FREE BOOKS

Author's List




PREV.   NEXT  
|<   31   32   33   34   35   36   37   38   39   40   41   42   >>  
centre, where the exhaust valve should close, and so on till the opening and closing of each valve has been checked. It will be noticed that the air, and sometimes the gas, valve opens before the exhaust closes. This overlap is necessary; and it will be found that the smaller the engine and the higher the speed the greater this overlap will be to obtain good results, although a good deal of individual judgment must be used in settling the exact amount of overlap, as the requisite amount may, to get the best results, vary in different engines of precisely the same dimensions and type. When dealing with engines which have no separate gas valve--the gas being admitted with the air, which is sometimes the case with very small engines--the above notes referring to the gas setting independently, will, of course, not hold good. It may be mentioned with regard to the lump on the opening side of the exhaust cam, that this if overdone is found to be detrimental on large engines, and even on small ones. If it is too large, it will cause both exhaust valve and seat to become burnt and pitted, due to the surface being exposed to the exceedingly high temperature of the expanding gases. If it is too large, it is equivalent to opening the exhaust valve too early, and the effect is the same, viz., a waste of power and damage to the valve and its seat. [Illustration: FIG. 43.] [Illustration: FIG. 44.--Brake Testing.] The method of grinding in the valves to their seats with emery powder and oil is so well known that no further description is needed here. We give, however, in fig. 43 a sketch showing a very expeditious way of dealing with very badly worn or burnt seats. The sketch explains itself. Such a tool is readily made; even the cutter could be turned and filed up to shape and then hardened at home. By lightly tapping in the taper cotter pin little by little, sufficient pressure is put on the cutter to make it an easy matter to completely re-face an old seat or form a new one. A T-wrench or "tommy" can be used to work the cutter spindle. The lower part of the latter must be the same diameter as the existing valve spindle; the bush acts as a guide; and as the bevel of the cutter should be the same as that of the valve, a very little grinding in with emery powder is required to finish the job off. In fig. 44 we give a diagram showing the method of testing for Brake H.P. of engine, as it is frequently interesting to make suc
PREV.   NEXT  
|<   31   32   33   34   35   36   37   38   39   40   41   42   >>  



Top keywords:

exhaust

 

cutter

 
engines
 

overlap

 

opening

 

spindle

 

amount

 
dealing
 

results

 

powder


method

 

showing

 

grinding

 
sketch
 
Illustration
 

engine

 

hardened

 
description
 

needed

 

turned


explains
 

expeditious

 
readily
 

required

 

finish

 

diameter

 

existing

 

frequently

 

interesting

 
diagram

testing

 

pressure

 

matter

 
sufficient
 

tapping

 
cotter
 
completely
 

wrench

 

lightly

 
exceedingly

requisite

 
settling
 
individual
 

judgment

 

precisely

 

admitted

 

separate

 
dimensions
 
obtain
 

checked