HEI ignition system conversion

[mrclubike]

First off their is absolutely nothing wrong with the stock BMW BOSCH ignition system
I just like to tinker with stuff and  that is why I have done this
 I have been running a HEI ignition module for quit a while with the stock electronic bean can
The problem with that is you do not get any of the real benefits of the HEI system
It basically just acts as an amplifier for the hall effect trigger  that is basically on and off signal to the coil and if you leave the ignition on it can over heat the coil and ICU if you use a low resistance coil
In order to make it a true HEI system you need a analog   type trigger.  That requires an  inductive pick-up coil and reluctor
This conversion is very common on motorcycles and cars that the ICU have become expensive or hard to get
Problem is nobody makes a reluctor that fits on the shaft in the beancan in place of the trigger wheel, so I had to make it  from scratch
I used a Pick-up coil from a Mitsubishi forklift engine because i had it
 The top picture is a trace  from a  hall effect sensor
The second picture is the sine wave made by an inductive pick-up coil.  The dwell event starts when the voltage  starts to rise and the spark occurs when the pickup voltage drops past zero

[mrclubike]

This is a picture of the reluctor that I made with a bench mounted drill press with  milling table and a 6mm end mill and hand files
This is the second one I made I didn't like the first one

[mrclubike]

This is the reluctor mounted in the bean can
The above picture is the final part after much tuning to get the timing on both cylinders the same
This picture is before tuning 
In order to tell which cylinder is retarded and which one is advanced you need a dual tower coil timing light adapter
You shoot the flywheel and then shoot the reluctor inside the bean can to tell what cylinder you are checking and then remove metal from the vane that is   advanced over the other cylinder

[mrclubike]

Here is the Pick up coil mounted onto the original breaker plate   
The Part# for the PU is a MD618624 its about $50 USD and they are only available from forklift dealers
I scrounged this one out of a forklift so it was free
I think the Pick up from a Nissan Datsun in the Late 70's would work and are cheaper

[mrclubike]

Here is the coil I used. It is out of a late 90's GM car
It has a very low primary resistance and is capable of a very high secondary voltage 
I tried to use this coil with the stock trigger but  it just got to hot for my liking
they are about $25 to $65 USD and available everywhere in the US
AC Delco Part# D555
The coil is cheap and plentiful but the MSD 8870 or 8871 coil stacker that the coil is mounted on isn't 
 
So you could run a .7 ohm Blue Dyna coil instead

[mrclubike]

This is the ICU mounted to a heat sink
The wire from the trigger has to be shielded or you will get misfires
They are cheap also $15 to $60 USD
Delco part#D1906
In Australia I think the ICU out of a Holden is the same but it has the terminals laid out differently
It is a Bosch   #BIM024

[Justin B.]

Very impressive machining on a drill-press!  Think mine's quill has too much play for something like that.  Are you sure about the set-screw to secure the reluctor?  Maybe a roll-pin through both shaft and reluctor would be a bit more "robust?"

This looks like it would be much more reliable than the current Hall-effect sensor arrangement.  Will the magnetic pickup trigger the stock ICU with Dyna coils?

[mrclubike]

Very impressive machining on a drill-press!  Think mine's quill has too much play for something like that.  Are you sure about the set-screw to secure the reluctor?  Maybe a roll-pin through both shaft and reluctor would be a bit more "robust?"

This looks like it would be much more reliable than the current Hall-effect sensor arrangement.  Will the magnetic pickup trigger the stock ICU with Dyna coils?

You cant take much off in one Pass
I was only taking off about .007 of an inch at a time
I cut away as much of the material as I could with a hack saw
 
Its a pretty close fit and its Loctited on
I may add a second set screw 
You cant run a roll pin through it
Their is a inner and outer shaft
 

I am pretty sure the inductive triggers will not work with the Original ICU

[Justin B.]

Oh, that's right, forgot about that with the mechanical advance mechanism.  Yeah, at least 2 with red thread locker.

[dogshome]

This looks interesting and makes good sense  The question is, does it satisfy the butt-dyno as well as the head? I note your comment about not knocking the standard system.

My bog standard electronic ignition does what it should according to the strobe. Solid, no flickering and generally gives me no cause for concern. I just saw some kind of snake oil video from Wedgetail Ignitions and so have my 'negative' face on. Apologies. I am fairly sure a 40 year old 2-valve parallel twin is not timing-critical. It may well show improvement by deviation functional standard kit though! Watching with interest. 

[skippyc]

I like the way you play and adapt things I go for parts for old engines and the useless parts interpreter says what engines is it off. When i tell them they look at you stupidly and say they don't have anything for that engine They can't see that you can adapt parts from other engines to fit

[mrclubike]

This looks interesting and makes good sense  The question is, does it satisfy the butt-dyno as well as the head? I note your comment about not knocking the standard system.

My bog standard electronic ignition does what it should according to the strobe. Solid, no flickering and generally gives me no cause for concern. I just saw some kind of snake oil video from Wedgetail Ignitions and so have my 'negative' face on. Apologies. I am fairly sure a 40 year old 2-valve parallel twin is not timing-critical. It may well show improvement by deviation functional standard kit though! Watching with interest. 

You are correct 
I make no claim this is in improvement over the stock system
I would recommend repairing the stock system over buying any aftermarket system
The hall effect sensor is available cheap and really not hard to replace
My bean can has over 90K miles on it and shows no sign of mechanical wear and believe me I have had it apart a lot   
The stock ICU is also cheap and available
The only thing it may improve is the  ability to start  with a lower battery voltage or colder weather
Other than that it was just something fun to make that I can actually use 

[mrclubike]

I like the way you play and adapt things I go for parts for old engines and the useless parts interpreter says what engines is it off. When i tell them they look at you stupidly and say they don't have anything for that engine They can't see that you can adapt parts from other engines to fit

The internet makes this kind of modifying a lot easier
I just look up my own parts and then go to the parts store and give them the part #
Otherwise they would just look at you stupid 

[mrclubike]

I  realized another benefit of having the HEI ICU functioning as designed
 
Since the dwell is a lot shorter with the HEI compared to the standard ignition
The electrical load is greatly reduced

True HEI dwell at idle is about 12% at 10amps as compared to the original Bosch ICU's 60% (1.5ohm coil)  at 9amps
The newer Bosch ICU is compatible with the the new .7 ohm coil and I have heard  it may also have current limiting   
 

[mrclubike]

At high rpm the dwell looks like it jumps to around 25% to maintain coil saturation