Just a theoretical question… suppose I would fit an ignition to a Scott that sparks both in TDC and in BDC (in the same cylinder). Would that work?
I know there are 4 stroke ignitions that spark on both work stroke as on exhaust stroke with no ill effect. But would the same go on a twostroke? At the moment just before BDC the cylinder is already filling up with fresh mixture. This is of course not yet under pressure. So when the plug sparks, would that still ignite the mixture or no?
Just a bit puzzled…
An “idle” spark on a 4stroke has no measurable effect because there is no burnable mixture in the cylinder. Thus it has no effect on the engine and can simplify the timing train. It might be employed for example to save weight or for cost of manufacture.
A 2stroke on the other hand always has a burnable mixture somewhere about it. (Even if it is only the nearby air being lit by the rider’s language when the blighter won’t start…!) Therefore an idle spark on a 2stroke can serve no useful purpose and may even result in unpredictable misfires, I cannot imagine any reason why it could be of benefit. By and large I’d say it’s better not to go there.
Well.. I can only say that ive got a wasted spark on my system and it doesn’t seem to bother it..
I guess there is in theory a conflict possible but i know from bitter experience that its a bugger trying to start most engines when the compression is down, so the chances of ignition occuring at nearly B.D.C. are a bit slim..
Saying that Ive got no actual proof that it doesnt interfere with the process somewhere, but it does seem to work ok.
I hope the bike is coming on ok..
I’ve seen a page somewhere on the web that offered electronic ignition kits for two strokes (not for Scott….) and these kits had a wasted spark. This set me thinking or this would work (in theory).
Not much done on the Scott for a while Richard… Getting used to the “daddy role” takes some time… time not spend in the workshop.
I’ve put the pair of 600 shortstroke pistons I have in some Diesel to loosen the dirt. That was about 1,5 months ago…
I had a similar problem with my rolling chassis. It took years of sitting on the bench until all its internal stresses had relaxed enough to proceed safely.
I applaud the patience you must have to let the neccessary cleaning cycle take place with your pistons. Like leaving a fine wine to achieve its potential. So many people would approach this process with haste, but they will never have the ‘seasoned’ internals that will grace your machine, and the inner calm of one that knows that such fine quality cannot be rushed.
Just a note to add to Richard’s entry.
Some years ago I was trying to increase power on the racer. The engine felt like it was just running out of steam, but it was doing it too abruptly to convince me it was a normal condition. I built a mag test rig and found that the mag points were bouncing at over 3500 revs. (Like valve bounce) The loss of spark timing accuracy and efficiency was resulting in engine roughness and power loss. I rebuilt the BTH mag as best as I could, but could not eliminate all the problems. In normal running on a road bike, you would not notice and just think that you had reached the limit of what the engine had to offer. I bought some PVL electronic ignition components from Rex Caunt and manufactured a “One off” conversion into a traditional BTH mag body. The one drawback was that for space considerations, I could not get two pick up coils in and so it was run at twice engine speed with sparks at both top and bottom. This worked fine and far better than the traditional mag, but it had one penalty. Whatever the backlash / lost movement in the drive system, causing timing firing point variation, then as the rotational speed of the mag was doubled, then the range of possible error was doubled.
Other than that, this wasted spark system worked just fine on the racer for years helping to give an output well above that normally attained with a Scott, so don’t worry, it will work ok.
When my friend Tony Harris carried on development alone, that he had started with Rex Caunt, he produced the new BTH electronic magneto. He wanted to test this under the most rigorous conditions and the Scott engine speed mag application has long been recognised as demanding. We had a prototype BTH mag on our racer and it has given perfect results and reliability for several seasons now. I recommend the new BTH mag as the very best, if you can afford it.