MSD rotor burn problem
 

I have 1974 911. Just installed MSD 6Al with Blaster 2. Also am using new shielded Beru wires (not copper due to relatively high impedendence). Hard to start sometimes but it runs awesome. Keep burning up rotors. Have not used a Bosch rotor yet. How to solve this?

That's the problem with having too much spark voltage/energy. The original Bosch
CDI provided adequate spark voltage & energy. Aslo, having multiple sparks causes
the life of the cap & rotor to be reduced by N (number of sparks per cylinder fire
where N is 1 to 6 below 3000 RPMs for the MSD).

Check out this web site (www.systemsc.com) on the Technical page for more info.

MSD w/blaster coil for the last year or so. Lots of miles w/no problems at all.

an old rev limiting rotor may be a prob w/ MSD? I don't like it when it's new w/MSD.

fwiw, I wouldn't be suprised if MSD eventually wears on the Beru connectors?

I don't know why the MSD (or any CD system) would supply any more voltage than the minimum needed to jump the biggest gap, regardless of the maximum capability of the box. Check plug gap (don't go crazy big) and rotor-to-cap gaps. My MSD and Blaster have given me no rotor problems (also installed Pertronix to eliminate points).

Howard

I haven't done this, since I don't use or advocate MSD ...

But, one possible solution would be to take a new Bosch rev-limiting rotor ... and 'bridge' the Glyptal-covered resistor element with a row of 5 or 6 parallel 30 gauge wires soldered to the brass ends where the resistor element terminates. Brass stock could also be used. The power rating of that resistor element is apparently too low for use with MSD, and I don't think soldering a higher-power rated resistor to the rotor would be a good idea!!!

I had this problem with a Crane HI-6 and Crane LX-91 coil. This was used with a Bosch 050 distributor, Pertronix Ingnitor, all in a 914 Type 4 engine.
It kept burning up the rotor's resistor and causing arcing inside of the distributor cap. Tried the solid copperwire to replace the resistor in the rotor. Still had the arcing. Finally went to a MSD distributor which hada larger Ford type Cap and solid core rotor...no problems then.
It seems that in my case the spark was just too hot for the rotor resistor and the Bosch cap spacing to close for the increased spark also.

"I don't know why the MSD (or any CD system) would supply any more voltage than the minimum needed to jump the biggest gap,"

Ask MSD that question. That's their big selling point. Many get "sucked" into that B.S. hype.

Do a search, many have reported this problem.

with a GM car had the same problem with the hi 6 and MSD because the pin from the center of the rotor needs to lower resistance than a stock one.

if the rotor has a resistor then do as Warren said and bridge it or use a solid rotor and that will solve your problem.

Warren - what is your preference for a CDI unit?

If it's a rev-limiting rotor, I think there's a solid (no resistor), VW-Bosch rotor that can substitute. One shouldn't need a rev-limit rotor with an MSD which uses chips to limit engine-fired rpm.

Sherwood

MSD.....Works!
 

I have had an MSD 6A and Magnacor wires on my SC for over a year now. No problems with the cap rotor, wires, plugs or anything else associated with the ignition system. Of course, the SC distributor does not use the rev limiter rotor so any problems with the rotor resistor is eliminated. I certainly don't feel that I was "sucked in" by any MSD advertising! The ones that are getting "sucked in" are the Pcar owners that shell out $400 or more for a reconditioned Bosch CDI!

Fred Cook
'80 911SC coupe

"The ones that are getting "sucked in" are the Pcar owners that shell out $400 or more for a reconditioned Bosch CDI!"

That's why Bosch and OEM car manufacturers laugh at the MSD technology and
at those that believe in the hype. If the technology had ANY merit, Bosch and/or
the OEMs would utilize it. There's nothing complex/unique about the design.

It's kinda like the "turbo" unit they sell to insert in the fuel line for better mileage
and performance. There's always someone who will believe the hype!

"That's why Bosch and OEM car manufacturers laugh at the MSD technology and at those that believe in the hype."

Loren,
Just curious. What part of their spiel do you consider "the hype"?

Thanks,
Sherwood

Who's getting sucked in?....
 

Hmmm, $400 for a rebuilt Bosch CDI or $150-200 for a new aftermarket unit that works just as well (maybe better, but we won't go there)! The extra $200-250 bucks might be worth it to the purists that insist on keeping their cars absolutely stock but is hard to justify for anyone else! I guess ole P.T. Barnum was right....There is one born every minute!

Fred Cook
'80 911SC coupe

Ditto
 

MSD Digital 6+
High Vibration Coil
Magnecore Wires

3+ Years with no problems

To quote Steve at Rennsport System's Web site:

....replacing the stock CD amplifier and coil with a High-Voltage, High-Current unit such as the MSD-6AL or Crane Hi-6 and their respective matching coils. These units provide a FAR hotter spark that is better able to fire the rich idle mixtures required by Weber carburetors and MFI as well as firing the wide plug gaps that have been proven necessary for best power. These ignition boxes can make a race-cammed Webered’ high-compression engine idle for hours without any signs of distress when installed properly. The multi-spark high current ignitions really help reduce the cantankerous nature of some carbureted and injected engines that have mixture troubles caused by big venturies and high-overlap cams. These ignitions also feature some nice adjustable soft-touch rev limiting.

It's your money. I paid several hundred less for the MSD and never looked back.

"These units provide a FAR hotter spark"

That's the problem, and that's why ignition parts burn! Well said.

Bottomline:

If a Bosch unit had been used, then this thread would not exit!

"These units provide a FAR hotter spark""

Yeah, marketing hype, but apparently the multiple spark units help idle and low speed running on early Weber and MFI engines. Not sure there's a demonstrable difference in a CIS engine other than replacement cost.

Sherwood

This comment is not relevant to solving the problem.

BPlante,
Just b.g. info that goes with every thread discussing MSD, Crane and Bosch issues.

Back on the subject at hand. You first stated:
"Keep burning up rotors. Have not used a Bosch rotor yet. How to solve this?"

Whose rotor are you currently using?

Sherwood

afaik a CDI is able to better control combustion. It can be by extending the spark duration or multi-sparks in the envelope.

question
- Is the Bosch spark duration fixed thru the whole rpm range?
- Is the MSD lower rpm time of multi-sparks = Bosch duration?
- Is the MSD upper rpm single spark duration = Bosch duration?

huh?

ok.. If mine I would first try a non-rev-limiting-Bosch rotor. Then if still toasted terminals I would also change the Beru plug terminal wires.

all of above is a prejudical rant.

- Is the Bosch spark duration fixed thru the whole rpm range? Yes


- Is the MSD lower rpm time of multi-sparks = Bosch duration?

The key is the length of the INITIAL spark! The other sparks occur TOO late (>2.5-5ms)
and they have NO value. There's no more fuel charge energy left when the next spark
occurs to produce any additional combustion and force on the piston. That's why Porsche
used dual plugs in some of their engines, e.g. 964 & 993.

Note: At 1000 RPMs a piston moves 6 degrees every millesecond. So buy the time
the next MSD spark occurs (5ms), the piston will have moved 30 degrees. At 3000 RPMs
the piston moves 90 degrees. The combustion process is completed in about 2ms.

- Is the MSD upper rpm single spark duration = Bosch duration? Yes

Come on guys. Think about what's really occuring in the combustion chamber
at ignition time. Porsche and Bosch have thought about it and have concluded
a multiple spark CDI is B.S.

Bottomline: There's thermodynamic/scientific theory which supports the B.S.
If you want a little better idle, gap the plugs at .045 - .050 with Bosch CDI.

Like other "no basis" mods, if it makes you feels better, do it!

burned rotor
 

Echlin. I am beginning to wonder if the problem lies in the shielded Beru wires, even though they are not solid core.

bplante,

If you have new OEM shielded wires, then they are, indeed, copper-core wires ... with an incoporated resistor in the Beru connector! Both ends are removeable ... just unscrew.

My suggestion is to gap your spark plugs at 0.040" maximum and most likely your burning rotor problem will disappear!

"The key is the length of the INITIAL spark! The other sparks occur TOO late (>2.5-5ms) and they have NO value. There's no more fuel charge energy left when the next spark occurs to produce any additional combustion and force on the piston. That's why Porsche used dual plugs in some of their engines, e.g. 964 & 993."

Thats odd, I have two seperate mags and twin plug, left mag top right mag bottom, on my engine, one timed at 24 and the other one at 26, why would I get an rpm drop when when I switch from left and right if everything is already burned?

Craig

"why would I get an rpm drop when when I switch from left and right if everything is already burned?"

Sounds like you have a real problem! You might put it on a dyno and vary each's timing
rather than guess at what's happening.

So using 6 degrees every millisecond @ 1000 RPMs, then 2 degrees (26-24) equals
.300 ms which is much less (1/10) than what the MSD can produce with
the next spark (2.5 - 5ms) - no real benefit.

Since OEM car manufacturers are continually under pressure to reduce emissions and
if the hype about a MSD system had merit for better combustion, don't you think they
would utilize some form of a simple mulitple spark system?

Not Getting the point!....
 

I won't mention any names, but someone here is just not getting the point! Why spend $400 (or more) for a "REBUILT" Bosch CDI unit when the problem can be rectified (pun intended) for $200 or less using quality components? Oh yeah, someone needs to keep the MYTH going that only Bosch can build a reliable ignition! Well, I won't tell if you don't!

Merry Christmas to All and to All a good night!

Fred Cook
'80 911SC coupe (MSD energized and loving it!)

"Why spend $400 (or more) for a "REBUILT" Bosch CDI unit when the problem can be rectified (pun intended)"

So after all the mickey mouse wiring mods. e.g. constant +12, and the time spent
to install it, e.g. modify the brackets, you have an engine compartment that no longer
looks stock Porsche, but one waiting for the Chevy engine install.

Bosch Humbug!....
 

That's ok, I'll laugh all the way to the bank! Besides, there is really nothing wrong with a hot small block chevy V8! There is an old saying that goes something like "If you are not growing, then you are dying." Sometimes it pays to look and see what is new in the world, even the Porsche world.

Fred Cook
'80 911SC coupe

I use the MSD-M marine version.. who knows?

I figure if it's reliable in an ocean racer how bad can it be? I always had to ride it them with bent legs 'cause those are pounding machines. A tight jock strap helps also. Their engine compartment are good for heating cold coffee also 'cause their so hot.. whatever floats your boat.

If you don't like the idea of an MSD install, don't do it. If you do it and then decide you don't like it, take it out. If you like it, leave it.
I can't believe the ammount of debate these things cause.

I can...

The endless quest for a deeper understanding of combustion is somehow like looking into the universe imo. The waves of energy, it's control, it's efficency, etc is the stuff motor-heads dream about. The blending of reversion lower energy electro-magnetic particles with higher energy particles is like stroking to the climax of power.

but you can't come without the necessary spark imo.

Merry Christmas Ronin. I guess that is what this debate is really about. The only reason I'm being blase is that:

1) I have MSD and am happy
2) I would be equally happy if I had CDI
3) I would even more happy if I could do a US road trip/911
5) ditto for being P. Car test pilot at the 'Ring
4) Combustion, petrol & electricity...MMMmmmmmmmmmmm

Ok, I understand...

Merry Christmas Matt

To fix your rotor burning problem, ditch the factory wires and get some Magnecores.

Like Warren said, those stainless braided wires are copper core with a resistor in the plug connector. You need a good set of 8mm resistor core plug wires. MSD specifically recommends against copper core wires.

BTW, I suspect it's not the voltage that's burning the rotor, but rather the amperage that's flowing through the rotor's resistor with the relatively low-impedence copper core wires.

I've fixed this very problem a number of times on customer's cars by swapping out their factory wires for the Magnecores.

I've had MSD on the P-car for over 2 years, no problems even with my slightly rich idle for smoother midrange power. I've also had MSD on my drag car, four trucks and two other street vehicles IIRC. Never a problem except one dead box. MSD equipment is used to fire Top Fuel drag motors and fire so hot they melt the plugs halfway down the track (magnetos), just about every form of racing uses MSD particularily when carbs are required by the sanctioning body. The single biggest gain of installing an MSD box is the soft touch rev limiter. I used 3 limiters on the drag car, one for total RPM, one for burn out and one for the starting line. Hold the button and push the pedal to the floor, the engine "stutters" against the limiter at the set RPM ready for launch, if it was good enough for a motor that cost me more than twice as much as my 3.0 SC motor, it's good enough for the P-car. I can think of a few times the bad synchro in my 901 box caused me to miss the next gear and the rev limiter kicked in saving the engine from an over rev and possible damage. I simple don't and won't trust mechanical limiters, having seen the results of a failure more than once. BTW my SC motor runs Zeniths with 36mm venturis, headers, stock dizzy, cap and rotor, and plug wires. I run slightly cooler plugs at a 0.050" gap.

Back to your question, are you changing the cap AND rotor? If the cap has too much clearance and you're only replacing the rotor that could be part of the problem. Also check the intalled height of the rotor, if it's somehow too low that can cause problems. Tyson's suggestion of Magnecors sounds good, that's one of my planned winter upgrades.

"BTW, I suspect it's not the voltage that's burning the rotor, but rather the amperage that's flowing through the rotor's resistor with the relatively low-impedence copper core wires."

I (current) = V (voltage) divided by R (resistance)

So it's also the voltage, right.

Bottomline:

Two choices;

1. lower the voltage, put a stock Bosch CDI on
2. increase the series resistance;
a. different spark connectors
b. use resistive wire

Copper vs steel vs XYZ metal (R<1-10 ohms) won't change the resistance that much.
The current is affected by:

1. spark plug connectors (500-5000 ohms)
2. coil connectors (500-5000 ohms)
3. rotor resistance (500-5000 ohms)
4. cap carbon wiper
5. the discharge ionization at;
rotor
spark plugs

Too much guessing on this thread! So what could be the problem if stock Bosch CDIs
don't burn ignition parts & MSDs claim more voltage, energy, & MULTIPLE sparks?

Now let's think hard!

There is only this much debate becuase Loren rebuids Bosch units and needs to bolster a market that is shrinking becuase many people prefer the performance and cost of aftermarket CDI's