Author Topic: Setting static ignition timing.  (Read 1608 times)

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Offline Brooklands

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Setting static ignition timing.
« on: December 13, 2011, 09:30:32 PM »
Static timing is when the ignition system is set to produce a spark from rest, at a certain point in the firing cycle. It is usually before Top Dead Centre (BTDC), but may be after, so check your service sheet or handbook first. Often the timing is a physical measurement, say 1/32", and is sometimes also quoted in degrees before  TDC (in this case 1/32" piston rise equates to the crank moving around 12 degrees). 
Timing of 12 degrees BTDC is fine for tickover and low revs, but as revs rise a more advanced igniton is required (up to around  a total 35 degrees) and this is taken care of by either a lever operated cable that physically rotates opening of the points system, automatic weights that rotate the points cam on its shaft (as per C series), or electronic systems. Somewhere around an additional 20/25 degrees is the normal maximum mechanical advance and this falls progressively back to 12 degrees as revs drop away. Too much advance and knocking occurs, too little gives poor performance but possibly accompanied by a good, quiet tickover.
So getting the right static ignition matters as it affects the performance of the engine throughout the rev range. First thing to do is find TDC on the firing or compression stroke. Use the TDC finder for this.
Once the tool is set at TDC hold the spring loaded pin against the piston crown and unwind the running nut 4 flats so that there is a gap between the washers and check the gap with a feeler gauge and adjust if needed to 31 thou (1/32").
Move the piston backwards an inch or so down the bore (the gap will diappear) and then raise the piston again (taking up any play in the distributor drive etc)  until the washers are just about to part. Leave in this position, with the piston now at 1/32" BTDC.
Take off the points cover/cap and see if the points have already opened (firing was advanced) or still closed (retarded). Slacken the base plate screws and rotate the base plate until the points are just opening. You can do this by putting a thin piece of paper/cellophane  between the closed points and pulling it out as the points lose their grip. Or if you made the spark checker tool fit this now, switch the ignition on and rotate the base plate until you see (and hear!) an HT spark, confirming both the points just opening and that your static ignition timing is set to 12 degrees BTDC! Lock the plate screws.
Don't forget to check and reset the points gap whilst you're there.
Also, don't trust the previous owner(s) - my Enfield, purchased new, was not a good starter, kicked & spat back, and ran hot. Initially I thought running-in, weak mixture etc. Static timing was 8 degrees over-advanced from the factory!  Once timing was checked and corrected, it was a pleasure to ride.
Norfolk 'n good!

Offline Brooklands

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Re: Setting static ignition timing.
« Reply #1 on: December 14, 2011, 02:57:04 PM »
And when you've got it 'just so'. punch mark the points base/distributor clamp plate so that you can always re-set to the same marks.
Norfolk 'n good!

Offline Willpower

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Re: Setting static ignition timing.
« Reply #2 on: December 15, 2011, 09:48:48 AM »
I know this is going to be 'frowned' upon, but in my youth I used to race bikes when push starts were the norm, so spot-on ignition timing was one of the critical factors to getting the motor fired up for a fast getaway. 
To eliminate any backlash in the moving parts I used a spark plug body with all the middle removed and fitted a bolt with a locknut so that the bolt length protrudes from the bottom of the plug body by 1/2 inch or so. 

Take the piston to its lowest point and screw the plug/bolt tool into the cylinder head.

The bolt will come into contact with the piston crown twice in this procedure, so slow and gentle as she goes.

Static pointer fitted and timing disc set to zero, the motor is slowly rotated one way until the piston makes firm contact with the bolt and a reading is taken from the disc, then the motor is turned the opposite way until contact with the bolt is made and another reading from the disc is taken.  As hard contact is made in both directions backlash is eliminated.

Split the difference of the remaining degrees and that is tdc.  Remove the plug/bolt tool, take the piston to the split difference figure on the disc and then move the timing disc round so the static pointer is reading zero.

I always use this method for obtaining tdc and have never caused any damage to the pistons.

Raced 1969/73 7R, 500 Manx and a Manx 750 Commando at Croft, Aintree, Silloth, Darley Moor with the odd excursion to Cadwell.
Fylde Coast
1956 C12

Online mike joiner

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Re: Setting static ignition timing.
« Reply #3 on: January 31, 2016, 03:59:13 PM »
Hi there I have just found this write up and notice that the points are shown at the bottom with condensor at top
I thought that this was the other way around ie points at top ?
I am trying to set up a C11G engine and can not get it to spark at the correct time with points at top does it matter ?
If they need to be at the top is there any way of changing the position ?
                    Thanks Mike

Offline chaterlea25

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Re: Setting static ignition timing.
« Reply #4 on: January 31, 2016, 08:50:10 PM »
Hi Mike,
If the auto advance unit is dismantled it is possible to put the cam back on 180deg out
So points plates get turned which ever way that the timing is correct

No one will see it when the cover is on :o
So fit it which ever way the timing is correct or reverse the cam on the ATD