Recommended Rebore Oversizes; Tappets; Tappet Blocks; Pistons - Triumph SPEED TWIN 1945 Workshop Instruction Manual

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RECOMMENDED REBORE OVERSIZES ARE AS FOLLOWS:-
Cast lron Block +.010"/+.020"/+.040" 500
C.C.
Cast Iron Block +.010"/+.020" 650
C.C.
Alloy Block +.Olo"]+.020" 500
C.C.
It
w ~ l i be noted that the alloy block can only be re-bored t o a maximum o f
+
.020°.
this
i s
due t o the fact that cylinder liners are fitted. Further re-boring would t h i n
down t h e liner beyond safety limits. it is pos's~ble
t a
change t h e liners, b u t w o r k
such as this should only be entrusted t o a competent engineering concern, w h o
w i l l have the necessary eqqipment.
Tappets.
The base of the tappets have a "Stellite" t i p fitted ; this material has
grear resistance t o wear and under general running conditions t h e tappets w i l l n o t
require changing until a considerable mileage has been covered. The centre o f t h e
t i p may show signs of indentation which
i s
caused by the peak of the cam. This does
n o t however indicate wear and the tappet can be re-insraiied.
T a p p e t Blocks.
It
i s
not necessary t o remove t h e tappet blocks f r o m t h e cylinder
base f o r inspection
;
the amount of wear can be estimated by rocking r h e tapper
head. The tappet stem should be a sliding fit i n the tappet block bores and t h e
tappet base must fig snugly i n the block base. Slackness at these points w i l i cailse
excessive mechanical clatter. T o remove the tappet blocks f r o m t h e cylinder base
flange, place the cylinder block downwards on the bench, remove t h e locking screw
and d r i f t t h e tappet block o u t of the cylinder flange. W h e n fitting t h e new tappet
block, grease the outer surface and i f possible support t h e cylinder flange (See
Fig. 14). D o not forget t o line up the locking screw hole I n t h e tappet block t o
that i n t h e flange. Replace the locking screw.
Pistons. If the pistons are t o be further employed, the rings and gudgeon pins
when removed from each piston should be kept separate t o ensure correct replace-
ment. Carefully clean away the carbon deposit from the piston crown, taking
particular care n o t t o scratch the metal surface. The light deposit o f b u r n t oil i n
the piston s k i r t should be removed by rubbing w i t h a rag which has been dipped
i n pettol. Never i n any circumstances use an emery cloth.
T o clean t h e ring
grooves, it is advantageous t o use an old broken ring by inserting t h e broken end
i n t o the groove and working it around t h e circumference. Clean o u t t h e o i i drain
holes i n t h e scraper ring groove and thoroughly wash the piston. Or, t h e irkside
surface of t h e piston rings w i l i be found
a
light deposit of carbon which must be
removed i f the rings are t o be re-fitted.
N o w r o l l each ring around i t s respective groove t o ensure that
it
does n o t stand
proud of the piston after being fitted correctly and compressed. Before fitting n e w
rings, the gap must be checked in the lowest part o f the cylinder bore. The rirry
must lie square t o the bore for checking purposes and t o ensure this, place t h e
bottom1 of the piston skirt onto the ring and ease
it
about
f"
(13 mm.) down t h e
bore. Check the gap by feeler gauge.
Min.
Max.
Compression Ring Gap
...
0.010" (0.25 mm.) 0.014" (0.35 mm.)
Scraper Ring Gap (500 c.c.)
...
0.007" (0.18 rnm.)
0.011" (0.28 mm.)
,,
..
,,
(650 c.c.)
...
0.010" (0.25 rnm.) 0.014" (0.35 mm.)