Series ‘A’ Valves

bmetcalf

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That is the design of AJS/Matchless 7R/G50:


AJS%2B7R%2C%2Bt-side%2Bsectioned%2Bengine%2Bdwg%2CMCing.1.jpg
 

Bill Thomas

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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
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

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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

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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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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

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Just trying to think what Harold Pass did, His Morgan three wheeler had an "A" Twin engine with strange valve
fitting. Cheers Bill.
 

kettlrj

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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

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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

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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

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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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