02-26-2016, 08:30 AM
Hi Pete
Are you ready have you got the popcorn and a comfy seat.
First I must explain this is for flat sided cam. the lift on my cam is only 2mm so I see no benefit in trying to make a curve in it.
A valve diagram normally shows the overlap in this case 20° and the lead and lag both 45°, but we need to know the time the valve is open here it's 235°.
Now remember this is crank angle so we must halve these figures for the Cam running at 2-1 ratio.
So we will start with the base circle of the cam then draw a vertical line through it this is the position of the cam at TDC, now we know the overlap is 10° for each cam, so half of that is 5°and we put a line in 5° before TDC.
The valve opening period is 235°, half of that is 117.5° OK I am going to forget about the .5 and draw in a line
117° from valve opening. and draw another line half way between the two to show full open position.
Now look at the point where the Opening line meets the base circle and draw a line at 90° this is one flank of the cam,
repeat at the other side, then we only need to put in another circle to give the lift and rub out the bit we don't want.
Repeat for the other side, then measure between the two cam peaks and we get 107°relationship between the cams.
,A quick break for a beer and to do another drawing , Then on to the machining.
Any questions?? Brian.
Are you ready have you got the popcorn and a comfy seat.
First I must explain this is for flat sided cam. the lift on my cam is only 2mm so I see no benefit in trying to make a curve in it.
A valve diagram normally shows the overlap in this case 20° and the lead and lag both 45°, but we need to know the time the valve is open here it's 235°.
Now remember this is crank angle so we must halve these figures for the Cam running at 2-1 ratio.
So we will start with the base circle of the cam then draw a vertical line through it this is the position of the cam at TDC, now we know the overlap is 10° for each cam, so half of that is 5°and we put a line in 5° before TDC.
The valve opening period is 235°, half of that is 117.5° OK I am going to forget about the .5 and draw in a line
117° from valve opening. and draw another line half way between the two to show full open position.
Now look at the point where the Opening line meets the base circle and draw a line at 90° this is one flank of the cam,
repeat at the other side, then we only need to put in another circle to give the lift and rub out the bit we don't want.
Repeat for the other side, then measure between the two cam peaks and we get 107°relationship between the cams.
,A quick break for a beer and to do another drawing , Then on to the machining.
Any questions?? Brian.
