ignition timing

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Qside

Qside

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Some background info: I have a 68 commando. It came as a project so I dont know what was done previously. I am still assembling the bike so I havent tried to start it. I put a boyer ignition in it . The stator and rotor are new lucas parts. I am setting the ignition to 31 degrees advanced.

Here is my question. Could the ignition degree scale in the primary cover be off by 10 degrees? This is what i did: I found TDC using a piston stop. Then I measured 31 degrees advanced. I marked the stator. Then I put on the primary cover and check my mark against the primary protractor scale. It was off by 10-12 degrees. I rechecked this 2-3 times. The primary cover fits and looks like the correct one for the model, but I cant be sure that is the original cover.

My research on access norton site found mention of the scale being off, but most the time, the variation is only reported as just a few degrees. Any ideas would be helpful.
 
How are you using a piston stop to determine TDC?
How did you measure 31 degrees advance?


Some details here would help as I really doubt the ignition timing placard is off by 10-12 degrees.
 
I have 2 commandos, just get it close and back it off till it doesn’t kick back. Then your dead on. Forget the marks.
The re-tard is the one on the kicker
 
Mwood7800 said:
I have 2 commandos, just get it close and back it off till it doesn’t kick back. Then your dead on. Forget the marks.
The re-tard is the one on the kicker
Click to expand...

Mmm ??

One thing I learnt racing was that what might work on the street lasts 10 mins before it blows up the track. This might work riding gently on the street if your lucky. Then again it might not.

Especially if your using ignition where the cylinders are timed independently. Run an engine hard at full throttle for 10 minutes with ignition set like this and probably things are not going to end well.

I got my 1956 500 Dommie up to 52 bhp rear wheel. Much of that is just by blueprinting the bike and getting all settings perfectly. Then it will really fly and be totally reliable.

Answering the OP.

I guess you found TDC by setting a piston stop in the spark plug hole and rotating GENTLY back and forward 360 to each side of TDC until you found the mid point ?

Then you marked the rotor at TDC plus measuring back with a protractor to get 31 deg? But you said stator in your post correct?

If you think about it the protractor on the primary cover can actually be mounted anywhere so long as it is offset the 31deg from the corresponding TDC position.

Think of it like a wire pointer when you use a degree disc. The absolute position of the wire pointer at TDC on the degree disc when the engine is at TDC can be anywhere so long as you get the relative positions correct. Of course most people set the disc when the motor is at TDC so the TDC mark at the top of the disc. Its a lot easier to visualise the piston position that way.

But it doesnt have to be like that.

Is the 31 deg relative mark on the primary case protractor set with respect to engine TDC as if the rotor were a disc mounted TDC at the top ? Im not sure it is ??

Id go back and check your method. I think you may have one step missing in the logic.

Messing around with timing getting it perfectly correct can be a lot more challenging than you originally envisage. :-)
 
ok I measured TDC by using a piston stop, rotate the engine forwards and backwards and then I split the difference. (small screw driver in the spark plug hole to see that the piston was in fact at the top of its travel. Then I used a degree wheel to measure back 31 degrees. I marked that on the stator . I rotate the rotor to the 31 degree mark on the stator. Without moving the stator, I then put the primary cover back on, looked through the inspection hole and noted that the rotor was still at the mark I made on the stator and on the scale that is on the primary was at 20 deg adv.
I must be doing something wrong?
 
You could have an atlas crank (or drive cheek) with the rotor key at a different position ........it happens to me !
 
Remember - since you can make the TDC mark anywhere on the rotor, depending on how you aligned the pointer, that mark, or any subsequent mark, may not align at all with the scale on the primary cover. SO...after you find TDC,
L.A.B. said:
The scribed line on the raised pad should be your rotor reference mark.
Click to expand...

Yep. When you have located TDC using the degree wheel/piston stop, reposition the degree wheel so that the rotor's scribed TDC mark indicates TDC on the degree wheel. Now make a mark on the rotor 32 degrees BTDC (if that's your choice - you could choose any number of degrees that are on the sale). Reinstall the primary cover. That mark should align with the 32 degree mark on the scale. If it doesn't, that's the amount of error in the scale. Note that the primary cover itself can probably shift a bit either way as you mount it due to slop in the alignment pins and introduce a degree or two of error. So if that's the case, be sure you shift the primary cover to the same position every time you remove/remount it.

Re timing/kickback...It was a very common technique in the old days to advance timing until you got some pinging on acceleration and then back off two degrees. You can do it better on a dyno, of course, setting the advance to the point where the most power is made. After using either method, you note where the timing mark aligns and, from then on, set the timing to whatever that setting is. The one thing to watch using these methods is that you are optimizing for whatever fuel you are using. So if you are using 93 (US) for that procedure then you can't put 87 in there and run the bike the same way! ;)

Also, you cannot ASSUME that whatever timing you came up with will work properly on a different engine, even if they are "identical."
 
Last edited:
This is an early commando so it could have an atlas crank... plus who knows what changes were made in the past 50 years by previous owners.
I am using the scribed line as my 0 degree reference point for TDC.

Kommando's recommendation makes sense to me. BY using his recommendation, it would at least make the scale on the primary cover usable for dynamic testing.

I have built 40-50 bikes over the years. I have set the timing many times. I am second guessing myself because the scale is so far off. I dont want to ruin the engine.
 
mexico mike:
That is exactly what i originally did... it said my primary scale is off 10-12 degrees. That is what concerned me to start. I just cant figure out how I could be that far off.
 
qside said:
mexico mike:
That is exactly what i originally did... it said my primary scale is off 10-12 degrees. That is what concerned me to start. I just cant figure out how I could be that far off.
Click to expand...

Me neither! :) The ASSUMPTION is that the rotor/crankshaft location is correct. If the woodruff key location on either the crank or the rotor is other than OEM for a Commando, then, of course, the scribe mark/timing scale won't show the correct numbers.
 
here is a stupid question. Since its a new lucas rotor, could it have different markings/scale on the other side? I never really checked... I just put it on the bike.
 
Once you have the ignition set up, check it with a strobe light and degree disc. If you advance the ignition timing without changing the jetting, it can have the same effect as just leaning-off the jetting. You might start burning things.

What I normally do, is to not follow my own advice. I set the timing up as recommended by the maker - without checking it with the strobe, then I adjust the jetting of my carbs to suit it. I then strongly avoid moving the ignition timing.
 
MexicoMike said:
Remember - since you can make the TDC mark anywhere on the rotor, depending on how you aligned the pointer, that mark, or any subsequent mark, may not align at all with the scale on the primary cover.

This is the point you are missing. There is nothing magical any absolute point on the rotor for timing. Its 31 deg relative to the TDC mark you aligned with the pointer that's important.

SO...after you find TDC,

Yep. When you have located TDC using the degree wheel/piston stop, reposition the degree wheel so that the rotor's scribed TDC mark indicates TDC on the degree wheel. Do not move the crank ! Now make a mark on the rotor 32 degrees BTDC (if that's your choice - you could choose any number of degrees that are on the sale). Reinstall the primary cover. That mark should align with the 32 degree mark on the scale. If it doesn't, that's the amount of error in the scale. Note that the primary cover itself can probably shift a bit either way as you mount it due to slop in the alignment pins and introduce a degree or two of error. So if that's the case, be sure you shift the primary cover to the same position every time you remove/remount it.

I agree.

Kommando also got it right. This is probably the simplest procedure and I will use it myself in future.

Remove cover and attach degree wheel, find TDC, then you retard the crank to 31 BTDC, remove degree wheel without moving crank then put the primary cover back on and mark the rotor at 31 BTDC matching the cover scale.
Click to expand...
 
qside said:
here is a stupid question. Since its a new lucas rotor, could it have different markings/scale on the other side? I never really checked... I just put it on the bike.
Click to expand...
Normally they are plain on the inner surface, there are exceptions where for ET ignition there are holes for pegs.
 
qside said:
here is a stupid question. Since its a new lucas rotor, could it have different markings/scale on the other side? I never really checked... I just put it on the bike.
Click to expand...

Yes, it's likely to have six (two sets of three marked 'A' and 'B') timing marks for BSA and Triumph triples on the machined side.

ignition timing



This is the side that should be facing out:
ignition timing
 
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