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Series ‘A’ Valves


kettlrj

Well Known and Active Website User
VOC Member
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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VOC Member

vibrac

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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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VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

P1060847.JPG

P1060852.JPG
 

Bill Thomas

Well Known and Active Website User
VOC Member
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
Hello Vic, Brother Ron had a few " A " s, I don't remember him having trouble with the Threaded bit of the valves, His trouble was from the B.A., Screws and nuts which stopped the locking plate from undoing,
The Paul Richardson, Vincent book, says to solder the nuts, After tightening, They were always going missing !.
The photo Bruce has shown us, Don't show them well. Cheers Bill.
 

vibrac

Well Known and Active Website User
VOC Member
And they had a nice pair of shovel tongs to fit them in the paddock
back in the day coil springs had a tendency to loose tension if they got too hot and tended to be strong on OHV engines but the hairpin design allowed a lighter spring and kept it away from excess heat
 

oexing

Well Known and Active Website User
VOC Member
Still I don´t see any benefit in that threaded design. I wouldn´t want to cut any threads into the valve stem , provided you got a decent valve steel at all. So with modern material - I wouldn´t accept anything less - you´d have less of a problem to machine a typical recess for standard valve split collets or the three grooves type.
This threaded (dreaded) design seems to me just a fancy idea to be different from other manufacturers but in effect not to your advantage - as happened very often in earlier times when pride in the design offices prevented acceptance of proven solutions.

Vic
 

timetraveller

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VOC Member
This might be sacrilege to the 'A' boys but my first meeting with Peter Gerrish was when we were both conscripts in the RAF and occupying the same dormitory. Peter, was either part way through or had just finished modifying his 'A' head to take later type helical valve springs. As a non 'A' person it looked to be a much better job to me although, of course, non standard. I will now retire to the bunker.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Just trying to think what Harold Pass did, His Morgan three wheeler had an "A" Twin engine with strange valve
fitting. Cheers Bill.
 

kettlrj

Well Known and Active Website User
VOC Member
I think that Harold converted his heads to coil springs. Bob Stafford documented in the past, the use of post war valves. This mod should be in the new book to come out regarding the series 'A' bikes. Maybe the original idea was to be able to vary the spring pressure for some reason by screwing the spring retainer up or down the threads. As far as I know, there is less chance of the valves breaking at the threads than there is of the post war valves breaking at the step where the collar sits.
 

A_HRD

Well Known and Active Website User
VOC Member
I think that Harold converted his heads to coil springs. Bob Stafford documented in the past, the use of post war valves. This mod should be in the new book to come out regarding the series 'A' bikes. Maybe the original idea was to be able to vary the spring pressure for some reason by screwing the spring retainer up or down the threads. As far as I know, there is less chance of the valves breaking at the threads than there is of the post war valves breaking at the step where the collar sits.
Quite right Kettirj; and Bob Stafford's write-up for using postwar valves - but retaining the hairpins for aesthetic reasons - is in "Back to A" on Page 244. Some people went further and modified the heads for post-war springs too.... o_O:eek:

Incidentally, there are two reports, from different parts of the globe, of new Series A hairpin springs breaking in the last few months. I'd like to know whereabouts on the spring they broke; perhaps there's a suspect batch out there somewhere?

Peter B
 

greg brillus

Well Known and Active Website User
VOC Member
The valve spring cap has to screw up tight. It clamps the stem sleeve that bottoms against the step on the valve stem, the hat section at the bottom of this sleeve is what the fork of the rocker rests on. That is why it needs the locking top cap and small screws/nuts to stop the assembly from coming undone. It is similar in action to the post war set up, but more fiddly with more moving parts, that's why those small screws and nuts fall off from vibration and originally locked by securing with solder. That was quite a common method of hardware retention back in those days, you see it in magneto's and generators as well.
 

oexing

Well Known and Active Website User
VOC Member
Well. this thread started with an enquiry about tap and die for reproducing new valve sets for the A. I wonder how far this job has come by now. I´d think there is no good chance to cut decent threads into modern valve stems with simple die sets - provided the material of the stem was a quality I´d accept. So for that reason I´d go for more modern valve collet recesses that you can machine much easier and simplify the whole affair as well , safer too. Keeping the old design would not be my objective. The A series valves have the same stepped stems with double diameters like the postwar types I guess ?

Vic
 

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