VH metallic tapping noise at TDC

[will_curry]

As it happens, yes.

[chris.shearwood]

PS: What position of ignition advance does your engine run smoothest at and what was it set to on this video?...I find the fastest and smoothest is just over 1/2- 2/3 from maximum. Advancing the ignition more makes the engine run more harshly and slightly slower?

I'm no expert but I think that pushing the lever to full advance should make the motor run fastest and the lever fully retarded should slow the motor right down. Here is a link to a Youtube video of my NG. When the motor starts I advance the lever fully and then once warmed up a bit bring the lever back to fully retarded near the end of the video.
https://www.youtube.com/watch?v=pmTY6Vl ... H3p0VoVxpW

[ralfpenkert]

Les, you are right.
It's not a quiet engine and i think it will never be one.
Reason of upload this video was to get some comments.
One member mentioned they always sound like one forgot a spanner.
And even Chris Ariel sounds similar. Listen when it just starts running.
However there is not one right advance lever position.
As it affects idle and power it depends where you're riding.
Stop and go needs less advance than riding on a country road.
Ralf

[Les H]

Hi Chris. thanks for replying and showing the You tube link. Yes the ignition advance lever is being turned the correct way. I push it all the way forward and the revs drop to a very slow tick-over. Pulling it back towards me, increases the revs but after about 2/3s of the way to max, there is a peak in revs and the engine then slow slightly when this point is exceeded. I've watched and listened to your video. I have to say at 0:40 the engine produces a clack sound very much like my VH does as you blip the throttle. I can only assume that sound (which I hate) is bad piston slap? This is likely to reduce as the piston heats, it will also be less noisy with the ignition retarded

[chris.shearwood]

Hello Les,

I think there must be something wrong with your magneto set-up. With the normal Lucas magdyno installed the lever on the handlebar should be pulled all the way back towards the rider to fully retard the ignition timing and, when pushed fully forward towards the front of the bike, fully advanced timing should be obtained.

Once the motor has been warmed up, and with the transmission in neutral, retarding the lever fully should give a very slow tickover i.e. slow enough to just barely keep the motor running. Pushing the lever forwards should speed up the motor with the fastest speed obtained when the lever is fully forward.

I once had a problem with my VH engine not running when the ignition was fully advanced. It turned out that when the points assembly was pushed onto the end of the mag armature shaft and before tightening the screw there was about 20 degrees rotation possible of the points assembly vis a vis the armature shaft (see the poorly drawn arrow in the photo). I found holding the points assembly as far CCW as possible and then tightening the screw, enabled the motor to run correctly. If the points assembly was completely CW it seemed that the points opening position was out of the range of the maximum magnetic flux of the magneto and so gave a poor or no spark. The photo shows roughly the position of the points at maximum magnetic flux.

[Les H]

Hi Chris. I think what causes a lot of confusion is that different advance-retard levers work differently. The old ones PULLED the cable when you pushed the lever forward...but the the later ones PULLED the cable when you pulled the lever towards you. The action of pulling the cable advances the ignition by turning the magneto cam Anti-clockwise when facing the points assembly. As the magneto rotates clockwise (when facing the points) if the cam is rotated anti-clockwise, it will open the points earlier, which is the same as saying the ignition has been advanced....So, pulling the cable advances the ignition, whether the lever moves forwards or backwards.....As regards my engine slowing after full advance is set, it might indicate a problem but it might be normal too . If the firing is set off too early for the piston speed, it will start to push the piston back simply because there is too much time for it to do so. At higher revs, there is LESS TIME for the gas expansion to develop fully and maximum pressure will occur when the piston has reached TDC and beyond which is optimum. I did re-set the timing with lots of care so I was interested if anyone else has experienced this. The other possibility (unknown as yet to me) is that the engine may well have a higher comp ration piston fitted. This might cause the observed slowing when used with a setting optimised for low CR pistons, simply because higher CR's cause a faster burn rate and require less ignition advance ideally at low RPMs.

[will_curry]

The more the mixture is compressed the faster it will burn but you need to bear in mind
that just because the engine has a 9:1 piston fitted doesn't mean that the compression
in the cylinder is anything like 9:1 unless the throttle is fully open. At tickover the effective
compression will be considerably smaller.

[Les H]

Hi Will. I agree but relatively speaking, at any given revs, the flame front is likely to be faster with a high compression engine compared to a low compression version...even at tick-over and only partial cylinder filling. The flame front has a finite speed so time is taken for the full pressure of the burn to develop. If there is too much time (ignition advance) given before TDC then there will be a point when the build up of pressure starts to push back on the rising piston and this will obviously slow the engines rev's. On a higher comp engine this is likely to occur earlier so less ignition advance, certainly at tick-over....By the way, I don't know if I DO have a Hi-Comp piston. I am heartened by the fact that some posts back, you said your engine similarly did not like ticking over on full advance. This has comforted me, but also raised one other question please. If you ride these bikes in town, you must have to set the ignition at around mid setting?...Otherwise you would be advancing and retarding it every few seconds or minutes of riding?

[will_curry]

The two high compression engines both require more work with the ignition
lever than the lower compression engines to get the best out of them.

I know that I generally make much more use of the ignition lever than most
riders who manage with full advance at all speeds and throttle openings.

A quick look down the plug hole might give some idea. The piston in one
engine is distinctly dished whereas the high compression pistons are
obviously domed. A quick look at the DraganFly website will give you
some idea.

[Les H]

Thanks Will. When I can be bothered I will check. At the moment I am doing some other tidying work to it and also doing lots of gardening...which I enjoy but not as much as the bikes...but it has to be done.