Twin plugging and other options

ChasF

ChasF

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After the last trip in July I changed the ICU to cure a misfire. Initially the bike seemed to start and run a tiny bit better. We've just returned from a 1000 mile shakedown run having refitted the screen which means I can hear the engine a lot more, I noticed some mild pinking when accelerating but can't really be sure this wasn't there before. I use unleaded 98 fuel.

Concerns about the existing bean can, worn bob weights etc. had me looking at fitting the Motorworks kit with electronic advance which then raised the issue of fitting twin plugs but I've really no idea about the pros and cons.

We're off to Portugal in a couple of weeks which will mean that if I go the twin plug route the work will have to wait untill we get back so I suppose I should check the timing in the meantime and see if it can be adjusted to improve the pinking
 
I went down the twin plug route a few years ago. The problem I had with it was it threw up more issues than it solved.

The only gain I can say I saw was a slightly better tickover. I spent hours messing about with bending ears on the bean can, trying different timing settings but can honestly say there was no improvement.

If I was doing it again I'd put the bike on the dyno first and invest in a better electronic ignition like a silent hectic or a Moorespeed unit before setting it up on the dyno again. After the faffing about I had with a Boyer twin plugged ignition I wouldn't bother with one again.
 
I reckon that unless you are looking at proper performance tuning it (ie for significantly greater power, racing, thrashing the kaks off it) then you absolutley do not need to make it more complicated than it already is. The benefits for normal use are marginal, and not worth changing it - and there is quite a lot of experiance on the net regarding issues getting it set up corrctly. By all means fit a single plug motorworks unit and ICU, set the bike up correctly (carbs etc) and leave it at that.

IMHO that is.
 
The most the bike is going to get in terms of performance enhancement is possibly a set of Moorespeed high comp pistons.

It doesn't seem likely that changing the ICU has affected the timing although I suppose it's possible. I'm fairly sure that the pinking is a recent thing. I've never been happy with the centrifugal advance system although to be fair it's been working fine for the past 27 years, and I was reading favourable reviews of the solid state system offered by Motorworks. So when I looked at these I saw that they also did systems for twin plugs and recalled that twin plugging was used to reduce detonation in high compression engines - I know the GS engine is not high compression but that was my train of thought!

I'll see if I can check the timing this afternoon - never done it before.
 
solidstate100 said:
I reckon that unless you are looking at proper performance tuning it (ie for significantly greater power, racing, thrashing the kaks off it) then you absolutley do not need to make it more complicated than it already is. The benefits for normal use are marginal, and not worth changing it - and there is quite a lot of experiance on the net regarding issues getting it set up corrctly. By all means fit a single plug motorworks unit and ICU, set the bike up correctly (carbs etc) and leave it at that.

IMHO that is.
Click to expand...

+1 not worth the cost or the hassle.
 
I know nothing...:D

But I'd of thought a nice well maintained standard bike was the way to go ?
 
I have had a pair of twin plugged airheads for around 10 years.

The twin plugging was done as a package of improvements by Jim Cray and resulted in bikes that were much nicer to ride than stock.

Twin plugging should result in a bike that is smoother, easier to start, more frugal, which will run a highish compression ration on whatever passes for fuel all around Europe with out protest.

Nowadays there are a number of aftermarket ignition systems available, that have ignition advance curves that are suitable for twin plugged bikes (Sachse, Silent Hektik, etc etc) so you don't have to muck around modifying the Stone Age mechanical A/R unit supplied by Bosch.
It's not a cheap option, what with ignition and new coils required, but on a low compression ratio bike, get someone who knows what they are doing to set the squish band gap, by modifying head and cylinder, would give a useful increase in compression ratio and combined with twin plugging would result in a pretty good engine.
 
Twin plugging is a neat way of carrying around a set of spare plugs. And that's about it.

Plus there's always the possibility of the head cracking from the secondary plug hole if it's not done correctly.
 
There's a good article here http://www.gunsmoke.com/motorcycling/r100gs/dual_plug/ that touches on the frustration of trying to get the ignition right. He was spending big bucks with the experts and it still wasn't right. At least the modern alternatives give you a fighting chance.

I spoke to Richard Moore about twin plugging when I was first thinking of building a moorespeed engine. I was expecting to have to twin plug my engine. Richard said he fully expected to go the twin plug route when he was having his Pistons designed but was told by the designer that there was no need with the piston design being used. I think the results he's getting on single spark speak for themselves.

when I had my previous heads twin plugged there was concern over the possibility of the heads cracking so a small spark plug was fitted (out of a Honda of some sort) this in turn bought up concerns about the heat range of the plug...more hassle.
 
Did my R100 years back.
An expensive solution to a none existent problem.
Robs frustration sums it up. Been there with modifying bean cans etc.
I thought I had got better fuel consumption from it. Trying to justify the hassle and time I guess.
Then remembered that I had fitted new needles and jets. Doh!
 
One train of thought is that if you get the squish correct you dont need twin plugs.
Guys who tuned Manx Nortons and Gold Stars, etc, which had decent squish tried twin plugs and found no benefit whatsoever.
My 1000 cc R80 G/S is twin plugged and goes very well, although I dont think the plugs have much to do with it.
It was done with BMW pistons and if you use the correct ones the squish is correct and you have the benefit of small carbs and valves to give you decent intake velocity too - there was a reason Vincent fitted 28.6 mm carbs to the Black Lightning!
 
Beemerboff said:
One train of thought is that if you get the squish correct you dont need twin plugs.
Guys who tuned Manx Nortons and Gold Stars, etc, which had decent squish tried twin plugs and found no benefit whatsoever.
My 1000 cc R80 G/S is twin plugged and goes very well, although I dont think the plugs have much to do with it.
It was done with BMW pistons and if you use the correct ones the squish is correct and you have the benefit of small carbs and valves to give you decent intake velocity too - there was a reason Vincent fitted 28.6 mm carbs to the Black Lightning!
Click to expand...

"Size aint everything, the speed of the incoming charge matters too!" :D OK, I'll get my coat ...
 
Ducati say...

The Ducati Testastretta DVT is equipped with two sparks whose ignition is managed independently: (1) one is placed at the center of the combustion chamber, the additional one (2) on the external side.

The benefit is to provide at any engine speeds a further more effective twin flame-front that ensures complete and efficient burning (quicker and more complete) of the fuel-air mixture within the combustion chamber across a shorter period of time.

At low engine speeds the two plugs work simultaneously, while at high engine speeds the two plugs are managed independently with a dedicated ignition timing.
 
There are definitely two schools of thought here, and seems with the right pistons and good ignition, one plug is the way to go, especially if going for more performance. On the flip side, I had my compression raised and heads twin plugged by Jim Cray and it has run perfectly since, and that was about 3 years ago. He modified the bean can and gave me the dyna coils and plugs with timing instructions. Couldn't be easier.

So whilst twin plugged heads may seem old school to some, there may well still be a place for them. BTW Jim Cray also said, if you buy an R1100S DON'T get the twin plugged model as it is easier to make HP from the single plugged ones........ so he is not just pushing twin plugs as a be all and end all.
 
I dont think Jim Cray does twin plugging unless he does the squish at the same time, which makes sense if it is the squish which makes the difference.
FWIW tightening up the squish will increase the CR , so you will always get an improvement from that , apart from the squish/turbulence and any potential from faster combustion from twin plugs.
There is little benefit in faster combustion for faster's sake, what you want is maximum cylinder pressure when it can be used best, and that is when the conrod is at right angles to the radius or the crankpin, and that can occur when the piston is some way down the barrel.
Rod length helps here , which is why some top tuning kits include different length rods.
 
Beemerboff said:
There is little benefit in faster combustion for faster's sake, what you want is maximum cylinder pressure when it can be used best, and that is when the conrod is at right angles to the radius or the crankpin, and that can occur when the piston is some way down the barrel.
Rod length helps here , which is why some top tuning kits include different length rods.
Click to expand...

Surely maximum cylinder pressure will always occur at TDC. Igniting the plug(s) happens before the piston reaches TDC (and advances with engine RPM) to account for the slight delay in igniting the mixture in the cylinder.

I've always assummed that longer rods are used because the gudgeon pin is closer to the piston crown in some high performance pistons.
 
It is the expanding gas which causes the maximum cylinder pressure, and any pressure at TDC is wasted as the piston is stationary at TDC and the shorter the rod the longer the stationary period.
The short rod also pulls the piston away away from TDC faster when it does start to move so the piston is not around to get the benefit of the increasing pressure or maximum pressure which occurs quite a way down the barrel.
First time I read about this was when BSA were developing the unit construction B44/B50 singles to replace the Gold Stars.
No matter what they did the couldn't get them to pull like a Goldie, until they fitted a 20mm longer rod, the same length as the Goldie one, and the problem was solved.
Smokey Yanic found the same with his V8s, but for some reason few people believed him.
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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