward to solve the gap problem. When there is a gap the hot spark on the HEI acts like an arc welder on the distributor rotor. Also, make sure the spring between the bottom of the coil and the carbon tab is pushing the tab as far down as it can travel. If not stretch out the spring until it does.

[highway star]

Originally Posted by Ram Air IV

I have an original 78 Transam, with the 400 Pontiac engine and every since I have owned this car, it always arcs a pinhole thru the rotor cap,replaced with new factory and MSD caps ,usually good for a few miles then arc thru occurs upon restart. Just want to change the distributor out to something more dependable. Any good luck with the aftermarket ones? Thanks...

Aftermarket? None better than "Performance Distributors", they make 'em for YOUR application. Really woke up my '78, meanwhile I'll rebuild the OEM.

[jonmachota78]

Originally Posted by Skip Fix

They a;so have a special coil "button" that is supposed to handle more jiuce than a factory "button".

Yep ^^^^^^^ i too had problems before using the MSD coil button. I think it should be a requirement when running a bug zapper.

[Ram Air IV]

Rebuilding the HEI distributor and noticed the felt washer was missing under the pick-up coil or did the 78 Transam have one ? What type of grease is used under the plastic cap in the distributor body well ?

[Grand73Am]

Here's a previous thread about distributor grease. Looks like it's best to use just plain wheel bearing grease, not the synthetic or disc brake stuff. The plain grease will flow better in this situation. Here's the thread: http://forums.maxperformanceinc.com/...ributor+grease

[ta6point6]

I like Mallory ignitions great product but saw this on MSD site. The other guys are probably right about changing button

The Rotor Bushing supplied is a replacement unit designed for stock or mild HEI Distributors and has very high resistance. If an MSD 7 Series or Digital Series Ignition is used an MSD Low Resistance Rotor Bushing, PN 8412, must be used to prevent damage to the cap and rotor.