Hello all, I need to make tappet lifer and wondering if it is better to go with round head or flat head? The cams have sharp edges so I haven’t file them to round edges so I’m thinking to go with round head tappets? Any advantages or disadvantages? By the way is that a correct terminology to use (round head tappet)?
The flat bottom is fine if you have adaquate flank radius. With a curved flank, the edge of the flat bottom will not dig into the lobe. There is also a minimum diameter for the flat bottom.
If you have a flat flank, you might want to go with a ball end lifter or a roller lifter.
I have been working on a new vertical design, .7 bore with OHV, and worked on cam followers. Lots of drawings rotating the cam a few degrees and see how the parts work together. The first design was one cam with two toggle followers. Next was a cam with flat sides that would be milled. A flat follower would have a corner impacting the flat flank of the cam. This needs a round follower or a roller. Tis design is simplest to make and has a rapid rise. As I look at it there seem to be a lot of side forces as well. I switched to a turned cam with all surfaces curved. I was surprised at how large the surface of the follower needed to be so that it always extended past the curve of the cam. As I changed the radius of the flank the dynamics of the cam and the follower change. My cam is to be made from .500 diameter stock and have a lift of .045 but the followers need to be .220 diameter. My initial sketch had the cams .09 wide and the followers .125 dia. If I had built it, the cam rise would hit the edge of the follower and likely jam or damage one part. If anyone is interested in details let me know
A great site that needs some exploring ->link<- . Here is a link to the calculator Steve mentions ->link<- If you have a favorite site share it and they can be added to the list of links. Thanks Steve.
Thanks all for the info. When you follow a plan none of these are questionable but now that I’m designing my own engine, every piece is questionable, therefore progress is slow.
kamran, if you are interested i can send you [elements of cam design] how to plan and produce simple but good cams, by E.T.WESTBURY, MODELENGINENEWS.ORG/camcalc that STEVE mantioned is excellent to get the tappet dia if you can input the 4 mandatory measurements. contact me at stivs@maltanet.net.