FV Ignition Timing

[Stylo Seagull]

Stylo,
Do Lambrettas have a timing which varies with engine speed?
If they do, then starting at 17 degrees, what is the actual advance at top engine speed? Would it be near, say, 50 degrees?

Jeremy

As standard, no.... fixed point ignition. There are a few kits and gizmos that will vary ignition timing, but i've never indulged. My totally standard Li150 nipped up on it's maiden voyage with 21 degrees of advance (set via a dti and timing disc whilst building engine and checked with a strobe). Runs ok at 18 though - cooling is pretty marginal too though, so it's a bit of an uphill struggle on all counts.

I was always of the understanding that older, lead containing fuels were of a vastly superior quality to modern day stuff with cleaning additives etc but without the anti knock properties of lead.

Jon

[Stylo Seagull]

when I get some spare time, i'll try to do some timing tests.

Not sure when that'll be though as my trusty 'gulls will be shoving me round the broads piking for the next few months

[Gannet]

Stylo,

2 strokes are obviously quite complex in respect of inlet and outlet 'air' flow - more so I think than 4 strokes - at least I know less about it!

My starting point on this thread was to try to square up and understand the standard stated 23.5 degrees advance compared to my measured 50 ish. This on a Seagull which performs quite satisfactorily.

Petrol. Yes, as you implied, in the past lead improved the anti-knock octane rating. However there are other characteristics of petrol which have changed over the years.
Volatility is one. Old cars suffer from the petrol vapourizing in the fuel lines for example. This won't affect Seagulls as fuel lines are short and underbonnet temperatures are low!
There must be other characteristics that have changed. We need an expert here. My guess is that burn rate/flame speed has changed, although I do not think this will affect Seagulls as their design is not sophisticated and their rpm range is small.

Jeremy

[headdownarseup]

i've just re-read this whole thread and i'm still none the wiser?

i'm also intrigued as to an approximate timing setting on a 102.
done the test with a strobe light as suggested and was horrified to find nearer 55 degrees of advance. (i'm using a wipac magneto, points set to 0'50mm or 20 thou)
this particular 102 i'm working on is definitely not one for the purists among us (if you get my meaning, its more "experimental" shall we say)
anyhow, charles suggests that most if not all seagulls should fire at somewhere around 23.5 degrees of advance.

i've done the same test on my FV, SJM, SJP,LLS, LS,SD,SDP and pretty much all of them are between 40-50 degrees. ( i can borrow more accurate measuring devices if it helps)

JEREMY suggested that there may have been some difference with leaded fuels compared to modern unleaded fuels, with regards to flame speed or what we are trying to understand as "timing".
i would very much like to talk with our irish seaguller to see if there is anything in this "adjustable baseplate". he seems to be a bit of a "racer" on the quiet to me.

i wonder if these questions would be better directed at the racers on this forum?

my initial findings of 50 degrees (probably closer to 45 degrees) would seem to tally with JEREMY'S . was there something in older fuel that enabled engines to run more advance (and possibly cooler temperatures in the cylinder). when using modern unleaded fuel i've noticed that most of my motors seem to take 3-4 pulls from cold after being stood idle for a few months, is this the affect of unleaded fuel and HUGE ignition advance. as already mentioned, seagulls are relatively low compression engines so dont really need high quality fuel or high octane ratings, or high compression.

i'm sure that JEREMY will concur that when the baseplate is moved closer to tdc, then initial starting of the engine is so much easier at aound 30 degrees (ish)
surely, this is closer to what BS designed in the first place? so why then, when we do this simple ignition test, do we find nearly twice these figures at around 50 degrees of advance, and carrying out basic checks to see if the screw is correctly located in the dimple,(which they are on my motors) then 50 odd degrees seems massive by comparison? i dont get it!
i've had a bit of experience at racing 2 stroke minimotos in the past. usually 46cc water cooled engines, that rev to around 16-18000 rpm.
ignition timing on these is around 14-16 degrees btdc, which would roughly tally with a lot of scooter engines that have been previously mentioned earlier in this post.
i appreciate that a scooter/minimoto engine have considerably higher compression, but even so, both types of engine are still running on un leaded fuel and were originally designed with leaded fuel in mind.
so with that in mind, i'm wondering if we should be talking to some old 2 stroke bikers and ask what modifications they've made to timing and the use of unleaded fuel.

there may be something in this after all? think back to when leaded fuel was being phased out and unleaded fuel was brought in. i can remember there was a big uproar with classic car owners saying their cars would never be able to run on the stuff. 6 months to a year later and we begin to see the arrival of "lead substitute" on the shop shelves in all its guises.
whether or not you believe in the properties of these products, there might just be something that we're not noticing yet.
if any of you guys run classic cars these days then i think its fair to assume that the timing has been retarded slightly to cope with modern fuel, or the cylinder head has been reworked with harder valves.

so, why not "re-adjust" the timing on a seagull, its easy to do.(just like a classic car)
the only slightly difficult thing is making a different dimple position, very carefully drill the crankcase with a small drill bit to mark it first, then remove the baseplate completely to finish the drilling process being careful not to go through to the crank bush, so that you now have 2 positions to put the screw into. why not join up the 2 holes effectively making a slot so you can have fully adjustable timing from tdc to 50 degrees (similar to those funky marston jobbies)

i am now going to try and run some tests on this "experimental" 102 i have and see if there is any real difference between the suggested normal setting of 23.5` and what i think is fairly typical on a lot of other seagulls as nearer 40-50`.
i'm going out on my boat later this month so i will report back.
remember this 102 aint your average 102 if you know what i mean


i'd like to know what some of you "secret racers" do with regards to timing. share the info for the rest of us. i mean, it can't be THAT secret, or can it?

jon

[Charles uk]

All the racing Seagull ignition timings that I have measured are in the mid 20's degrees before TDC.

I did run my blue 170 with a 35 BTDC setting by mistake one time, recoil starter, 15 to 20 pulls, a real bastard to start, ran the piston so hot that oil was charing on the underside of the piston crown, this was 5 or 6 years ago when this motor held the speed records in both the Northern & Southern hemispheres.

If your using a modern strobe remember that the dwell angle adjustment must not be in operation to get an accurate reading.

At 50 degrees BTDC I doubt that there is enough temperature & pressure in the combustion chamber to permit flame initiation, & as the combustion duration in a simple 2-stroke (a Seagull) is only of a maximum 50 degrees at peak revs (not dependant of fuel type read G Blair, J Dixon) this would imply that peak cylinder pressure would happen before or at TDC, a situation not conducive to easy starting & smoothish running at all.

The Marston ignition was operating in very different conditions to post 1955 Seagulls, fuel well below 80 octane, so much so that now prewar low performance car owners often add up to 10% paraffin, permissable by law on pre 1947 cars, a heavier flywheel with greater inertia, a longer spark duration & as an optional extra timing that could be adjusted between TDC & about 27 degrees BTDC.

Doesn't modern fuel burn slower than the old stuff?

[Gannet]

Charles, you asked:-

Doesn't modern fuel burn slower than the old stuff?

I think this is the nub of the issue. Although does modern fuel burn faster or slower than 1950's fuel?
We need an authoritive answer on this point.

Burn speed or flame propogation. I have been saying that the amount of ignition advance depends on this characteristic. The slower the burn speed, the more advance required. Of course, the higher the speed, the more advance required. Talking of speed - my FVs idle at about 1200rpm and flat out at about 3500rpm - ie a very small speed range, so a single advance angle is quite sensible.
I am sure that the racers compromise on the best timing for flat out running.

However, following Jon's comments about starting performance, I think the compromise of setting the timing to facilitate good starting is the way to go. Especially with a small FV in a small dinghy, when you have to be in the stern to start it; inevitably results in the exhaust being very deeply immersed, with the potential of poor starting performance. Asking my wife to move her weight as far forward as possible needs careful wording!

Burn speed might or might not be linked to lead - I suspect not. I think that octane rating and the amount of lead are independent of burn speed. (Lead, by chance, was found to be a very good lubricant for valve seats). Lead I do not think is the issue here. But whether it does or doesn't, the burning (!) question is still:-

WHAT ARE BURN SPEEDS OF 1950's FUEL AND MODERN FUEL????????

I have read that compression ratio affects burn speed, but cannot remember in which direction - useful!

Jeremy

[headdownarseup]

hi CHARLES and chums.

interesting you say about the dwell angle, when i was carrying out these "tests", the dwell was set to zero.
HOWEVER, whilst trying to ascertain where ignition was taking place, by moving the dwell setting around i ended up with nearer 55` degrees.
that sounds an awful lot to me? standard "dimple" setting was used.
your 170 i'm guessing would have electronic ignition. is that correct?
how did you alter the timing?

35` would seem to be a lot nearer to where BS had intended to acheive adequate running.
does that mean then that the dimples in the crankcase are purposely drilled in the wrong position? (both for 40 and 100/102 motors) poor quality fuels pre 1950 ish.
could i be on to something here?

from my crude testing at the moment it would seem that by moving the baseplate clockwise by approx. 20 something degrees, starting is sooooo much easier!
hence my interest in trying to create a method of adjustment on the baseplate (similar to the older marstons) to facilitate easier starting and possibly stronger/faster/easier running! does that make sense.

JEREMY
i think your'e right. we need more conclusive evidence if anything like that still exists?
compression will absolutely have an effect on performance/temperature, which may tie in with "flame propogation" as you suggest.
compression i think we discussed this previously by phone as being somewhere in the order of 4 or 5:1 quite low by modern standards i would think.
not sure if say a chainsaw or strimmer engine has higher or lower compression by comparison?
has anyone tried "modifying" a piston to up the compression slightly

anybody tried experimenting with fuel "cocktails" i.e something like an octane booster or oxygen scavenger in their fuel mix?
might be worth a try!

jon

[Charles uk]

When you say compression is 4 or 5 : 1 how are you measuring or calculating that?

The normal convention when discussing Seagull compression is in pounds after 2 or 3 pulls using a screw in compression gauge.

To the best of my knowledge all Seagulls with fixed ignition, have timing that is set in the mid early 20's BTDC & that covers everything from the OA series 1 to the 5R.

All 170's had CDI ignition as did all Seagulls built 1979 or later.

If your old enough to remember "pinking" & what caused it, it becomes obvious that early fuels burnt faster.

I've built racing Seagulls with compression up to just below the point that they will require avgas, about 225 lbs but at these levels & temps would require high silica pistons, that Seagull never manufactured.

All Seagulls were designed to run on "poor" quality fuel, Seagull produced a Kingfisher for the asian market that ran on paraffin after starting on petrol & had identical ignition timing to the petrol version.

[Stelios_Rjk]

All Seagulls were designed to run on "poor" quality fuel, Seagull produced a Kingfisher for the asian market that ran on paraffin after starting on petrol & had identical ignition timing to the petrol version.

That was really interesting!

[Gannet]

I think that we have a communication problem.

Jon, Keith P and myself have checked the timing on various engines and found it to be approx about 50deg BTDC.
Charles says:- To the best of my knowledge all Seagulls with fixed ignition, have timing that is set in the mid early 20's BTDC & that covers everything from the OA series 1 to the 5R.

So, either:-
Jon, keith P and myself have tested odd ball engines or have made a mess of the measuremnt process. Both of course possible.
Or:-
The knowledge that Charles refers to is based on incorrect data.

I think that we should try to sort this point out first, before debating whether:- 1. Is there a problem. 2. Does it matter. 3. Burn rate. 4. Pinking. 5. Starting performance. 6. etc etc etc

[headdownarseup]

CHARLES
crikey- 225lbs of pressure thats massive? how on earth did you manage that?
my very best silver century puts out 80psi as measured by a typical screw in type pressure gague.
maybe i need to phone you one day and try to go through what JEREMY,KEITH and myself have found so far?

i think perhaps the dimple position is purposely drilled in slightly the wrong position to around 40/50 degrees btdc on most 40 or 100/102 motors as the three of us have already found with our motors. (slightly different with SD MODELS as they dont have a dimple)
its quite a simple test to carry out with a strobe light. first you find tdc, then attach a homemade timing disc (i use a knackered villiers cover painted black with lines scribed into it from tdc round to 60/70 degrees)
align the timing disc with tdc and srew down the top nut TIGHT,
start the motor in the tank, attach a 12v power supply to the power leads of your strobe,(i use a spare car battery) and the pick up connecter to the ht lead and hey presto.
ALL of my motors are running around 40 degrees or more with the standard dimple setting.

i dont get it?
i knew that seagulls were a funny breed, but this is just plain weird.
23.5 degrees seems much more correct but then that would mean having to move the baseplate clockwise (as viewed from above) by around 20/25 degrees to acheive the suggested 23.5`.

"older fuel burns faster"
it probably did? (i'd like to try and get a chemical breakdown of ingredients in modern fuel to see what's in the stuff) maybe something to do with what's called "volotile aromatics". its supposed to give petrol its BANG! along with other weird and wonderful chemicals thats probably in there as well?
what can we do to modern fuel to make that burn as fast i wonder.
alter the timing maybe?

as JEREMY suggested, does all this really matter too much, i mean if the engine runs adequatley does it need messing with?
surely in this "retarded" state as most of my motors are, long term use might play havock with points and condensers etc. leading to premature failure of the ignition.

i'm going to hit the books to see if i can understand this any better.

confused (very)

jon

[Charles uk]

Excellent Gannet.

Now explain how you calculated TDC, & where you placed the timing marks & how you came up with the 50 degree figure, how I do the above, is already on here.

So we can work out where the errors are coming from & if they're mine!

To increase the compression ratio you just reduce the combustion chamber volume.

[Collector Inspector]

No one has mentioned a TDC "Indicator" attached to the engine in some form.

To check one day I would find TDC by the forwards and backwards sparkplug hole/piston stop method. Then divide that by 1/2. When that 1/2 measurement would be found that is where you would fit some form of pointer on the engine that aligns with zero on a degree wheel correctly fitted.

Then test.

The "mechanical TDC" has to be found and verified as such. What may look like or feel like TDC can be many degrees away.

B

[Charles uk]

Pointer first Bruce, not last, post a link to where you found that, I can't find it.

[Collector Inspector]

Link?

No Link.

What I stated is what I have always done to find a true TDC?

In that order. Pointer has never been first as it could be "Timing Marks OEM" that may NOT be correct. You have to do it yourself to either confirm OEM or place your own.

Or

I may have not read the thread correctly.............................interesting though.

Once a pointer is installed confirmed and correct.............then check where something fires/opens/closes or do difference for duration etc.

I will just watch this from now on as I was not expecting that reply Charles.

B