Retard box

[gripper]

Does anybody know if it is possible to repair and test the retard box fitted to IP2? They must have tested when they were made. Has that information been lost?

[Richard Negus]

One of Shenstone's inspectors, Paddy Ryan, tested and repaired all the Sparkrite boxes and also checked the Boyer boxes, using a small oscilloscope and a pulse generator.All that equipment is long gone, the knowledge remained with Paddy as most it was word-of-mouth from Sparkrite.I have a s/h retard and ignition unit that are believed good, if you'd like to borrow for comparison.R.

[FloridaMike]

Bit of translation from English to American requested here - a "retard box" sounds like something which could get you declared supremely insensitive or even politically incorrect . . .Is this a knock sensor? (Sheesh, that doesn't sound much better.)OK, I'll try it again - is this item a pizeo-electric sensor which detects pre-ignition and retards the timing to compensate?Best Regards,FloridaMike

[Malc]

Whats that about retarded boxers, you could get a fat lip if you call them that!Nothing as fancy as a knock sensor, just retards the ign when hot to give a nice tickover, that is if you prefer a nice tickover to good throttle response.On the police bikes, some had poor throttle response and would need a second twist of the grip to get the engine out of the retard hole it had dropped into which made pulling out of junctions very dodgy.I was sent retard boxes that were adjusted to different degrees of retard to try and cure the problems which they didn't. To make matters worse, the ones fitted at the time were not very waterproof so when it rained a rider would come in with the engine stuck at 2000 rpm as the unit would not work until it dried out.I by passed the wiring and ran a bike around on test set fully advanced, about 1000 rpm was typical for tickover. This gave instant throttle response and better reliability but I could not let a bike out in service like this without the approval of the factory. John Nelson ( formerly of Meriden) was the service manager at the time and said if they could set up a bike and test at 1000rpm tickover fully advanced the a fax would be sent to police HQ to approve. This was done and then all the retard boxes on the police bikes were junked. So it comers down to a decision of having that lovely sounding low even tickover or having good throttle response and I, like the police riders, much prefered the latter.Malc

[FloridaMike]

Sounds to me (from here, far, far away, and never having seen one) that this just might be a simple thermistor (positive or negative temp coefficient) plus a tiny potentiometer for the final adjustment . . . ?But why would you need a scope and signal generator to adjust that? Scope + sig gen is for knock sensors, all this would need is the tachometer. (Voltmeter if you were curious about what the box is telling the advance, but not necessary.)Howzis work, anyway?Best Regards,Florida Mike

[Interpol2471]

Mike the ignition retard box is controlled by a simple thermistor placed on top of the engine as the switch but the retard box itself being talked about here is much more complex and actually uses an ignition retard circuit set up using multiple potentiometer set variables to control the waveform to offset the ignition curve (up to -50 degrees) and has a number of pre set resistor circuits as well as a number of ic's to control the gated outputs. I have not really studied the boxes but I have three here that I was going to play with by injecting various pulses to simulate the ignition and look at the waveforms but I have never got around to it yet. A friend of mine works for Kent Cam's and he was also going to have a look and compare the circuits to modern electonic ignitions but he also is as slow as me

[Richard Negus]

Hi FMike,The thermal switch, fixed to the r/h housing on an air-cooled, changes from OPEN circuit to CLOSED at around 65C, effectively telling the ignition system that the engine is either COLD or HOT. The Sparkrite (there's a contradiction !) ignition system comprises two 'boxes' ; the ignition 'box' converts the minute signals of energy from the flywheel trigger to 400volt pulses to the ignition coils, and hence to the spark plugs, with almost no delay giving a fixed ignition timing of around 18deg BTDC. For all normal running conditions, that works perfectly ok but idle speed is usually in excess of 1000rpm.The Norton rotary, with roller bearings and oil-mist lubrication, has comparatively little internal friction and requires only a small amount of fuel/air mixture to idle smoothly at 5-600rpm. The Norton system of completely closing the butterflies and having a regulated idle bypass is an attempt to overcome flow variations ; Mikuni carburettors of the F1, being precision machined items, are much better at controlling idle air flow and do not need the bypass system.The second Sparkrite 'box' introduces a variable (and adjustable) delay between signal and pulse, ranging from around 55degrees at idle speeds to zero delay at 2,200rpm. With 55 degrees of retard, the plugs are actually firing at 37degrees AFTER TDC ; this is ok for a new engine, but a low compression one may slowly wither and die whilst idling, or not pick up cleanly.Both Sparkrite, and the later Boyer, had an in-built flaw in that restarting a hot engine was made more difficult as the timing at cranking speed was 37degrees ATDC. More recent 'digital' ignition systems for the rotary have a facility whereby a hot engine is given zero retard for a limited number of engine revolutions. This has made a significant improvement in hot re-starting.The delay 'box' (aka 'retard box') and the ignition 'box' were invented before ic's were common and each contains a printed circuit board with electrickery such as resistors and capacitors; they're not weatherproof and suffer corrosion. The retard box does have the advantage, however, that its characteristic can be 'tuned' to suit individual engines. There are two little pots under the lid that can be twiddled to modify the speed/delay curve and, no, I don't know how to do it ! Paddy was the expert and labelled each box with the results of his check.Signal generator and scope are required as it is a dynamic check. The scope shows both the input pulse from the signal generator, the delayed output pulse, and the true frequency.I think I know what I mean, anyway ! R.

[Interpol2471]

Sounds like me also Richard I know what I mean in my own world but outside it's a mystery .... I wrote IC's instead of caps above but that shows that maybe I was thinking of work lol I know I have never seen an IC in one yet DOOH !!!!I must start looking at these boxes I have here as I am sure they will make sense once we start playing with them.The one fitted to my bike has been humisealed so should never suffer the water issues and I can do that for anyone if required.

[gripper]

Before my engine rebuild, my retard box worked well though it did lead to a couple of heart-stopping moments (that nearly lead to a permanent heart stopping) when pulling out in front of traffic like, you do on a bike. I have been plagued with a slight miss-fire when riding on a cold engine that disappears after two to three miles. I removed the retard box to eliminate it from the equation but the miss-fire persists. When I replaced the retard box, the 2000 rpm tickover is exactly what I had, with occasional dips to less than sustainable tickover speeds. I've removed it now and I'll accept the uneven tickover and good responce. I'll start saving for a digital ignition box.