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Strobing a twin

Howard

Well Known and Active Website User
VOC Member
Has anyone used a strobe light on a twin?

I can only think of marking the "mag" pinion, then using a perspex cover with a scale on it.

My next problem is, if this works what will the wasted spark do to the position of the strobe flash(I'm using Pazon)? Will I see the timing mark in 4 places?

H

:confused:
 
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timetraveller

Well Known and Active Website User
VOC Member
One of our French friends came up with a neat gadget to do this. It consists of a CD or DVD disk, suitably engraved with degree markings and fitting on to a special replacement for the big end quill. It is arranged in such a way that the engine can be run, the disk spins and can be strobed and yet oil still is being fed to the big end. Very ingenious and only the relative fragility of the light weight disk make it less than perfect. The wasted spark will be so far away from the correct timing that there will be no reading as the disk in only engraved with degree markers near to the TDC and up to about 40 degrees before TDC. I think that Clevtrev either has them or can put you in touch with the French provider and designer.
 

Howard

Well Known and Active Website User
VOC Member
One of our French friends came up with a neat gadget to do this. It consists of a CD or DVD disk, suitably engraved with degree markings and fitting on to a special replacement for the big end quill. It is arranged in such a way that the engine can be run, the disk spins and can be strobed and yet oil still is being fed to the big end. Very ingenious and only the relative fragility of the light weight disk make it less than perfect. The wasted spark will be so far away from the correct timing that there will be no reading as the disk in only engraved with degree markers near to the TDC and up to about 40 degrees before TDC. I think that Clevtrev either has them or can put you in touch with the French provider and designer.

That sounds interesting. Strangely, I've used a CD on a rod in place of the quill to set the timing (without the engine running). I used Autocad to draw a paper timing disc and glued it on.

H
 

tim welsh

Well Known and Active Website User
Non-VOC Member
I tried strobing my twin a few years ago with a magneto and a perspex cover I made. Couldnt see the marks very well because of the oil splashing onto the cover, and they seemed to be jumping a lot, probably becuse of the ATD "bouncing" at idle. I would go for the French quill system if I were to try again.
Tim
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
I borrowed one of the devices that Francois Grosset makes to allows the engine to be run while a timing disc is mounted in the timing side mainshaft. Francois is very clever and makes some excellent equipment including his electric starter motor kit for twins. I could not get the borrowed mounting device to work satisfactorily. The owner of the device didn't have much success either.
I tried putting marks on the magneto fibre gear and viewed them through a perspex window fixed over the hole in the timing cover. This was not too satisfactory as oil splashes tend to obscure the view and as the gear is small and rotating at half engine speed the resolution of marks is poor.
Convinced that driving from the magneto gear was the way to go I decided to make something to bolt in place of the ET136 timing cover window so that it would:

  1. Seal in the oil splashing around the timing gears.
  2. Extend far enough out from the timing case to: a) clear the exhaust pipe and b) allow a full size timing disc to be fitted so that resolution of the marks was easy to read.
Using the best Heath-Robinson principles I looked through the scrap under the bench and found some tube. On one end I welded a flange and in the other end I put a piece of nylon to serve as a bearing. I cut one end off an old 1/2" drive socket extension. A socket fits on one end to take the drive from the magneto gear fixing nut and the timing disc is fixed to a flange on the outer end.
The contraption seems to work very well. (Does this mean that I will be inducted into the Heath-Robinson hall of fame/shame? ;-))
I bolted on a pointer for the timing disc and set it to TDC on the rear cylinder. I have a BT-H magneto fitted. I slackened the three fixings on the flange a little so that I was able to just turn the magneto with the engine running. With strobe pick-up fitted to the rear cylinder plug lead and the engine running fast enough to get full advance I observed the marks on the degree disc and moved the magneto to get the timing to the figure I required. (Remember that it reads half engine speed. e.g. If you want 34 degrees advance, set it to 17 degrees.)

If you are using a wasted spark ignition system e.g. Boyer, Pazon, etc you will probably see two marks, one for the rear cylinder and another the cylinder angle out of phase as the trigger passes the front cylinder pick-up.
Sorry for the long post. The pictures below may make things more clear.

Timing device 001 (Small).jpg Timing device 003 (Small).jpg

Has anyone used a strobe light on a twin?
I can only think of marking the "mag" pinion, then using a perspex cover with a scale on it.

My next problem is, if this works what will the wasted spark do to the position of the strobe flash(I'm using Pazon)? Will I see the timing mark in 4 places?

:confused:
 
Last edited:

Howard

Well Known and Active Website User
VOC Member
Thanks Tim and Eddy

That's saved me time and effort with the perspex window idea.

Sorry Eddy, no Heath Robinson award from me, it looks like a great idea.

H
 

timetraveller

Well Known and Active Website User
VOC Member
Amazing really. Dick Sherwin came up with something which looks almost identical to BigEd's after we had used the Francois Grosset item. There are pros and cons with both items. Dick broke the engraved CD which was the first type that we used. I can see why Francois used the idea of a CD as they are very light weight and designed to put up with far more revs than our bikes can manage but one does have to be careful while handling it. It also has only a 120 mm diameter so that the engraved scale is quite small. The item like BigEd's can use a larger disk but only goes at half engine speed which again restricts the accuracy with which it can be read. Of the two I preferred Francois' design provided that one can be careful while handling the disk. Initially I was suspicious of driving the disk with the later design from the nut in the center of the ATD and I still have reservation over that.
 
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tim welsh

Well Known and Active Website User
Non-VOC Member
If you use a classic music cd, it works better as its slower and compensates for the engine speed. Anything from the current charts borrowed from your children will not work. :)
 

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