FV Ignition Timing

[Gannet]

While I was fiddling around with FV2682 to try to get it to run properly and thinking that it was an ignition problem, I swapped magneto plates. I noticed that the ident for the rotational location was not on the TDC/BDC centreline. This was true on all four FVs that I looked at; whereas the ident on the two (Villiers) Forty Minus were on the centreline.

Does this mean that the ignition timing is different on the FVs? Or if it is not different, are other parts of the Villiers magneto assembies different and thus are not interchangeable? The magneto plates that are involved are all early 'flangeless' ones.

In respect of the problem with FV2682, the ignition timing problem was a red herring. With advice from Keith P (many thanks), it appears that it is a crankshaft worn bearing problem.

Anyway, if anybody has some comments on FV and FVP(?) ignition system timing and interchangeability, I would be grateful.

Jeremy

[Charles uk]

Perhaps the woodruff key slot in the crankshaft is in a different location as it's a very different crankshaft, FV-SJM therefore different baseplate required.

All Seagulls fire in the low 20's BTDC!

[Gannet]

Thanks Charles,
Does that mean that the baseplates are different?
Or is it possible that the woodruff key slot is in a different position as you suggest and the ident position is also different, so that 20deg was achieved with the baseplate being used for later engines?
Jeremy

[Charles uk]

Sorry never checked.

[Keith.P]

I had a look at a FV and SJP crank and the woodruff key in the the same position on both and as far as the FV/FVP, other then the gearbox the motors are not any difference.

[Gannet]

Thanks for your comments Keith.
The ident location is very very approx. 10 degrees before TDC. This is a significant amount, as Charles L states that the standard ignition timing is 20 degrees TDC.
This offset (10 deg) is present on engines FV1786 to FV 2821.
Keith, is this true of your (later) engines?

Jeremy

[charlesp]

23.5 degrees BTDC if memory serves...

[Charles uk]

The position of the indent is only important when it has a flywheel & points cam attached to it, the cam & the points gap make the final decision on the ignition timing.

[charlesp]

On the earlier versions of the Villiers points box, where the adjustment is by means of a captive screw with locking nut arrangement, the gap was sometimes closed right down to ten thou at the factory.

[Gannet]

Yes, thanks. I understand that the ident position is obviously only one feature which affects the timing. The flywheel and the baseplate assembly being the others. I am ignoring the crankshaft keyway position following Keith's assertion that FV and SJP are the same.
So, to achieve the standard 23.5 degrees with a different (FV to 40-) ident position; something else has to be different. Is it the baseplate or is it the flywheel, or is it both?
Or should FVs points gap be set, as Charles P mentions, to a much smaller value? I am assuming that reducing the points gap reduces the angle before TDC at which the spark occurs - is that right?

Jeremy

[Oyster 49]

The spark happens when the points open, so to change the timing the points arm would need to be moved further out so the points open later, or earlier. I've tried running a seagull with a moveable magneto backplate, and found no real difference to the performance.

[Keith.P]

The bigger the gap the more it will fire BTDC, and the points will stay open longer, the condenser gets charged when the points are shut, the faster the engine runs the farther from BTDC it will fire, as it should.
That's why you have to sometimes shut down the points gap on old motors to keep the points closed as long as possible to get a usable spark.
I think that's right, someone will tell me if it's not.

[Gannet]

Keith, I think we agree that reducing the gap, produces a spark slightly later ie at a smaller angle before TDC.
However, I do not agree that the timing varies with speed. Surely there would need to be another input ie a centrifugal adjustment as on 'old' distributors to achieve this.

Oyster, your comment that the timing doesn't seem to make any real difference is a bit of a conversation stopper. Sounds like I shouldn't worry if on FVs the timing is out. But is this really true? And how far out? Does, say, 10, 15 or 20 degress make any difference? Perhaps I am being too pernickety.

Jeremy

[Oyster 49]

I can only comment of the limited test I did with a 102 and also a FPC. I ran up the canal at half throttle and rotated the magneto back plate each way to see what happend to the engine. Not much to be honest. I did the same with both engines at full throttle and the feeling was that when advanced at full throttle the engine revved a little more, but not much.


Didn't a forum member from Northern Island put a manual advance/retort on a century a while back?

[Gannet]

Thanks Oyster,
That rather indicates that it isn't too critical.
It perhaps helps to answer my original query as to why FVs (at least the five relatively early ones that I looked at) seem to have a different (and larger) advance timing that the later Forty Minus. The answer being - it doesn't matter. I am still very surprised.
Are there any other views or comments?
Jeremy