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#Post#: 178--------------------------------------------------
Re: The ideal head job
By: Fried Ape Date: November 20, 2014, 6:17 am
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The plug position has a big effect on the burn time of
combustion.
The standard head has the plug offset to one side to clear the
valves. This means the burn starts at one side and has to cross
the head volume. This is one reason why the maximum advance is
so large - to give the mixture time to burn.
Raising the compresion ratio reduces the space in the head and
means that the burn will complete more quickly. However, if this
can only be done by raising the dome of the piston to fill the
hemispherical head, the burn will be compromised because it has
to find its way across a thin space with large amounts of wall
drawing heat away.
Look at a modern 4-valve head - the valves are small and each
pair is set parallel with a narrow angle between the exhaust and
inlet set. The plug is central. The piston crown is wedge shaped
to fill the head space but confine the burn volume to the space
around the plug. The maximum advance is a lot less than for the
New Falcon.
(And for comparison, take a look at the 2-valve head used in the
Honda Jazz 1.4 engine. This has two plugs, as again the use of
two valves prevents the plug being placed in the centre of the
head. Honda also time the ignition to the two plugs separately
so that the engine burns better at low throttle. Clever.)
This modified head design has three benefits: it reduces the
head volume and provides some squish, and it starts the burn at
both sides using two plugs.
The increased compression ratio helps reduce burn time and gets
more torque out.
The (modest) squish helps reduce burn time.
Having two plugs decreases burn time.
Plus the combustion space has a better shape, being more
compact.
The net efffect is that the engine should produce more torque
(=more power), need less ignition advance and (thrashing
excepted) be more economical.
What's not to like?
:-)
#Post#: 179--------------------------------------------------
Re: The ideal head job
By: Fried Ape Date: November 20, 2014, 6:18 am
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Oh, and providing both plugs are of the same heat range, it
shouldn't make any difference that they are different sizes.
Except for carrying spares.
#Post#: 182--------------------------------------------------
Re: The ideal head job
By: banquo Date: November 20, 2014, 7:16 am
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[quote author=Fried Ape link=topic=31.msg179#msg179
date=1416485918]
Oh, and providing both plugs are of the same heat range, it
shouldn't make any difference that they are different sizes.
Except for carrying spares.
[/quote]
Interesting stuff; the carrying of spares was what I was
thinking about, but since having had plug problems 10 years ago,
related to a now replaced coil, I always carry two, thus
ensuring that I never need them... 8)
#Post#: 552--------------------------------------------------
Re: The ideal head job
By: Glorious Span Date: March 10, 2015, 4:13 pm
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[font=arial]
[/font]My own quest for NF engine perfection went as follows.
First I bought a new advance/retard mechanism from an ebay
seller. Then I fitted a Mikuni pumper flat slide carburettor,
slightly larger than the original, and had it mated carefully to
the inlet manifold. I had to cut off and re-weld the throttle
pull upside down due to lack of clearance under the tank.
Everything on the Mikuni is tuneable and I spent a good deal of
time setting up all of the jets properly. A twin-plug head mod
preceded that with some minor gas -flowing in the form of
cleaning up and mild polishing. The valves stayed as they were,
with new springs. My other Falcone came with an original but
very different cam, and the second one's cam was re-ground to
match. I have no idea of the origin of this cam, and cannot find
any information about it, but the cam timing is radically
different to the original. With the static ignition retarded,
the engine now pulls well at very low speeds, from 30kph in top,
but will also rev smoothly and willingly - 80kph in 2nd is no
problem with more to come. This is a bad video, but listen to
the engine pulling in 2nd gear from 4:20. This bike easily
out-accelerates any other NF I have ever met.
HTML https://m.youtube.com/watch?v=v8bT9j_I_3A
#Post#: 553--------------------------------------------------
Re: The ideal head job
By: banquo Date: March 11, 2015, 8:27 am
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Not a bad video at all! it doesn't sound anything like mine,
that's for sure! 8)
#Post#: 1398--------------------------------------------------
Re: The ideal head job
By: leafman60 Date: June 1, 2016, 9:08 am
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Paul, if you are still monitoring this, what are your thoughts
on pistons? I have considered doing a head job similar to the
one you show. I have access to someone very good at this work.
In the process, I am considering a larger piston with better
ring design. What about the BMW pistons? How large can I
safely bore the stock cylinder and to what piston should I
consider fitting. This would also help the compression ratio.
#Post#: 1680--------------------------------------------------
Re: The ideal head job
By: Sigean Date: November 13, 2016, 4:22 am
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Hi,
I came across this thread some months ago, and having suffered
the disastrous effects of a broken exhaust valve in my NF and
the need to repair the damage to the engine, making some
improvements along the way seem to be a good idea. Could you
just confirm that with the cylinder head modification you
describe a standard (flat-topped) piston is run in the engine?
Any advice on the pistons to use? By the way, could you tell me
the make of the valves you used?
Sigean
#Post#: 1681--------------------------------------------------
Re: The ideal head job
By: banquo Date: November 13, 2016, 9:16 am
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I don't think Paul's watching here any more (he didn't reply to
Leafman's thread) and as he no longer owns an NF, I think we've
had all we can ask of him. KenJ has his old bike, and I'm pretty
sure the piston is stock, because the whole point was to reshape
the combustion chamber to a more effective shape, and only a
flat-top pistin will do that. As you can see, the Cylinder Head
Shop did the work, inlcuding the twin-plugging and the valves.
They might have records of what they used, or may recognise the
valves from the photos.
Their valves are UK made:
HTML http://cylinderheadshop.com/valves-made-in-the-uk/
HTML http://cylinderheadshop.com/valves-made-in-the-uk/
#Post#: 1688--------------------------------------------------
Re: The ideal head job
By: Sigean Date: November 17, 2016, 7:51 am
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Many thanks for this. I guessed the piston would be standard
and I need to find one to replace the one with the big hole in
it. But this will have to wait as I need to "clear the decks"
of other on-going projects (not least a Condor engine rebuild)
before tackling the mighty Moto Guzzi.
Kind regards,
Peter
#Post#: 1689--------------------------------------------------
Re: The ideal head job
By: banquo Date: November 17, 2016, 7:58 am
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[quote author=Sigean link=topic=31.msg1688#msg1688
date=1479390712]
(not least a Condor engine rebuild)
[/quote]
HTML https://youtu.be/PPIwFRZXUA4
HTML https://youtu.be/PPIwFRZXUA4
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