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bighly, Why sweat rebuilding the dizzy when you can overcome its major faults using the new Pertronix electronic ignition. Just curious---Keoke /ubbthreads/images/graemlins/cool.gif
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From Chris Dimmock
I apologise up front - this is a long and reasonably detailed post. Tried to
post it last night - but it didn't go through.
If you believe that a Pertronix ignitor fixes "everything" relating to wear in
a 35- 50 year old distributor - and want to keep believing that - then delete
this post now - and may you forever remain in Lucas darkness.
This post is about why it is important "WHEN" the spark gets fired (rather
than just 'what' fires the spark) - and is an attempt to explain what problems
an electronic ignition (Pertronix, Lumenition etc) or a dual points
distributor will cure - and the problems they CAN'T cure - and how to cure
those problems. With all the recent posts - I thought documenting this would
help.
Firstly - I'm not anti -Pertronix or anti-electronic ignition - I just want
to explain what I have discovered myself over the past year or so - and
demystify some of this stuff.
Pertronix part number for a positive earth Pertronix for a BJ8 Lucas 25D
distributor is LU 162AP12 - I bought a Pertronix from Aaron Couper at
coupers-cars.com (in the USA) about this time last year:
https://www.coupers-cars.com/Catalog%20Templates/Pertronix%20Units_products.ht
m
It was $US70 plus freight & taxes No commercial interest yaddah yaddah - best
price I could find - and Aaron is a Kiwi (like Mike Salter!) - so he's a good
bloke!.
But before you rush out and buy one - think about this - what problem are you
trying to solve?
Most people buy a Pertronix - and spend their $US70 plus freight (or more) -
basically to compensate for the fact that their 35 - 50 year old distributor
is worn out. Your distributor shaft bearings, shaft, distributor cam etc are
worn - and so the shaft wobbles. The distributor runs at half engine rpm -
you'd expect its bearings to be worn out after 35- 50 years of driving!.
So why not fix the distributor?
By fitting a Pertronix - you eliminate the mechanical actuation of the
mechanical points (and the condensor) - and replace them with a very accurate
electronic 'switch'. The wobbly mechanical shaft now doesn't mechanically open
and close the points - and you don't have to maintain the points. That's one
problem solved - 'how' the spark is fired.
But - what determines WHEN that spark gets fired?. Its your advance curve -
determined by two weights, pivoting on posts, retained by 2 springs - which
spin in and out at different RPMs - and a cam and post which limit the
movement to a 'maximum' advance. How does the wobbly old worn shaft/ bearings/
Cam/ springs and worn spring posts in the distributor decide WHEN to fire the
spark? The same way that it did before you fitted the Pertronix - by just
wobbling around!. You haven't fixed that problem!
So what are the advantage of fitting a Pertronics inside your Lucas
distributor - or fitting a modern twin point distributor instead of your
Lucas?:
1. a pertronix removes shaft/cam wear as a SPARK IGNITION consistency factor
- by changing HOW the spark is fired - by changing from mechanical actuation
of mechanical points, to optical . But it doesn't remove the shaft/cam wear -
or post/pivot wear, lack of spring tension etc - which affects WHEN the spark
is fired - i.e. the advance curve itself. The Mallory twin point - being brand
new - isn't worn - so it also solves the 'wear' problem.
2. you can't get points bounce with a Pertronix - as it is a hall effect
rather than mechanical points. A dual point eg Mallory distributor also cures
points bounce by halving the amount of work each set of points does. Both are
great to extend revs past say 6,400 rpm on a 6 cylinder engine, and past
7,500rpm on a 4 cylinder engine.
3. a pertronix is cheaper (at around $US70) than a full distributor rebuild
with a complete advance curve regraph (at around $US150 - or so) The Mallory
is dearer still - at around $US200 plus you still need to set the advance
curve of the Mallory to match your engine.
4. a much more consistent 15 KV is maintained at eg 6,000 rpm at the spark
plug - whereas points systems reduce KVA at higher rpm. Both Perrtronix and
dual point Mallory will provide this consistency.
A Pertronix DOESN'T address the effect that the wear in the distributor has
on the actual advance curve itself - i.e. the amount of advance an engine
requires at any particular revs. Your worn out old distributor decides that -
and we just ascertained that your motivation to put in a Pertronix was to
compensate for the worn out bearings/ cam/ shaft!!! But you've ignored the
springs, action plate posts, weights and the wear means you no longer have the
advance curve provided 35 - 50 years ago. And lets face it - if you don't have
a standard camshaft grind, and a standard compression ratio - and aren't
running 100 octane RON (NOT AKI - and not MON) leaded fuel (check in your
owners handbook!) - then that curve isn't correct anyway!.
The correct solution to 1. above - to solve BOTH issues - is the old fashioned
'rebuilding your distributor' method! Replace the worn out bearing/ worn
shaft/ action plate posts/pivots. Then regraph to suit your Healey engine.
Regarding 2 and 4. Is points points bbbounce actually a problem? I don't
believe it is with a road going 6 cyl big Healey with a standard crankshaft.
Points
bounce is only a problem on high revving cars - eg 4 cylinder racing sprites,
or Healey 3000's with Denis Welch's steel bottom end - which go regularly
past 7,000 rpm on the track, and get points bounce - which a Pertronics
solves. On a 6 cylinder engine you don't get points bounce with standard
points until around 6,200 - 6,400 rpm - at which time a standard crankshaft
cures the points bounce - by breaking......... Suffice to say - if you intend
to rev your 100/4 over 7,000 rpm - or your 6 cylinder healey over 6,500 rpm
regularly - then get a pertronix or a Mallory dual point.
Personally - on a BJ8 which sees 5,800 rpm regularly - a correctly set up
Lucas distributor is fine - remember - that was the same distributor which
Formula Juniors and Cooper S and Healeys used in International motorsport
during the 1960s!. Its just that todays ones are 35 - 40 years older and need
to be rebuilt!
I'm not knocking Pertronix - I'm keeping the one I have for a Sprite -
Pertronix solves the points bounce issue better than anything else, in a
standard appearance distributor. But it won't 'fix' your advance curve -
which is probably now way off due to the wear in posts / bearings / lack of
spring tension / worn bearings worn distributor cam - And it won't compensate
for the higher performance camshaft you fitted last rebuild. A rebuild , and a
regraph of your distributor to suit your engines specs, however, will.
In Summary -
- If you have a worn out old 80,000 mile old distributor, and change it to a
Pertronics/Lumenition/ electronic actuation system - your car will definitely
run better, and smoother than before you fitted the Pertronix. In fact - the
more worn out your old distributor is - the happier you'll be with the
Pertronix - hence all the positive postings.
- If you put a new (rebuilt to spec) points based Lucas distributor, with a
correct advance curve to suit the cam timing, compression ratio and the fuel
you run in your engine in 2003, into your car - and then tuned your car, reset
your carbs etc - you'll pick up noticeable seat of the pants bhp and get
better fuel economy, and the car will be smoother.
- If you put a new (rebuilt to spec) points based Lucas distributor, with a
correct advance curve etc in your car - drove it and got used to the
improvements - and then removed the points & condensor from your rebuilt
regraphed Lucas distributor - and fitted a pertronix - you would notice no
difference under 6,000 rpm There would be no measurable improvement. NONE. No
additional smoothness etc - no improvements at all - not until you were
revving past 6,000 rpm.
- If you have a worn out old 80,000 mile old distributor, with a Pertronics
fitted - and you got it rebuilt with a correct advance curve to suit the cam
timing, compression ratio and the fuel you run in your engine in 2003 - and
then tuned your car, reset your carbs etc - you'll probably pick up noticeable
bhp and get better fuel economy - and you would never have a points bounce
problem, and you would be able to continue making great BHP over 6,000rpm
(provided your engine was capable of it).
Getting the advance curve set to a sensible specification - for your engine
spec - and for your use of your Healey - and for the fuel you use - makes a
big difference. Ask anyone who has had their advance curve regraphed. If you
can't find someone 'local' to do this - Barry Campbell from the Austin Healey
Owners Club here in Sydney has done this for over 40 other healey people.
Barry has a large commercial Distributor analyser machine - which he has
converted to extremely accurate digital readouts (rather than swinging
needles).
And he understands advance curves and Healey engines - and has done heaps of
dyno and road testing.
And - aside from being a good bloke - Barry is retired and spends a
ridiculous, non commercial, amount of time doing this stuff. Did I mention
that Barry is fastidious ? : ) With the Australian peso - that makes
it pretty affordable (around $US100 - $US190 plus freight of approx $US25 -
depending on whats wrong, what model it is, and what parts/ machining is
required on your one - sometimes he has exchange or outright sale ones -
mostly BJ8 type) to get you distributor as close to 'perfect' as possible.
Barry built the distributor in my BJ8 (actually - he has built me a few -
we've tried several advance curves and done a lot of testing!)
The black & white car now has a 6 cylinder version of the no vacuum advance
Lucas 23D4 - a 23D6 - a Lucas mechanical advance only distributor. Totally
legal in all historic racing. The 23D4 is what the early/mid 1960's mini
cooper S had, and all the works Sprites/ Minis etc - with a fixed plate, no
Vacuum advance...)
So I now have one of the 'mythical' works type Lucas 23D6 distributors (as
fitted to the triple webered DHMCo prepared Sebring/ Lemans 3000's) in my BJ8
- with an advance curve tailored for my engine specs........... and no vacuum
advance. You see - you can't run a standard Healey/ Lucas Vacuum advance with
triple webers on a Healey - but that's another story... And if I ever got a
Dennis Welch steel bottom end - I'd put the Pertronix LU 162AP12 inside
it....
No commercial interest in any of this - yaddah yaddah - just passing on stuff
which may help others.
Best regards
Chris
______________________________________
Chris Dimmock
Sydney Australia
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