[Fot] Tappet talk

[Marx Christian tr4-racing]

Ho Larry,

I just made them dead flat....no dome anymore.
I've measure the cam....flat too, no taper.

So the parts should work fine...

Cheers
Chris


----- Original Message -----
From: "Larry Young" <cartravel at pobox.com>
To: "Marx Christian tr4-racing" <chris at tr4-racing.de>
Sent: Thursday, May 24, 2007 5:13 PM
Subject: Re: [Fot] Tappet talk


> Chris,
> I usually see the tappet dome described as a radius and it is usually
> 50" to 100" (1.27 to 2.54 m).  If you go throught the geometry, then for
> a TR lifter of 0.935" (23.75mm) diameter, the dome for a 50" radius is:
> (0.935)**2/50/8 = 0.0022" (0.056 mm).  Did you intend to write 0.07 mm
> (0.00275")?  If so, your number of 0.00275" would correspond to a radius
> of about 40".  I agree this is probably a bit too much dome or too small
> a radius.  I think you should always have tapered lobes.  It is
> important that the taper be matched to the radius on the lifter, so the
> contact point is not at the edge of the lobe.  I usually specify a taper
> of about 0.0025 in/in.  If you go through the geometry, this taper puts
> the contact point on the lifter at a radius of (0.0025)(50) = 0.125"
> (3.18 mm) from the center for a 50" radius or twice that for a 100"
> radius.  TR cam lobes are about 0.56" (14.2 mm) wide, and are offset
> from the lifter center by about 0.05" (1.3 mm), so this taper should
> work well with a lifter radius of 50" to 100". It seems like it would be
> difficult to do this accurately on a lathe.
> Regards,
> Larry
>
> Marx Christian tr4-racing wrote:
>
> >I want to bring that up again because I have some news about.
> >
> >I've installed a new cam and tappets last year and now some of the tappets
> >don't look good and one is damaged.
> >
> >I had a talk with a famous German cam manufacturer (Schrick) and they say
that
> >tappets should be very slightly domed to handle geometrical imperfections.
You
> >can run flat but it is better to have a dome less than 0.002mm
(0.000079").
> >If the cam has a taper grind then you can have a dome of 0.004mm
(0.000157")
> >
> >The tappets on the market seems to have 0.007mm (0.00275") dome which could
be
> >too much and a cause to cam failures. Depends on the cam if there is a
taper
> >grind on.
> >So I think the better idea is to grind them flat and give them a slight
dome
> >by hand on a lathe with fine sandpaper....
> >
> >Cheers
> >Chris