Norton Commando 1969 timing issues

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Hi everyone. My friend should send me everything this weekend so next week should be here if it doesn't get stuck on customs. Looking forward to check compression! Thank you for the support!
 
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OP, please complete the loop when you get it running.
Hi Concours
Of course it will be my first priority after all the members support and help! Right now my hands are tied waiting for the parts. The parcel will only be shipped from the UK this next weekend unfortunately. I am taking advantage and order some more bits and bobs, just discovered the seal from the kickstart shaft is leaking. Meanwhile I went through the carbs again to double check the pilot jet hole and it was clear so I was definitely getting fuel. Placed new rear tyre today and previously changed the rear brake shoes. Let's hope compression is good and go from there!
Many thanks!
Cheers
 

motorson

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I did a post called "Linear Piston Travel and Advance Degrees." The chart is below. It is compensated for the spark plug hole angle with the Green numbers. I have a dial indicator that screws into the spark plug hole. The tip is ground into a rounded ball which slides across the piston easily. I find TDC by turning the rear wheel in high gear until the dial indicator is at it's peak. This method allows you to find thirty one degrees or twenty and any in between without taking off the rotor or the primary cover. Just set the piston .362 inches (9.205mm) before top dead center and run around the other side to see if your mark is correct on the primary cover degree markings. I would try it several times to make sure the dial indicator is repeating accurately. If your degree marker is off a little then make a note of how much and keep a record of that so that you can always time that particular Norton accurately with the strobe.

31°= .320" (8.127mm) BTDC (Before Top Dead Center), 0.362” (9.205mm) (compensated for the 62° spark plug hole angle.)
30°= .300" (7.630mm) BTDC, .340” (8.642mm)
29°= .281" (7.147mm) BTDC, .319” (8.095mm)
28°= .263" (6.678mm) BTDC, .298” (7.564mm)
27°= .245" (6.224mm) BTDC, .278” (7.049mm)
26°= .228" (5.784mm) BTDC, .258” (6.551mm)
25°= .211" (5.359mm) BTDC, .239” (6.070mm)
24°= .195" (4.949mm) BTDC, .221” (5.605mm)
23°= .179" (4.554mm) BTDC, .203” (5.158mm)
22°= .164" (4.174mm) BTDC, .186” (4.728mm)
21°= .150" (3.810mm) BTDC, .170” (4.315mm)
20°= .136" (3.462mm) BTDC, .154” (3.921mm)

The figures in GREEN are corrected for the 62° angle of the spark plug hole. When the gauge measures 1 inch of travel the piston will have moved .8829" down so the gauge needs to read more than the actual piston travel to give you the actual piston travel. According to Jim Comstock the crank offset he has measured was only .5 to 1.0mm on 750 and 850 Commando engines which is not much. And, of course, if the piston is domed or dished the dial indicator will be hitting a different part of that dome or dish at the different distances from TDC as it moves across the piston because of the 62° angled spark plug hole.

(One small disclaimer: If you are running rods of any length other than stock then these numbers will not work for your engine. )
 
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I did a post called "Linear Piston Travel and Advance Degrees." The chart is below. It is compensated for the spark plug hole angle with the Green numbers. I have a dial indicator that screws into the spark plug hole. The tip is ground into a rounded ball which slides across the piston easily. I find TDC by turning the rear wheel in high gear until the dial indicator is at it's peak. This method allows you to find thirty one degrees or twenty and any in between without taking off the rotor or the primary cover. Just set the piston .362 inches (9.205mm) before top dead center and run around the other side to see if your mark is correct on the primary cover degree markings. I would try it several times to make sure the dial indicator is repeating accurately. If your degree marker is off a little then make a note of how much and keep a record of that so that you can always time that particular Norton accurately with the strobe.

31°= .320" (8.127mm) BTDC (Before Top Dead Center), 0.362” (9.205mm) (compensated for the 62° spark plug hole angle.)
30°= .300" (7.630mm) BTDC, .340” (8.642mm)
29°= .281" (7.147mm) BTDC, .319” (8.095mm)
28°= .263" (6.678mm) BTDC, .298” (7.564mm)
27°= .245" (6.224mm) BTDC, .278” (7.049mm)
26°= .228" (5.784mm) BTDC, .258” (6.551mm)
25°= .211" (5.359mm) BTDC, .239” (6.070mm)
24°= .195" (4.949mm) BTDC, .221” (5.605mm)
23°= .179" (4.554mm) BTDC, .203” (5.158mm)
22°= .164" (4.174mm) BTDC, .186” (4.728mm)
21°= .150" (3.810mm) BTDC, .170” (4.315mm)
20°= .136" (3.462mm) BTDC, .154” (3.921mm)

The figures in GREEN are corrected for the 62° angle of the spark plug hole. When the gauge measures 1 inch of travel the piston will have moved .8829" down so the gauge needs to read more than the actual piston travel to give you the actual piston travel. According to Jim Comstock the crank offset he has measured was only .5 to 1.0mm on 750 and 850 Commando engines which is not much. And, of course, if the piston is domed or dished the dial indicator will be hitting a different part of that dome or dish at the different distances from TDC as it moves across the piston because of the 62° angled spark plug hole.

(One small disclaimer: If you are running rods of any length other than stock then these numbers will not work for your engine. )
Thanks motorson

The measure I got at 31 degrees from the top of the plug hole to the piston is 46mm
 

Bodger

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I did a post called "Linear Piston Travel and Advance Degrees." The chart is below. It is compensated for the spark plug hole angle with the Green numbers. I have a dial indicator that screws into the spark plug hole. The tip is ground into a rounded ball which slides across the piston easily. I find TDC by turning the rear wheel in high gear until the dial indicator is at it's peak. This method allows you to find thirty one degrees or twenty and any in between without taking off the rotor or the primary cover. Just set the piston .362 inches (9.205mm) before top dead center and run around the other side to see if your mark is correct on the primary cover degree markings. I would try it several times to make sure the dial indicator is repeating accurately. If your degree marker is off a little then make a note of how much and keep a record of that so that you can always time that particular Norton accurately with the strobe.

31°= .320" (8.127mm) BTDC (Before Top Dead Center), 0.362” (9.205mm) (compensated for the 62° spark plug hole angle.)
30°= .300" (7.630mm) BTDC, .340” (8.642mm)
29°= .281" (7.147mm) BTDC, .319” (8.095mm)
28°= .263" (6.678mm) BTDC, .298” (7.564mm)
27°= .245" (6.224mm) BTDC, .278” (7.049mm)
26°= .228" (5.784mm) BTDC, .258” (6.551mm)
25°= .211" (5.359mm) BTDC, .239” (6.070mm)
24°= .195" (4.949mm) BTDC, .221” (5.605mm)
23°= .179" (4.554mm) BTDC, .203” (5.158mm)
22°= .164" (4.174mm) BTDC, .186” (4.728mm)
21°= .150" (3.810mm) BTDC, .170” (4.315mm)
20°= .136" (3.462mm) BTDC, .154” (3.921mm)

The figures in GREEN are corrected for the 62° angle of the spark plug hole. When the gauge measures 1 inch of travel the piston will have moved .8829" down so the gauge needs to read more than the actual piston travel to give you the actual piston travel. According to Jim Comstock the crank offset he has measured was only .5 to 1.0mm on 750 and 850 Commando engines which is not much. And, of course, if the piston is domed or dished the dial indicator will be hitting a different part of that dome or dish at the different distances from TDC as it moves across the piston because of the 62° angled spark plug hole.

(One small disclaimer: If you are running rods of any length other than stock then these numbers will not work for your engine. )
I have a question. How accurately can you find tdc just by watching for where th er dial indicator stops moving, or do you use some other technique? I always thought there was a few degrees of rotation at tdc and bdc where the crank rotates but the piston "floats" without any motion. I also always thought that one reason for using a mechanical stop and a degree wheel to find tdc was that using the stop causes the piston to stop a known number of degrees before and after tdc which can then be found with great accuracy by splitting the difference. I have used a dial indicator instead of a mechanical stop to find a known number of degrees before and after tdc - although I find that method is so fiddely that it has no real advantage over using a mechanical stop. Thanks for your response.
 

motorson

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Thanks motorson

The measure I got at 31 degrees from the top of the plug hole to the piston is 46mm
My method makes no attempt to measure the total distance to the top of the spark plug hole. This would vary a lot depending on compression ratio and gasket thickness for instance.
 

motorson

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I have a question. How accurately can you find tdc just by watching for where th er dial indicator stops moving, or do you use some other technique? I always thought there was a few degrees of rotation at tdc and bdc where the crank rotates but the piston "floats" without any motion. I also always thought that one reason for using a mechanical stop and a degree wheel to find tdc was that using the stop causes the piston to stop a known number of degrees before and after tdc which can then be found with great accuracy by splitting the difference. I have used a dial indicator instead of a mechanical stop to find a known number of degrees before and after tdc - although I find that method is so fiddely that it has no real advantage over using a mechanical stop. Thanks for your response.
I will admit that the dial indicator method is not quite as accurate as the degree wheel with a solid stop and splitting the difference type measurement. If you use a degree wheel then you have to take off the primary cover, find TDC, turn the engine back to somewhere between 20 and 31 degrees BTDC, carefully replace the primary cover and then look to see if the timing mark is correct. Assuming that the engine did not move, this would be the most accurate way to do it.

With my indicator I did not see that theoretical piston float at TDC. What I did see was the indicator turning one way to a point and then going the other way as the crankshaft continued to turn. I did my test in both directions with the same TDC point coming up each time. Then, using the rear wheel in 4th gear, I backed the engine up to somewhere below the specified .362 inches. Turning the rear wheel the other way I came back to .362 BTDC. On one of my primary covers the mark was exactly at 31 degrees. On my other cover, which is on the bike now, the mark was off by one degree.
Dan.
 

texasSlick

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I would be surprised if "true" TDC were more than 1/2 degree from estimated TDC by any of the methods described above, including my simple method as described below.

I use a degree wheel and a spoke in the hole, rocking the engine forwards and backwards, noting the value on the degree wheel where movement of the spoke becomes imperceptible in each direction, then splitting the difference.

A half degree error in setting timing is of no significance.

Slick
 
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