modifying the cam dwell

[blockmanjohn]

Hi, I need to modify the dwell on a cam on my Scuderi cycle engine that I built. I need to have the intake valve stay open for about 10 degrees longer so I would like to build up the lobe a bit. I no longer have access to a milling machine or lathe so making a new cam is not an option.
I was thinking of using a small piece of turcite and grinding to the final shape. What do you think? I have no experience with this material so this is my best guess.
If any one has a better idea, or can offer any help with using turcite for this purpose I would greatly appreciate it.

Thank you in advance, John.

 

[Lloyd-ss]

Do you have a closeup picture of the cam and follower?

 

[blockmanjohn]

The photo shows the cam in place. It is the one closest to the sprocket. I am trying to build up the lobe with some JB weld. I am pretty sure it will not hold up over time, but I plan to file it down to the point where the dwell is correct just to get an idea of the correct profile that I will ultimately need.

The drawing shows the cam, and the arrow points the the area that needs to be built up.

I hope this helps, thanks, John.

 

[Lloyd-ss]

Just a couple of thoughts.
1)If the springs at the rockers are as light as they look, the followers aren't putting too much force on the cam. Also, with the followers contacting the bottom of the cam, their additional weight is not added to the force against the cam lobes. So that is a good thing. Less force and wear on the lobe.
2)If your JB weld is applied to the trailing side of the lobe, it is more likely to hold up than if it is on the leading side of the lobe. The leading ramp take the bulk of the force.
3) Because the cam is removable, and because the rocker is adjustable, you could carefully re-grind the cam it by hand to increase the dwell. Here is how. Grind the 8.5mm R of the cam down to 8.0mm, but do not grind into the existing ramps on either side of the lobe. grind the peak of the lobe down from 9.25mm to 8.75mm. That maintains the 0.75mm lift at the rocker but it also effectively lengthens that 3.0mm approximate dimension at the top of the lobe to maybe 3.7mm, and therefore adds to the 50 degrees dwell. The rocker adjustment screw will take up the lost 0.5mm from the base and tip of the cam.

Number 3 could actually be a permanent fix.
Lloyd
P.S. I could add a sketch of the lobe mod if it doesn't make sense or is unclear. This is actually a standard cam regrinding method.

 

[minh-thanh]

I can't make suggestions , But :
A long time ago, I sharpened the lobes by hand, sharpened with a hand grinder, file and sandpaper, made few lobes. The engine runs quite well, ...just a little skillful and meticulous