From:Steve Marks
E-Mail:<steve@microdesign.ltd.uk>
Subject:RE: RE: RE: RE: RE: Service Bulletin No 1 - Henderson Timing
Response to:856
Date:Fri Jan 14 04:47:52 2005
Hi Ken, I've emailed a copy of the bulletin direct to you
(if anyone else wants a copy - drop me an email). Yes Ken
you are quite right - the figures referred to were flywheel
rotation not vertcal piston movement(!) The Bulletin
definitely lists 1-1/2" for the DeLuxe - 7/8" for the K -
both set with full retard on the mag. I'd be interested to
hear where your 1-1/4" comes from. I think the reasons for
the discrepancies can be gleaned from the two models'
instruction books as described in my previous posting. I
often seem to ask a question - then go off and find an
answer myself but at least it gets everyone thinking! Thanks
for everyones input. Best regards - Steve 

----- ORIGINAL MESSAGE FOLLOWS -----
Steve , I'm lost regarding your timing , I do not have copy
of buletin number 1 , so can only presume your timing
figures relate to flywheel rotation and not the normal ,
piston position before top dead center (no way 1-1/2"
btdc)anyway the timing on Deluxe is 1-1/4" of flywheel
rotation , not 1-1/2" , which is virtually piston firing AT
TDC on full retard , this is the position I recomend you use
n your K model  all the best and happy new year , Ken

----- ORIGINAL MESSAGE FOLLOWS -----
I'm not much of an expert on "K" models but bear in mind
that upper cylinder design will indirectly effect the timing
 a particular engine. I do not know if their is a
difference in compression ratio between DeLuxe and "K"
models.
                     :John 

----- ORIGINAL MESSAGE FOLLOWS -----
Thanks for you input Dennis. You have a good point and I
follow your thinking - 'if kickback was a problem on the K,
let's retard another 5/8" to make starting easier - after
all an over-retarded engine shouldn't cause any problems'
(bit of overheating perhaps) BUT if the difference between
fully advanced and fully retarded is the same on both models
hat is, the number of degrees moved by the advance/retard
lever on the mag is the same - then surely the 'fully
advaced' timing would be moved by the same 5/8" too. An over
anced engine can definitely cause problems.

The 'Model K Instructions' book is interesting. I quote:
'For general running, the "K" gives best results with three
quarter spark advance. When going full speed with throttle
wide open , advance fully. Retard when motor is under heavy
pull, such as climbing a steep hill, or labouring at low
speed.'
The later 'Instructions for the Care and Operation of the
Deluxe Model Henderson' book says things differently. In
it's riding instructions, it gives a number of situations
when the spark should be retarded and then finishes with
'Otherwise keep spark advanced'. This book refers to both
Simms and Splitdorf Model S magnetos. Is the range of
advance/retard on the two mags the same?

So it would appear that the optimum ignition setting wasn't
at the 'fully advanced' twistgrip position on the model K.
It looks like the rider was expected to know that and select
ood 3/4 position rather than simply winding it 'fully
advanced'. Maybe the average rider wasn't too good at
judging this and so the earlier K model suffered from over
advanced ignition problems? If so, the later setting on the
DeLuxe may have been done to ensure that the rider was
unable to run the engine in such an over advanced condition?
uess the question I'm really asking is - what figure
should I use for my model K? Perhaps use the safer option of
 DeLuxe setting. Any other views welcome. Interesting
eh?....Steve

----- ORIGINAL MESSAGE FOLLOWS -----
a mere detail, like not having a time machine to listen in
on the original engineers conversations c1920 to back my
statements up, let me speculate :) The static timing was
retarded to ease starting. There is less risk of kick back
with less advance. Also, in the presence of the weak spark
produced by the slow (kick speed) rotating mag, a more
compressed mixture will ignite easier and more reliably than
ss dense mixture. What did you guys come up with? 
Dennis

----- ORIGINAL MESSAGE FOLLOWS -----
Hi Guys - happy new year to you all.
So there I was, putting my engine together taking note of
the contents of 'Service Bulletin No 1' dated Jan.20-1922
and headed 'Henderson Timing'. (If anyone doesn't know what
this is, drop me an email and I'll send a copy.) The
bulletin gives the magneto timing as 1 1/2" BTDC for the
model K but only 7/8" BTDC for the DeLuxe. That's quite a
difference and it got me wondering - what changed in the
engine design to bring about the change in timing? This has
produced some interesting discussion over here but no
conclusive answers so I'd be interested to hear what the
rest of you Hen guys think - thanks - Steve