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Page VI
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SCHEDULE OF CLEARANCES & TOLERANCES (V:
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All threads ~ed 00 the L4 Eogine except 00 prGprietary equipment
and the crankshaft are Unified Series, aod Americao Pipe Series. Tbe
crankshaft aod starting dog nut are threaded 1 inch Americao Natiooal
Fine of 14 T.P.I.
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The new threads are not interchangeable with B.S.F. and althougb
B.S. W. have the same number of threads per inch as the Unified Coarse
Series, intercbanging is not recommended, doe to a difference in thread form.
The data regarding clearnnces and tolerances are given as a guide
for personnel engaged upon major overhauls.
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Tbe figures in the column .. Permissible Dimensions ,t are the
drawing sizes to which tbe parts are made. These dimensions are
given in limit farm and represent tbe minimum and maximum sizes
to which parts may be accepted when new, as, ror example,
.4985
111,ntPn fnr " qh"ft ni"m~tpr
2.
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3.
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4.
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5.
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6.
-:499 '1 .-. - ~ The difference between the minimum and maximum dimensions
quoted in para. 2 is known as thc manufacturing tolerance. This
tolerancc is necessary as an aid to manufacture and its numerical
valuc is an expression of the accuracy of the design; it mayalso be
considered as a numerical expression of the desired quality of work-
manship. For the example referred to in para 2 thc tolerance is
0.0005.
If when carrying out a major overhaul it is found that a bush and
corresponding shaft have worn and that the majority of wear has
taken place in the bush it may be necessary to renew the bush only.
Similarly if the majority of wear has taken place on the shaft it
might only be necessary to rencw thc shaft.
During the overhaul of wom components personal initiative must
be exercised at all times. It is obviously uneconomical to return
wom parts to service with an expectation of lire which may involve
labour costs agaiÎ1 at an carly date.
Further information can be obtained on request [rom the Service
Division, Perkins Engines Ltd., Peterborough, England.
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To ensure rou obtain the best results from your engine
and to safeguard your own guarantee, fit only genuine
Perkins Parts. These are readily obtainable throughout
the wor Id.
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