Not just you, have had the same pointless conversation with the previous and the current owner, maybe we can blame my Scots twang as well but no common sense answers were available.
E: Engine BTH magneto
- Thread starter Sakura
- Start date
But remember single or twin plugs I could see no difference on the roller performance graphs perhaps with a more modern head architecture you would
each time I altered the timing to obtain best performance while on the rollers a simple task with the slotted BTH (this may explain why I dont use any fancy timing setting gear like a strobe when sorting the racer) in other words I find the best setting and then record it.
each time I altered the timing to obtain best performance while on the rollers a simple task with the slotted BTH (this may explain why I dont use any fancy timing setting gear like a strobe when sorting the racer) in other words I find the best setting and then record it.
Tim,
I don't think that is the way to asses the value of twin plugs. I have had several racers say they did not switch for the power, instead they did it because the bike started better. They have then gone on to increase (by other methods) the BHP wildly.
Aside from better starting, if you simply switch to twin plugs you will probably not see any increase in power. If you switch to twin plugs and set your timing to 15-19 degrees, you may find some HP. Retarding the timing quickly increases the compression and delivers the spark much closer to pushing the piston down when it is headed down than having the spark slow down the piston on its way up. It makes life easier for the big end also.
I set my timing on the dyno for maximum power. I then use a degree wheel to see where it is, so I can set it there where re-timing. If I have an advance mechanism or electronic ignition, I check with a strobe to determine if the advance is working and what it is doing under power and at idle.
David
I don't think that is the way to asses the value of twin plugs. I have had several racers say they did not switch for the power, instead they did it because the bike started better. They have then gone on to increase (by other methods) the BHP wildly.
Aside from better starting, if you simply switch to twin plugs you will probably not see any increase in power. If you switch to twin plugs and set your timing to 15-19 degrees, you may find some HP. Retarding the timing quickly increases the compression and delivers the spark much closer to pushing the piston down when it is headed down than having the spark slow down the piston on its way up. It makes life easier for the big end also.
I set my timing on the dyno for maximum power. I then use a degree wheel to see where it is, so I can set it there where re-timing. If I have an advance mechanism or electronic ignition, I check with a strobe to determine if the advance is working and what it is doing under power and at idle.
David
I think the comet got to about 24 degrees on twin plugs and a little more on single but the HP and toque curves were about the same
So for this season I was going to look at the head architecture to see if that could be improved as something was affecting things.
However lack of a championship for the 48 class n the UK took the wind out of us so the racing comet is sidelined for now if we could find the money we might reconfigure for up to 63 class but that's a big ask or the ACU could pull out of sponsorship
So for this season I was going to look at the head architecture to see if that could be improved as something was affecting things.
However lack of a championship for the 48 class n the UK took the wind out of us so the racing comet is sidelined for now if we could find the money we might reconfigure for up to 63 class but that's a big ask or the ACU could pull out of sponsorship
I think the twin plug system suits squish band head designs over stock hemi heads, and especially on an engine with a larger bore where the flame front has to travel further.
That was the direction of my thoughts especially after photos were posted here of some pictures of squish head undersides.
I actually wonder if the opposite is true, we ran a pair of otherwise identical 1150 twins (90 bore with squish heads and 9:1) on the same day on the dyno even to the point of using the same carbs. there was little or no measurable difference in power , just the twin plugged engine ran best with 5 degrees less advance. As the squish heads and pistons concentrate the combustion volume and create turbulence for better charge mixing the reason we always ran twin plugs in the race engines was belt and braces in case of a plug fouling. This had been a perennial problem before we developed pistons with better ring sealing and improved valve guides. There could be more advantage to twin plugs with poorly shaped chambers. The use of twin plugs is normal in piston engine aircraft with double redundant ignition. These normally have low compression and relatively large bores compared to any Vincent as well as being limited to under 4000 rpm. The standard pre flight involves checking the "mag drop" when switching between one, two or both mags, there is normally a small reduction in rpm when on one mag.
Well we can talk about electronics and ignition curves and loose coils and degrees BTDC but I just had to retime a Comet with a standard Mag as I have BTH on my other bikes the faffing about with feeler guages and exact opening points of the contacts and worst of all holding the finally arived at settings while you gingerly do up the big nut hoping the taper doesnt slip..... It all came back to me that rod locking is worth any side hassel what a master stroke I am saving up for another BTH
You can lock up a standard mag, not tightly though, remove the earth brush holder and brush, get a 5/16 BSF bolt and smooth the end off and screw in until it nips the armature, DO NOT USE A SPANNER, FINGERS ONLY, this will hold the armature in place until you tap the drive gear on.