Series ‘A’ Valves

kettlrj

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The thread on series A valves is 11/32" x 32 TPI. I would like to purchase a tap & die set. Does anyone know of where they can be obtained?
 

Robert Watson

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vibrac

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Nope beats any of Tracy tools offerings its the 11/32 that does it. (I can see it its almost 9mm but I wont recommend sacrilege)
 

kettlrj

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Many thanks Robert. I mailed them to ask if the thread form is Whit or UN but have not had a reply.
I will go ahead and order any way as the difference in thread form is minute.
 

Robert Watson

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It is UN according to what I saw, but as my good friend and world class machinist has pointed out to me, the thread won't care about a 2.5 degree difference on the angle, and if you are making new threaded collars as well, then you can make them to match!
 

oexing

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What is the idea about threads on these valves unlike split collets ? I do know nothing about series A engines, any photos for me to learn more ?
Actually I would be a little scared to cut threads into the valve stem - or so I imagine from this posting.

Vic
 

kettlrj

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Hi Vic,
The series A engine is fitted with hairpin valve springs that fit under a retainer that screws on to the top of the valve, which in turn is locked in place by a locking washer that fits over the square end of the valve. Have a look on the web for an exploded view of the A engine to see how it all fits together.
Regards Richard.
 

oexing

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Hi Richard,
thanks, I got some more clue now about that silly design - but no idea why they decided on this solution to a problem that does not exist on other bikes. Frankly, I would not want to copy this and machine threads onto valve stems to have all things original. I did a mod on a prewar Guzzi with same type of valve springs but used optimal valve cotters of the three grooves type to enable the valves to rotate a bit . The machined bit is aluminium and no threads or locking plates are necessary so oscillating weight is minimized - which will be milder on cam lobes.
The adjusting screw has a ball end plus its cup, no wear.

Vic

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