sizes of rocker arm

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
SPRIDDLER
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Re: sizes of rocker arm

Post by SPRIDDLER »

So there we have it: a '47 (long stroke engine) is 1" and a '55 is 1 1/4". All we need to know now is the year of Stephen's engine to know which of the two ('47 or '55) applies (or another year).

EDIT: Ah, just woken up and spotted that Stephen's is a '54
If a 1" arm is of interest to try (greater valve lift assuming it replaces a 1 1/4" arm and the piston and inlet valve doesn't clash) I'm happy to post one to Stephen to keep if any good.
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Mick D
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Re: sizes of rocker arm

Post by Mick D »

Thanks Pharisee - makes sense now

Regards Mick
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Re: sizes of rocker arm

Post by StephenG80 »

OK -so the flat bit at the end is not a "sign" but is a bit of a red herring and measuring is the only surefire way to identify them. As such I am also confused!!!!! or is the definitive answer as followers :ugeek: :-

" ignore the flat or continuous taper to the nipple, purely go on measurement. A standard G80s inlet, tappet side, rocker arm is 1 &1/4" and a light weight G2 or 5 is 1&1/8" measured from centre of spindle hole to center of the tip of the nipple"

However, that still does not explain Spriddler's tiddler (sorry buddy :rofl: ) at only 1" as shown in his photo above - that would give even more lift than the G2 or G5 as shown in pharisee's 1&1/8" photo above. So, is "Spriddler's Tiddler" from '47 the ultimate G80s rocker arm upgrade? - answers on a post card please. :roll:
StephenG80
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Re: sizes of rocker arm

Post by StephenG80 »

just seen the latest replies - Spriddler - I would be delighted to try a tiddler '47 (that's very kind of you)- however that would be going from a 1&1/4" to a 1" - is that too much (presuming all the clearances are OK) as the exhaust would lifting a lot less?
StephenG80
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Re: sizes of rocker arm

Post by StephenG80 »

I have PM'd you Spriddler - not sure if it sent OK though. Let me know if nothing came through. Thanks
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Pharisee
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Re: sizes of rocker arm

Post by Pharisee »

When it's all assembled, you can't see exactly what the valve rocker arm is doing. Remember, the arms are moving through an arc, it's not a straight 'up and down' movement. Using a 1" 'tiddler' push rod arm MIGHT cause the valve arm to rotate too much and the end of the arm to slip off the end of the valve stem altogether. In which case, it would probably jam the valve open.... not a nice scenario. Some careful checking would be well worth while. :)
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StephenG80
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Re: sizes of rocker arm

Post by StephenG80 »

Thanks Pharisee - yup - its going to need assembling with engineers blue (is it called that ??) on the end of the valve rocker arm and on top of the valve stem, and kicked over a few times to see how far the contact travels across those two components, before any "live" running!. I fully appreciate is not up and down - my brain can't do the math though in terms of the arc and subsequent increase in travel on the vertical plain on the valve end in relation to the 1/4" decrease in length of the tappet side arm. If anyone likes working such things out please do so :-)
Mick D
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Re: sizes of rocker arm

Post by Mick D »

Hi

A quick doodle with CAD shows the standard 1 1/4" / 1 1/2" assembly to increase the push rod movement by 20% at the valve

The 1" / 1 1/2" assembly increases the push rod movement by 50% at the valve.

Don't think I'd be too concerned over the rocker arm departing the valve but a valve piston collision is a definite possibility.

The above calculations are generalisations but should be accurate to around 1%

Regards Mick
StephenG80
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Re: sizes of rocker arm

Post by StephenG80 »

that's very useful Mick - 50% increase - surely that going to cause problems at all sorts of levels from springs having no travel left to clearances! "
Mick D wrote:Hi

A quick doodle with CAD shows the standard 1 1/4" / 1 1/2" %

Regards Mick
Did you mean those ratios? - I think they should have been '1 1/8" to 1 1/4" ' and then ' 1" to 1 1/4" ie the valve side is staying standard at a length of 1 1/4" and the two tappet side variables are either going to be 1 1/8" or 1"

Maybe that 50% is a bit high?
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Re: sizes of rocker arm

Post by Mick D »

Hi

I based my CAD on push rod levers of either 1" or 1 1/4", (Spriddler's and heavyweight), and valve levers of 1 1/2" per Sprid's post.

I believe the values are correct for these conditions.

Regards Mick
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