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What kind of thread is this???

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Dadandson

Dadandson

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I need to know the thread of stock valve adjusting screws on a 74 1275 OEM rocker arm. It appears to be a 9/32-26 British Standard Fine Thread. All of my handbooks show this thread is obsolete! Can anyone help? Could it be a M7 X 1.0? Thanks
 
Wow! I know the answer, but can not pull it from my brain. The answer came about as we were discussing the click-adjust tool.

Maybe it will spring back into my head in a minute.
 
OK, I made a call. Apparently, last time we discussed this we never found a proper answer and the person used a "work around".

I doubt it is a metric thread. Are you looking for a tap?
 
Yes. I can purchase a tap, if it is metric, but I would like to confirm thread size first. The .275" major diameter does work to 6.98MM and there is only one thread pitch, 1.0, for 7MM thread. I am engineering and manufacturing, what I hope to be, affordable roller rocker arms for A series motors. I am very close right now. The key to my product would be a "No machine" one for one swap with the stamped rocker arms. No extra parts to buy unless the OEM parts are worn. They even fit under a stock valve cover!
 
Well... right there it is (as you said) BSF 9/32-16.
 
BTW, if you are making custom rockers, what lift ratio are you "aiming" for?
 
My goal is to increase the ratio, maybe 1.2 or 1.3:1, but not to point of having to machine the head for push rod clearance. Remember, I want to install these rocker arms without removing the head. I think that would be the appeal of these.
 
Can't you get almost 1.3 with offset bushings?
 
Offset Bushings? Do you mean an out of concentric bushing in the rocker for the rocker shaft? Sounds like some machining involved.
 
No machining required, but they would need to be precisely placed when pressed into place.
 
I have never seen these before. Question: I have maintained the stock dimension from the center of the rocker shaft to the center or contact point of the roller on the valve. I have found that moving the adjusting screw .100" closer to the fulcrum increases the valve opening by .046". Do these bushings move the rocker .100"?
 
I dunno how much they move the rocker. Call David at APT and ask him. Or contact Hap, he might know.
 
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