I have a BB Rajo head and these cylinder heads are designed for dual ignition. I was looking for a relatively easy simple solution. Previously it has been pointed out that a mid '80's Datsun/Nissan used a dual plug head. Upon checking I found that the cap and rotor was still available locally. This unit used electronic ignition and I would prefer to avoid this for simplicity and reasonably correct appearance. Yesterday I remembered that Onan has built a 2 cylinder engine for many years that utilizes the "waste spark" approach. The coil has two high tension connection and they both fire every time. Today I visited the Onan dealer and he was very helpful. There appear to be 3 versions of this coil. Two are even 6 volt and one as 12 volt. They are all designed to work with point ignition. One of the 6 volt versions even LOOKS RIGHT!! So I have ordered one 12 volt and one of the 6 volt
I have bought a cap and rotor and I feel they will be fairly easy to install on a Bosch or similar T distributor. The rotor fits on a larger diameter shaft that the Bosch has, so a simple sleeve adapter should work there.
The cap is also larger so a simple machined aluminum plate should work there as well.
I will probably go with points and condenser, but a Pertronix should also work.
Cap; Intermotor JH129
Rotor; Intermotor JR114
Coils; Onan; 12 volt,166-0535;6 volt, 166-0792 or 166-0346
Do you expect to fire both plugs from the same coil?
I used to own one a 1987 Nissan pickup with that setup, it used two coils, each with their own separate coil wire that went to the two center terminals in the distributor cap.
One other feature of the Nissan setup that I recall is that the spark plugs on one side of the cylinder head were a different heat range from the ones on the other side.
YES!! Onan has been doing it for 50 years with this coil
I must be missing something. It would be too much gap if both plugs are on the same cyl, as both would have to fire across high compression.
I guess I will find out!!!
Well another method would be 2 6 volt coils in series on the primary fired by one set of points on 12 volts. BMW motorcycles have been doing it for 45 years. Both plugs on an air cooler bmw fire every time and I have never heard of a problem with the method.
Just curious Les, how will you know that both plugs are sparking under compression?
That's a interesting idea
I can test it by shorting out one of the plugs (or all four on one side) I should notice a reduction in performance (or idle speed)
In a waste spark lashup, the waste spark is firing across a .030 gap at near atmospheric pressure, which takes not much voltage. The other spark is firing across .030 at 5 atmospheres, which takes thousands of volts.
If the waste spark end is also firing across 5 atmospheres, the coil will have to build up almost double the voltage. Expect hard starting and overheated coil.
What you have conceived is novel, indeed.
I hope find out in a month or so
IF it doesn't work I can mount a second set of points and a second coil and I am not out much. If it does work, I will make a lot of people's projects easier.
"Synchronizing " two points won't be too tough. I can use a pair of light bulbs and slowly turn the engine and tweak the gaps until they fire at the same time. Hopefully I won't have too
I'm not convinced of your "science", but I can't disprove it
Just place the plug wire from the second (waste side)tower to the cylinder 360 degrees off from the cylinder at TDC.
(Message edited by adminjerry on March 04, 2015)
Les,this is very interesting as my son has a BB Rajo and needs to solve this problem too.Please keep us posted.
That is a excellent idea, as it will be a good way to test whether I am right or Ralph is right. The Nissan cap as clearly identified as to where each terminal is supposed to go, so swapping wires at the cap is simple (keeping in mind the T firing order)l
I post these things for two reasons;
1. A good well reasoned "critique" is valuable.
2. If I can help someone else, that is good too. I believe about 30 of the new BB heads are out there and I suspect that some are still "gathering dust" (like mine). Solving the dual spark will help get more of them "on the road"!!
How are the double magnetos often used on aero engines usually set up?
Are the magnetos that are meant to work together checked and adjusted so they'll follow the same timing advance curve?
Some pictures of the rotor and cap just sitting on a Bosch JF4 distributor
The rotor will have to be "raised", which is great. It needs a adapter and making it to elevate the rotor is simple.
To mount the cap will not need much more than a aluminum disc mounted to the outside of the distributor body (and a pair of lugs located with the "clip" screws should do the job nicely. The cap is held down with two screws, so that is simple too.
The distributor is from one of the reproduction Bosch front plate distributor units. It is securely mounted so the little bit of extra weight shouldn't cause any problems.
Yes. They want two independent ignition systems for reliability. As I won't be leaving the ground (at least I don't plan to), I'm less concerned about reliability.
Also keep in mind that airplane engines are operated much more like stationary engines. They are either idling or running at high speed. The torque curve during acceleration is not particularly important. So as long as the spark timing is good at idle and is good at full speed it is fine. For a car we want the timing right at all intermediate speeds at full torque rating. On a T of course we have the left lever and our "ear" to accomplish this. This distributor setup has the centrifugal advance disabled and relies on the driver to do the job.
I may decide to re-install the automatic advance as this car is destined to be driven by my wife and she would probably prefer to be able to ignore this requirement.
Think that through, Jerry. How do you fire the second plug?
That bothers me as a spark will travel the path of least resistance.My Son's BB is an original,not a new one. I have a new Mag for a Wisconsin V-4 engine,if only I knew how to adapt it??
In had a 86 Nissan truck with dual plugs it was my first car. I own a 96 now with single plugs same motor. I guess there was no need for dual plugs
Les, been in the shop all day, can you call me Thursday afternoon. 785 259 1620 Jerry
This is a great modification already being produced using the same cap and rotor. I recently purchased the Bosch front plate patterns from TW Components and hope to copy this design and adapt it to the Bosch plate as a addition to our RAJO dual plug head kit. I purchased their kit and will be copying most of it for this project. Because I believe it is important to share knowledge with fellow model T speed freaks, here is the link for those who may be interested. http://awesomepowdercoat.com/twin_plug_ignition.html
Great news. I approached Pertronix but could make no progress. Good that some one else did. I'll be starting on mine next week (as soon as I finish the first Ross steering box for testing). It will be good to potentially have a choice of electronic or points and condenser!!! I hope to test fire mine in about a month
Does your dad sell just the gears for the distributor drive? I have a original Bosch distributor for a plate drive, but need the gears!!
I know about busy in the shop. Hard at work on the steering box project
The Onan coil is special as it has TWO high tension connections. I believe that they come from opposite ends of the high tension winding. A good friend built a T ignition using the '80's Ford duraspark and just two T coils. He brought the other end of the high tension out and so fired two plugs from each T coil. He is still using it and it works great!!!
Glad to hear you are making progress on the ross steering box project. Please let me know when you will be going into production. I want one or maybe more.
Hey Les - I see now why you are looking for a "Workable" choice. I tried to find some of the old school dual spark systems and man they are as rare as hens teeth.
Bosch made a ZR4 mag with twin spark (that'd be me first choice personally) but I can't find one ANY where.
And there's a Delco Remy setup with two separate 4 plug distributor caps (and thus two different coils) on one body but I can't find a model # or any proof that it exists somewhere other than in a picture in another thread on this forum.
The other thing I have seen is on Mark Chaffin's Joe Gemsa engine he rebuilt there was a Delco Remy twin spark distributor that had 8 plug wire spots but two different coil inputs in the center. I can't find one of those out there anywhere either.
Mark (and others). I have this nagging suspicion that I have heard that the VW beetle engine had ONE cylinder timed a few degrees "off" intentionally. That apparently they don't fire evenly intentionally. True or not????
Yup. That is the problem!!!!
Yes, I've seen the VW timing issue discussed. They had an oil cooler that stopped some of the air flow to #3 cylinder, so instead of moving the oil cooler they changed the timing on that cylinder to prevent overheating problems.
I had a #3 piston in my bug melt, it sounded like someone threw a hand full of pocket change in the engine. Was not a pleasant experience
I was sure I had heard something like this. I wonder if the Bosch JF4 distributor (which is supplied with the reproduction plate mount) is timed this way???
Just did my own research. It appears that the JF4 is spec'd for the Alfa Romeo, where as the JFU4 is the VW version. Well that is a relief!!
I just went on Lang's website and I see that various distributor drive gear sets are available, so I can probably rebuild the old original Bosch distributor body I have.
Les and Mark,
I am really interested in this topic. I have a Rajo BB and BBR ready to install. I need a twin spark set up!
I purchased a complete Datsun twin spark distributor with all of the wiring. This particular model has external modules which are ugly. Apparently there is another Datsun twin spark unit with internal ignition modules that looks much clearer. This distributor can be adapted to fit into the Bosch front plate. Dan McEachern may make the gears.
Jim Cullinane wrote an article about the Datsun twin spark distributor conversion in one of his speedster books. I will see if I can find it.
I found this Alpha Romeo site which has some info on a twin spark distributor set up:
Mark, I am willing to be a guinea pig if you need to test prototypes of your twin spark distributor.
Please do share the Jim Cullinane article if possible. This is an interesting topic to me also, I just finished a front plate conversion of a twin spark Datsun dist. with the internal modules but the wire nest goes into a terminal block and I am confused how it gets wired up. I would like to do a second modern conversion on another front plate.
I do have twin spark mags and one of those side drive twin head dist. off a Stutz and being side drive they are more proper for a twin spark head as usually a motor built like that will need an oil pump that is normally on the front where the dist. is located.
I have wanted to contribute to this thread with some photo's but got my hand tangled up last Sun. splitting wood and not all fingers are working.
All- if you plan on running the Datsun dual ignition distributor, they rotate the opposite direction from the Bosch distributor. If you want to know more, send me an e-mail. dmcgearsatyahoodotcom.
The Jim Cullinane article is copy righted and the cover of the booklet states permission is needed to duplicate. I will try to contact Jim's family to see if I can post the article.
I think a similar article by Jim may have appeared in a SOSS journal.
I bought my Rajo BB from Howard Genrich. Howard had given me some info on the Datsun distributor conversion. I will check to see if I can find it.
The stuff I have found on Alpha Romeo and VW dual spark distributors that use the Datsun cap and rotor make the wiring look pretty simple.