Twin spark plug cylinder head.

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10 inch Terror
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Hi all, I ordered a CNC cylinder head for my RB from Mito Lambretta in November last year. To cut a long story short, it took 9 weeks to arrive for one reason or another. Anyway, they sent me the more expensive twin spark version, plus a few other bits as compensation for the wait. Fair enough I think, so I fit the central plug with no problems, but when I went to fit the plug in the usual position I couldn't get the plug spanner in the hole, as the hole is too small! I used the spark plug socket from my tool kit (as I always have done on any other Lammy cylinder head) So my question is, has anyone else come across this, and is there a spanner out there, that will fit? I Don't really fancy stripping the top end again, and having to grind the hole bigger. Thanks in advance Pete. P.S I have mailed MITO, but I'm still waiting for a reply....
Grumpy225
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Had to look up the head in question.

Looks like they machined the hole too small for a normal wrench, which you are of course running in to now. At this point I'd be on the look out for a thin walled spark plug socket or be willing to pull the head off remachine the hole or find something to plug it up and forget about it. Twin plug heads have always been kind of a smoke and mirrors kind of thing to me. When in doubt just look at what Yamaha did with their head designs.
10 inch Terror
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Thanks for the reply mate. To be honest when they offered me the twin head I wasn't overly keen on it, as it seemed like a faff, having to drill a 2nd hole in the cowling for the extra plug. Anyway, they told me that it ran 20% cooler than a standard head, and if I used a short plug, I didn't need to drill the cowling. I'll have a look at thin walled plug spanners and see if I can find one, I've got one of the MB ones somewhere in my shed, I'll dig that out and try that. Cheers, Pete.
Grumpy225
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20% cooler?

If I remember my motor theory correctly, lower temp = lower power and higher temp = higher power (until it goes bang of course)

Now I could imagine that twin spark should equal more complete combustion but that wouldn't make it run cooler because unburnt fuel is naturally colder than burning fuel.
10 inch Terror
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Low temp = less power? So why water cool cylinders and cylinder heads? The twin spark idea allows you to run a centre plug, if you choose too, nothing more. You simply fit the ht cap to whichever spark plug you are using, and the other plug, is just a 'plug'.
Muppet
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two plugs is moor expensive; just use one in centa :mrgreen:
C’est la vie
Grumpy225
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10 inch Terror wrote:Low temp = less power? So why water cool cylinders and cylinder heads?
So you can make more power without the piston going bang.

The whole reason for WC is so you can run high compression, advanced timing, etc. The power making things that generate more heat than the fan setup can handle. At least that's how understand it
Dryballs
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Aprillia did testing with their gp bikes a few years ago, playing around with bigger radiators etc. they found the cooler things ran the more horsepower it made.

They ended up with radiators so big it ran at 50'C at full race temp

That was on simoncelli's championship winning bike
warts
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I twin plugged my guzzi. Yup, a 4t. The idea was to shorten the flame path - 90mm is quite a long way to go in nth of a second. Worked well, engine ran much cooler, especially in the Alps in summer.
The two plugs were now on opposite sides of the combustion chamber and the two flame fronts travelled towards each other. Once I had adjusted the squish to a fairly tight value, torque went up noticeably.
If I understand 10", there is one plug on the side as per normal, and one in the middle, so not much to gain from shorter flame paths.
Back in the sixties, when the big brit bikes were beginning to be thrashed in competitions like the ISDT by tiny 2t's from eastern Europe, MZ's, CZ's, Jawa's and the like often had twin plugs. The idea being if a plug got fouled you just swapped over. Of course, if one plug fouled, then like as not the other would be too.
Seems in this case you have the option to run either, but a bit of a palaver to swop. As well as the accessibility thing, the shorter burn time would affect timing requirements, so maybe that would need to be worked out too.
Grumpy225
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Dryballs wrote:Aprillia did testing with their gp bikes a few years ago, playing around with bigger radiators etc. they found the cooler things ran the more horsepower it made.

They ended up with radiators so big it ran at 50'C at full race temp

That was on simoncelli's championship winning bike
Not to get too far off topic, if you have a link to that I'd love to read it.

50c is only 122f, not as cold as thought it would be. The GP bike had to be making some serious power compared to its stock equlivent (naturally).
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