An Overhead-valve Extractor.
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T T IS a well-known fact that overhead I valves of the cage or box type are most difficult things totake out. To extract the cage when this is a tight fit, through carbonization or seizure, is well-nigh impossible without breaking or damaging something, unless a. special tool is used for the","operation.
An extremely useful and well-designed tool for this purpose is made by Mr. P. Edgerton, of 120, Queen's Roe& Aston, Birmingham. Alt-ho-ugh the Edgerton overhead-valve extractor has been designed primarily for Maudslay lorry engines,,the same type of tool, made to special dimensions, may be used for all engines with box-type valves.
The extractor consists of a cast-iron bottle-shaped body, the inside diameter of which is slightly greater than the outside diameter of the valve cage, allowing the latter to be drawn inside the former. Passing through a clearance hole in the top of the body is a drawbolt with a quick thread, at the end of which, inside the body, are three hooks of great strength. Before using this extractor, it is necessary to replace the standard valve spring caps by special ones with a coun B26 tersunk groove, machined on the underside, to enable the grappling hooks to obtain a good purchase for extracting the valve cage.
To extract a valve cage, the extractor is placed over the valve and the hooks engaged in the valve spring cap (the sides of the body are cut away to allow this to be done); a nut is then screwed down the drawbolt and pulled up against the top of thr, body. 'Two turns of the nut are usually sufficient to loosen the cage, which may then he drawn.out with ease.
In the case where a valve is broken, it is then much more difficult to extract the cage. To meet this emergency, a special collet is supplied which has two deep slots cut diametrically at rightangles to one another. This collet is screwed into the drawbolt, and the slotted end, which is tapered up to a shoulder about in. from the end, is forced down the valve guide until the shoulder is clear of the guide, when it expands. The drawbolt is then screwed. up and the shoulder of the collet pulls against the cage, extractimg it. The price is 35s. complete with a set of valve spring caps and collet.