Yes, the cam lobe is slightly off center relative to the tappet, the idea
being that this will rotate the tappet. Sometimes it even works. There
have been lots of methods used over the years to make tappets rotate.
AFAIK the most successful has been the tapered cam lobe in combination
with a slightly domed tappet face.
However I think the primary contributor to wear in the XPAG/XPAG setup is
the narrowness of the cam lobes. They need to be much wider to spread the
load over greater surface area.
On Sun, 28 Oct 2001, Robert Grunau wrote:
> I always thought the cam lobe was slightly forward of center on the follower
> so the wiping action as the cam contacted the follower would spin the
> follower. Usually most of the followers will show marks of spinning.
> I never thought this idea of a slight taper on the cam lobe or dome on the
> follower would last very long,
> Bob
> On Sun, 28 Oct 2001, Bullwinkle wrote:
>
> > When a cam is properly ground, there is a slight taper or curvature
> > put onto the lobes to cause the tappets to rotate. If however the cam
> > is worn or improperly ground this doesn't happen. The correct repair
> > is to replace both the cam and the tappets.
>
> The "normal" technique is to put a slight taper on the cam lobes and a
> slight dome on the tappet faces. "Normal" is the key word here.
> I don't know about the replacement cams and tappets currently available,
> but the originals were perfectly flat-faced. Bad design, prone to rapid
> wear.
--
Chip Old 1948 M.G. TC TC6710 XPAG7430 NEMGTR #2271
Cub Hill, Maryland 1962 Triumph TR4 CT3154LO CT3479E
fold@bcpl.net
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