I have a publication from Isky from the 1970's or so that lists all the
cams they made for foreign cars, including five for the TR series Triumphs.
The chart lists cam lift and valve lift. Checking what they used, I get
1.459 as the ratio they used. Not that I trust completely what Isky said,
because I suspect that they weren't all that careful with minutea like this.
Rocker contour makes a difference too, as does the length of the valve
stems and height of rocker stands, because these both change the angle at
which the rocker will be at midpoint of valve lift and its effect of
lengthening or shortening the distance between the shaft and the valve
centerline and the part of the arc that the end of the rocker swings.
But hey, I was also wrong about the number of angels that could dance on
the end of a pin.
At 09:00 PM 1/12/2005, Greg Solow wrote:
>I don't think that is defection of the valve train due to spring pressure. I
>got 1.45: as a rocker ratio when I checked it years ago with light tension
>"checking " springs. The ratio will vary somewhat depending on how your
>rocker arm geometry is set up. The farther away from the rocker shaft the
>contact point between the rocker and the valve stem is, the higher the ratio
>will be because the lever arm length is longer. Raising or lowering the
>rocker shaft (or the end of the valve stem, or regrinding the end of the
>rocker arm and changing the geometry of the arc on the end of the rocker
>arm) will all change the rocker ratio.
> Greg
>Solow
>----- Original Message -----
>From: "Larry Young" <cartravel@pobox.com>
>To: <fot@Autox.Team.Net>
>Sent: Wednesday, January 12, 2005 12:50 PM
>Subject: Re: TR4 rocker ratio
>
>
> > This question was raised a couple weeks ago. I thought is was time for
> > a technical discussion. A couple years ago I decide to measure the
> > rocker ratio. Using a dial indicator and degree wheel, I measured the
> > lift curve at the cam (no rocker assembly). Then I installed the rocker
> > assembly and measured the lift curve at the valve. I took the ratio of
> > the two curves and got the graph at
> > http://home.swbell.net/cartrip/RockerRatio2.gif . I was surprised and
> > confused by the fact that I did not get a horizonatal line. Later I
> > realized I'm looking at compression of the valve train. After measuring
> > the valve springs constant and installed spring pressure, I was able to
> > estimate a valve train stiffness of about 60,000 lb/in. Sounds like a
> > big number, but with 100 lbs of seat pressure (150 lbs at the cam), you
> > get 2.5 thousandths deflection. I guess this sort of thing is common
> > knowlege in mechanical engineering circles, but it was news to me. So,
> > even though the rocker ratio is 1.49 you don't see that much more lift
> > at the valve.
> >
> > EDWARD BARNARD wrote:
> >
> > >My documentation is showing two different numbers for the stock ratio.
>One is 1.49/1 the other is 1.5/1. Hope that is some help. - Ed
> > >
> > >Stutzman <stutzman@adelphia.net> wrote:what is the TR3/4 stock rocker
>ratio? I always thought it was 1.4 but I can't
> > >find it in the manuals.
> > >bruce stutzman
uncle jack
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