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    • CommentAuthorkamran
    • CommentTimeFeb 19th 2009 edited
    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.
    • CommentAuthordavid
    • CommentTimeFeb 20th 2009
    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
    There is a cam lift calculator over at model engine news that includes the lifter diameter.

    His calc says with your lift base circle and a .5 inch flank your follower needs to be only .150

    If you think the flank radius changes things, change the lift and watch what happens.
    • CommentAuthordavid
    • CommentTimeFeb 20th 2009
    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.
    • CommentAuthorkamran
    • CommentTimeFeb 20th 2009
    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.
    • CommentAuthorjay rich
    • CommentTimeFeb 22nd 2009
    david i know back in the 60s jeep had a over head cam also the had one cam per cylinder bank and steve that is a great calculator ....jay
    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
    • CommentAuthormiller
    • CommentTimeMar 10th 2010
    I personally think that roller lifters are the best because there is very little friction.