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[scotty]

Has any one set ign timing with boyer ign on static two 500 bullet motors one sets to 32btc the other higher comp sets to 26btc.while the heads are off would like to push piston down bore the correct amount for the fully advanced setting then set boyer at mid point. Any ideas how I convert degrees btc to how many millimeters I have to push piston down bore. Idea is that I can swap motors quickly with no ign timing hassles final check with strobe lamp.

[papasmurf]

You may be sorry you asked:-

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Piston Travel vs. Crank Rotation

d = ((S/2) + L) - (S/2 cos X) - L sin[cos-1 (S/2L sin X)]



S = Stroke (mm)
L = Connecting Rod Length (mm)
X = Crank Angle Before or After TDC (deg)
Note: (L) Rod Length is usually 2 times the (S) Stroke



OR:

HT = (r + c) - (r cos (a)) - SQRT(c^2 - (r sin (a))^2)



r = s/2
dtor = PI/180
a = d x dtor
HT = The height of piston
r = The stroke divided by 2
c = The rod length
a = The crank angle in radians
d = The crank angle in degrees
dtor = Degrees to Radians

[ric]

10° = 0.8mm (recommended 'book' figure when setting the ignition statically)

32° = 8.50mm (fully advanced recommended 'book' figure for when using fuel with an octane rating around 70-75, as available back in the day)

34° = 9.5mm (something a little more appropriate for fuel purchased this century with an octane rating of around 95)

36° = 11.00mm

38° = 12.70mm (1/2")


Hopefully of some use... please ignore the sarcastic bits within the parentheses. I am in no way advocating using any ignition setting other what is printed in the original workshop manual and which has been faithfully reproduced for the last 60+ years.