Interspan ignition set up

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Has anybody used an Interspan ignition. I'm having a problem getting my latest project to fire up. I could use some help with the setting of the contactless trigger unit, as I can't get hold of Fred at Interspan at the moment.

Martyn.
 

Fast Eddie

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So long since I ran Interspan Martyn I can’t help.

So, you got it on an Enfield ??
 

Chris

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Hi Martyn
The rotor has a line marked on it. You line that up at top dead center. Fred told me to mark my own lines as I was using Triumph ones lol. I have diagrams & spares.
Chris
 
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Hi Chris/Eddie,

The bike is the ex Hitchcocks 612cc Big Head scrambler. When I got it it had been running on castrol R & burning methanol. I've stripped the engine, cleaned out the R, dropped the comp. from 12:1 down to 9.7:1 & rejetted the 1000 series Concentric to run petrol. The twin plug ignition has been rebuilt by Interspan & is sparking fine. Should the magnet in the rotor line up centrally with the pick up at TDC, or be 34 degrees BTDC. I'm not sure where the magnet starts to take effect if you know what I mean. I started with the ignition set as it arrived as I took a photo before I dismantled it, but all to no avail.
 
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I’ve run an Interspan ignition for about 30 years on my NRE Weslake twin and fortunately I haven’t had to think too hard about setting up the trigger timing since, like Chis, I just line up the scribed line on the pickup coil assembly with the scribed line labelled TDC on the rotor. When I did try and figure out why the magnets were where they were I got confused pretty quickly.

I have Interspan rotors for the Weslake engine and one for a Commando engine and these engines have the cam turning in opposite directions ( when viewed from the timing side, cw for the Weslake, anti-cw for the Norton)

On the Weslake rotor the centerline of the magnet hole is about .15“ below the scribed TDC line (with the scribed line at the 9 o’clock position) which implies the magnet centre is actually passing the centre of the pick-up coil pole piece after TDC

Similarly on the Norton rotor, the centerline of the magnet hole is about .18“ above the scribed TDC line ( with the scribed line at the 9 o’clock position) which also implies the magnet centre is actually passing the centre of the pick-up coil pole piece after TDC. Given the different cam direction this is consistent with the Weslake set up, although the Norton does have a bigger magnet hole as do the later Weslake rotors.

It seems from the above that there is enough magnetic field strength as the magnet approaches the coil pole that it generates enough voltage in the coil to trigger the ignition at the right number of degrees before TDC.

It also occurs to me that with a single you might need to pay attention to whether you’re timing it on the compression stroke if you only have 1 magnet on the rotor (assuming on the RE, the rotor is driven from the cam) My rotors are cam driven but have 2 magnets 180 degrees apart so it fires like a conventional 360 twin with wasted spark. Hence it doesn’t matter if you time it on compression or exhaust stroke. I might matter on your setup. Given that the engine was working and that you had made a note of the rotor position before pulling it apart this might account for your problems.

I hope the above might help and you’ll get it going again.

Duncan
 
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I’ve run an Interspan ignition for about 30 years on my NRE Weslake twin and fortunately I haven’t had to think too hard about setting up the trigger timing since, like Chis, I just line up the scribed line on the pickup coil assembly with the scribed line labelled TDC on the rotor. When I did try and figure out why the magnets were where they were I got confused pretty quickly.

I have Interspan rotors for the Weslake engine and one for a Commando engine and these engines have the cam turning in opposite directions ( when viewed from the timing side, cw for the Weslake, anti-cw for the Norton)

On the Weslake rotor the centerline of the magnet hole is about .15“ below the scribed TDC line (with the scribed line at the 9 o’clock position) which implies the magnet centre is actually passing the centre of the pick-up coil pole piece after TDC

Similarly on the Norton rotor, the centerline of the magnet hole is about .18“ above the scribed TDC line ( with the scribed line at the 9 o’clock position) which also implies the magnet centre is actually passing the centre of the pick-up coil pole piece after TDC. Given the different cam direction this is consistent with the Weslake set up, although the Norton does have a bigger magnet hole as do the later Weslake rotors.

It seems from the above that there is enough magnetic field strength as the magnet approaches the coil pole that it generates enough voltage in the coil to trigger the ignition at the right number of degrees before TDC.

It also occurs to me that with a single you might need to pay attention to whether you’re timing it on the compression stroke if you only have 1 magnet on the rotor (assuming on the RE, the rotor is driven from the cam) My rotors are cam driven but have 2 magnets 180 degrees apart so it fires like a conventional 360 twin with wasted spark. Hence it doesn’t matter if you time it on compression or exhaust stroke. I might matter on your setup. Given that the engine was working and that you had made a note of the rotor position before pulling it apart this might account for your problems.

I hope the above might help and you’ll get it going again.

Duncan
Hi Duncan,

The rotor assy. is on the crank on my bike (single cylinder) & what you are saying regarding the line on the rotor & magnet position holds true. This is what I couldn't understand, as the magnet passes under the pickup after TDC which seems odd. Having said that, when set in this position, as indeed it was prior to the engine strip, the bloody thing still won't fire up. I have even tried fitting the carb off my mates Norstar just to check it's not the carb, but with no success.
Not sure what to try next.
 
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Just managed to speak to Fred at Interspan. He's going to test the whole setup for me, so watch this space.
 

Chris

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Hi Martin
Have you got a photo of you rotor & pick up?
 
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Sorry Chris, can't do photos but the rotor is 35mm dia. with a scribe line on the front face. The magnet is approx. 15 deg. clockwise of that. As this is a crank driven setup this means the rotor turns anti clockwise. The pickup is a 25mm long ally block with an earth lead from one end & the signal lead from the other.
Speaking to Fred he seems to think that it is a fixed ignition, as it previously ran on alcohol, & maybe why I am getting violent kickbacks. Apparently this trigger system can be changed to give several degrees of advance which would help.
And yes, Fred is the man...........who can only be compared to a certain Tony Haywood!!
 
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I am now looking at alternative ignitions for the 612 Enfield. Sadly I think Fred has lost the plot, as all I get when I actually manage to get hold of him is his life story. I have had this bike for nine months now & still not heard it running, purely down to the lack of ignition. I would prefer not to have to fit an alternator & battery or powerbox as I don't intend running lights, so a magneto would be great, but as I would like to keep a twin plug set up the only mag. I know of that will achieve that is the very spendy BTH electonic one.
If I hadn't heard so many horror stories about Electrex World I would try their set up. PVL also make a similar ignition but I don't know if it's any good.
You chaps got any suggestions?
 
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