Piston travel vs crank rotation

Came across this 'tool'. I assume it is only one of many. Can anyone say how accurate it is?

http://john.rushworth.com/Pics/Piston/

looks spot on to me. Gives exactly the same results as formulae from Bell's book.

Yes it is spot on I have done a quick test with it and it is right

Mick

Yes it is spot on I have done a quick test with it and it is right

Mick

How do I calculate timings for an exhaust port which ‘opens’ say, 40mm below the top of the barrel (62 bore and 125 rod). According to the chart this gives a timing of 100 degrees. Do I subtract this 100 from 180 and the double it, ie 80 x 2 =160 degrees exhaust timing?

Hi Jimmie

Yes you are thinking on the right lines to calculate total opening angle for an exhaust port.

I guess you intended to say 62mm stroke rather than 62mm bore?

For a 175 Bantam with 58mm stroke and 125mm rod length then 40mm after tdc is about 105.7 degrees after tdc so the total opening works out at 148.6 deg.

The web page takes no account of any gudeon pin offset but for most pistons its between 0 and 1mm so only makes about 0.1 degrees difference to the opening and closing times and the total opening remains much the same.

Mick

Thanks Mick. Them hard sums are really hard!

Jim