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Rocker question - round heads

J

jcd06

Just got it firing!
Joined
Jun 6, 2014
Messages
5
Hi all,

The idea is to build a setup allowing grinding of the rocker tip face.
I did some measurements on 5 rockers to find out some of the dimensions.
What I want to know are the radius of the tip face touching the valve stem, and the distance between the center of this radius and the center of the rocker shaft.
These are the results:

Radius of the part touching the valve stem
6.290
6.351
6.385
6.301
6.343
(Average 6.334)

Distance between centers
36.258
36.439
36.332
36.248
36.175
(Average 36.2904)

I don't know what to think about the spread on these results.
From a purely mechanical point of view it looks large but on the other hand I've heard about much higher differences on rockers of Dnepr engines.
Are these dimensions somewhere documented?
All comments are welcome.
 
Many years ago, Stan Fridus was researching to make a roller tip system for the rockers. He gave up for a good reason.
 
john zibell said:
Many years ago, Stan Fridus was researching to make a roller tip system for the rockers. He gave up for a good reason.
Click to expand...
It's been done, they're offered for sale on occasion.

I think what jcd06 is trying to do is make a jig to hold the rocker arm securely, and in the proper position, in order to reface the tip. Having a "divot" worn into the tip is very common on older engines. I've seen machine shops just "freehand" grind them on a valve grinding machine or even a belt sander!
 
jcd06 said:
Hi all,

The idea is to build a setup allowing grinding of the rocker tip face.
I did some measurements on 5 rockers to find out some of the dimensions.
What I want to know are the radius of the tip face touching the valve stem, and the distance between the center of this radius and the center of the rocker shaft.
These are the results:

Radius of the part touching the valve stem
6.290
6.351
6.385
6.301
6.343
(Average 6.334)

Distance between centers
36.258
36.439
36.332
36.248
36.175
(Average 36.2904)

I don't know what to think about the spread on these results.
From a purely mechanical point of view it looks large but on the other hand I've heard about much higher differences on rockers of Dnepr engines.
Are these dimensions somewhere documented?
All comments are welcome.
Click to expand...
I would leave Dnepr out as a bar for precision… even a low bar…
 
So I guess I am still not understanding what the OP is trying to accomplish here.

It is clearly “lipstick on a pig” to me.

What possible gain is expected from a low lift cam vintage Moto Guzzi pushrod engine by spending all of this time, energy, and money on corrected geometry rocker arms?

Nothing. That is what you will get of significance from these machinations. Nothing.

It’s like putting hand laid carbon fiber wheels on a V-11EV. Sure, you can do anything, but why and at what cost/benefit?
 
scottmastrocinque said:
So I guess I am still not understanding what the OP is trying to accomplish here.
Click to expand...

As I wrote above: "I think what jcd06 is trying to do is make a jig to hold the rocker arm securely, and in the proper position, in order to reface the tip. Having a "divot" worn into the tip is very common on older engines. I've seen machine shops just "freehand" grind them on a valve grinding machine or even a belt sander!"

The roller rocker thread drift had nothing to do with him.
 
I guess Charlie but still… pig lipstick.

If I absolutely had too, I would do the exact same thing! I would probably just give it a few hand passes across a lapping stone. Nothing more and never give it a second thought.

The rocker surface that interacts with the valve stem just isn’t a critical point requiring this type of precision and detailing.

As long as the feeler gauge gap checks out, I’d run it and forget about it.

Why do limited “blueprinting” on this one item?

It won’t amount to a hill of beans either way.
 
I would assume that a deeper divot in the rocker arm may interfere with measuring with a feeler gauge…
Otherwise yes… Not worth a second thought!
 
You could have a 2 mm deep hole in the center of the rocker arm surface that rides on the valve head, and the engine would still run just fine. The high spot(s) will push against the valve stem and open the valves just fine. Is it perfect? No, but perfection isn’t required here and gains you nothing.

If the mating surfaces were 100% perfect and geometrically aligned, no noticeable difference would be detected.
 
Sorry for my late reply and thanks for your answers.

Amboman said:
I think what jcd06 is trying to do is make a jig to hold the rocker arm securely, and in the proper position, in order to reface the tip.
Click to expand...
Indeed.

scottmastrocinque said:
Nothing. That is what you will get of significance from these machinations. Nothing.
Click to expand...
Then don't.

I will post a photo as soon as the setup is ready. That could take a while...

A German company is offering a rocker arm refurbishing service, which includes grinding of the tip.
It's not the kind of machine shop grinding freehand or on a belt sander.
 
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