Re: TDC Tool (Prezoom)
Posted: Thu May 07, 2015 8:32 am
oldchieft wrote:
Only true for simple harmonic motion, connecting rod angle changes it.
Jon the Chief
As Jon undoubtedly knows a "Scotch yoke" assembly generates true sinusoidal motion. A crank and connecting rod assembly generates a modified motion which approximates sinusoidal motion. The bigger the rod to stroke ratio the closer to sinusoidal motion the piston adopts. At a theoretical infinite rod length you have true sinusoidal motion. However when you are close to TDC or BDC ( within a few degrees) the piston motion is in practice equivalent to sinusoidal regardless of rod ratio as the rod is in practice vertical at these points with no effective rod angle
Interesting mathematics if you do the analysis but not really relevant to the issue.
To get TDC accurate you need to measure either side of TDC where you have a decent vertical movement for a small angular movement and seek the centre point between the two measurements assuming no slop in the various bearings on direction reversal !
cheers
Rohan