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Rocker Shims


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#1 johnv

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Posted 14 May 2020 - 06:43 AM

I have one set of shims under the rocker shaft.. Does it look likes it needs more?

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#2 nicklouse

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Posted 14 May 2020 - 09:22 AM

Measure and work it out.

 

tip should be about half way though it’s travel as it passes the center of the shaft.



#3 johnv

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Posted 14 May 2020 - 10:12 AM

Not an easy thing to measure?



#4 whistler

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Posted 14 May 2020 - 10:53 AM

I thought the shim thickness was to compensate for the amount skimmed off the head and block.



#5 imack

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Posted 14 May 2020 - 11:06 AM

With roller tip rockers you want the roller sweeping the centre line of the valve stem tip, not towards the front or rear of the tip. I guess the same process will work with non roller tip rockers too.
I use engineers blue on the valve tip - you could colour the stem tip with marker pen for the same result.
Refit the rocker gear and turn the engine over several times by hand.
Remove rocker gear and study where the ink/blue is worn off the stem tip.
If wear is towards spark plug side of stem tip remove shims or remove material from base of rocker posts and recheck with ink/blue.
If towards manifold side of stem tip add shims and redo test to check wear position on stem tip.

Edited by imack, 14 May 2020 - 11:07 AM.


#6 johnv

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Posted 14 May 2020 - 11:06 AM

It is Whistler.. I don't know how much is off the block, I could measure the head I guess.
Imack they're not roller tipped?

Edited by johnv, 14 May 2020 - 11:07 AM.


#7 imack

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Posted 14 May 2020 - 11:09 AM

It is Whistler.. I don't know how much is off the block, I could measure the head I guess.
Imack they're not roller tipped?


It should work with non roller tip too, after all you want the pad sweeping the centre line of the valve tip ideally.

#8 Ethel

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Posted 15 May 2020 - 08:16 AM

I think we're talking about 2 different things here. Within reason*, you want the rocker spaced along the rocker shaft so the pad/roller is centred over the valve stem.

 

*you also want the pushrod close to vertical and definitely not coming in to contact with side of its hole.

 

The other thing is you get the maximum lift transferred the rocker when it's perpendicular to the valve & push rod. Some set it up by shimming/miling the rocker posts so that is nearer mid lift to give the best average. I go with the argument that it's best to get the best return as the valves are just opening because that's where they are the biggest restriction to flow. So the ideal would be have the end of the valve stem on the same horizontal line as the centres of the rocker shaft and tappet screw ball.



#9 johnv

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Posted 15 May 2020 - 08:31 AM

Thanks Ethel. I get the first bit, rockers are centred well on the valve stems. Are you saying that at maximum lift the rockers should be, as it were, level? Which would leave them pointing up quite high when the valve was closed

Edited by johnv, 15 May 2020 - 08:32 AM.





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