E: Engine Radius on Rockers

R

russell hartley

Forum User
Non-VOC Member
Whilst fitting new rocker feed bolts ET100/1 I could see that the rocker was only touching on one side when opening the valve . Upon checking with ET28 fitted in Vee blocks I found that the rockers are between 0.006" and 0.008" out of square to the rocker pin.
As I have the use of a Surface Grinder with a Radius dresser I'm thinking that I should square them up.
Rather than try to measure an old and worn part, can anyone tell me what the Rad should be on the end of the rockers ET25
 
T

timetraveller

Well Known and Active Forum User
VOC Member
This is an interesting point and one in which I think some feedback from the proper engineers on this Forum would be useful. As far as I can tell the radius is about half and inch but some years ago when I was looking at the design of cams, followers etc. I used ACAD to determine this radius. I found that the radius should be the same as the distance from the centre of the pivot pin to the middle of the fork on the rocker, about 1.6". If this is done then the fork end of the rocker imparts a 1:1 movement of the valve in relation to the movement of the pushrod and in addition the whole of the fork base is used as it rotates . However, there is clearly more to this than I understand as it is clear that Vincents deliberately made the decision to go with half an inch radius on the fork and I assume that they knew far more about this than I do. Perhaps one of the pundits on this Forum could explain why this radius is used.
 
greg brillus

greg brillus

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VOC Member
I always wanted to be a Pundit.............:rolleyes:...............I'm guessing it has to do with the rocker having a near one to one ratio, plus perhaps the actual surface area of contact of the faces of the fork verses the area of the stem collar which seam quite a lot higher than a conventional rocker that contacts the very end of a valve stem on most all other engine designs.
 
C

clevtrev

Well Known and Active Forum User
VOC Member
russell hartley said:
Whilst fitting new rocker feed bolts ET100/1 I could see that the rocker was only touching on one side when opening the valve . Upon checking with ET28 fitted in Vee blocks I found that the rockers are between 0.006" and 0.008" out of square to the rocker pin.
As I have the use of a Surface Grinder with a Radius dresser I'm thinking that I should square them up.
Rather than try to measure an old and worn part, can anyone tell me what the Rad should be on the end of the rockers ET25
Click to expand...
That all depends on whether the hole for the feed bolt is square and perpendicular to the valve centreline, and the rocker pin is also true to the bush and the the rocker arm. You might just be the lucky one.
 
Bill Thomas

Bill Thomas

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VOC Member
I have found there is a bit of movement, If you don't tighten the rocker feed bolt, Put a lever under the adjuster part of the arm and lift it a bit, Then do up the feed bolt, That squares it up a bit. Cheers Bill.
 
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