Static vs Dynamic ignition timing

VegeKev · Post by **VegeKev** » Wed Jul 03, 2013 2:19 am

G'day Gurus....

Quick (I hope :rolleyes

question re ignition timing. I've initially static timed (lining up the 'F') but when I put the timing light on her at idle (or very close to), the timing is roughly half way between the 'F' and the full advance(?) double lines '||'..... this is even with the contact base rotated as far as it will go in the retarding direction. At higher revs the timing moves beyond the '||', as you would expect, so I believe I'm getting full advance but at idle its too advanced.
New points (set to 0.35mm)
New advance mechanism
New condenser
the locating knob on the advance mechanism is located correctly

What am I missing?.....

.....or is this normal?

Thanks,
Kev.

Larzfromarz · Post by **Larzfromarz** » Wed Jul 03, 2013 5:29 am

In my opinion if there are worn parts (thinking cam chain and tensioner) the actual timing will be altered in relation to the marks we see. If your contact base is at it's extreme travel in one direction or the other, I'd say you are are either off a tooth or you have stretched chain.
In my opinion if running correctly, valves adjusted and the advance mechanism is working I wouldn't worry too much about dynamic timing.
I'd like to hear the other thoughts....

Smithers · Post by **Smithers** » Wed Jul 03, 2013 7:45 am

I always just set it and run it. I haven't really questioned the built in mechanisms for controlling the advance and what not. Interesting subject though. I've never bothered to put a timing light on any of my bikes. Here is a nice pic I have in the "Honda Benly CA95 Engine Assembly & TIMING" thread.

Larzfromarz · Post by **Larzfromarz** » Wed Jul 03, 2013 7:52 am

Frankly neither have I. Mostly because it gets somewhat messy with the cover off (on the 160). I need to make a "window cover" from a spare cover. It may be less so on the 150...

Interestingly enough I found (but you could make) a small degree wheel. You could and I am planning on, "degreeing" my next build. It won't do much but map valve timing and ignition
timing, but it good to know and understand what's going on vs what the book says ( show wear etc). They make a variable cam gear which would be valuable for proper degreeing of the cam.
I suppose you could also move the drive pin on the cam end to change initial timing but think isn't much room to make 1 or 2 deg changes. Easy fix there is making breaker cams at varing degrees of advance or retard and swapping the little cams, sorry thinking out loud.

VegeKev · Post by **VegeKev** » Wed Jul 03, 2013 4:14 pm

Hey Gents,
Sounds like I am thinking along the same lines, though I came to the conclusion that the cam chain/tensioner shouldn't affect the ignition timing as its all on the crankshaft. I suppose it depends on what you make your benchmark, the crank (and hence piston TDC) or cam (with valve opening/closing).
I'm thinking that if I work from the crankshaft onward, then the marks on the flywheel should be right (as its keyed to the crankshaft), and the locating knob on the advance mechanism should also be right (as its also keyed to the crankshaft via the flywheel).........so long as piston TDC is actually the 'T' mark!, I've got a feeling that I've read in the volumes here somewhere that its not. Which would mean that the 'F' mark is not actually 5 degrees from TDC....which would mean that I'm barking up a non-existent tree

Larz-interesting that u mention a variable cam gear....any idea where I would get one? Be nice to be able to dial the cam in when I get to the rebuild....

Thanks for the input,
Kev.

Larzfromarz · Post by **Larzfromarz** » Wed Jul 03, 2013 4:55 pm

I've only seen one for the 160,305 and 350 from Cappellini via ebay. If handy with a machine shop you could probably modify a stock cam gear setup.

Sam Green · Post by **Sam Green** » Thu Jul 04, 2013 1:47 am

It's a shame that there is no option to make threads sticky in this forum as I have addressed this problem several times.
In a nutshell, if you run out of adjustment on the points backing plate, chances are that the generator cover has not gone on central to the crankshaft.
If you slacken all the screws holding the cover and the ones holding the drive sprocket cover just enough so that you can wiggle them on the screws, you will see just how far out you can be.
It's then a case of experimenting with the cover until you find the adjustment that you need to correct the timing.

Sam.

Sam Green · Post by **Sam Green** » Thu Jul 04, 2013 1:57 am

Off kevin goes to play about with his cover, I wonder how long it will take him.

Sam.

Sam Green · Post by **Sam Green** » Thu Jul 04, 2013 2:46 am

I just got to thinking (I do sometimes)

I saw his light go out and assumed he had seen my post and gone to play with his ignition.

I then got to thinking again (I do that as well sometimes)

it might be beer oclock time in Aus and he might have gone to the PUB.

OH $hit.

VegeKev · Post by **VegeKev** » Thu Jul 04, 2013 3:49 am

Sam!

Ok...OK...hadn't thought that there might be another benchmark

, but you'd better be right making me undo so many screws!

And Ok you may be right....it is actually brew time down under

.....bugger...now it'll hav to wait till t'morrow................

Kev.

ByTheLake · Post by **ByTheLake** » Thu Jul 04, 2013 3:52 am

Sam Green wrote:In a nutshell, if you run out of adjustment on the points backing plate, chances are that the generator cover has not gone on central to the crankshaft.

I also experienced a similar issue before realizing that my point gap was too large (larger dwell angle). Once I got the point gap set correctly, the static timing setting fell within the range of the backing plate's movement.

VegeKev · Post by **VegeKev** » Thu Jul 04, 2013 4:01 am

Hey BTL,
Yep...I'm hearing you. That was the first thing I checked....as I hadn't checked the gap since I installed the new advance mech.. It was actually a bit tight to start with ('bout 0.28mm), but even when I opened it out to 0.35mm it didn't change the timing much.....do you reckon it should have?
I did experiment with the old points, and with a gap of approx. 0.15mm the timing mark 'F' was getting close to where I thought it should be, though the points were sparking like crazy!
Kev

ByTheLake · Post by **ByTheLake** » Thu Jul 04, 2013 4:25 am

Sounds like you did the right thing - the manual says 0.3mm to 0.4mm point gap. Let me "dwell" on this for a few minutes.

VegeKev · Post by **VegeKev** » Mon Jul 08, 2013 1:44 am

A quick follow up....
Re-checked everything (including the engine cover) and found that the amount of movement required to correct the timing was going to be excessive.
Next thought...wonder what revs she's doing at idle?
Next job...set up tacho
Set up tacho and found revs sitting at idle at around 1500rpm. yep bit high but any lower and it would stutter and stop (I actually thought the revs would be lower than that!..surprising)
So I reckon problem I'm seeing is that the advance is already operating as its supposed to come in after 1200rpm...
Next job...work out how to get her idling slower...

...ideas anyone? Probably need to play some more with the new Mikuni VM20 carb that I'm still playing with re its jetting?...though the air screw is sitting at 2 3/4 out...
Nothing like a challenge...

Kev.