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FITTING PISTONS A N D CYLINDER BARRELS

Pistons to be free of carbon on their crowns and ail piston ring grooves to be clean.
Piston rings to be clean and on pistons.

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Fit a piston to its connecting rod by:

Smear gudgeon pin with clean engine oil.

Place piston over connecting rod so that the slotted side faces to the front of the machine,
introduce  gudgeon  pin  to  piston  and  pass  through  connecting  rod,  press  right  home
against the circlip still in situ.  Then again, using pliers 011188, contract the other circlip,
introduce  same  into  its  groove  in  the  piston,  using  a  rotary  movement.  Make  quite
certain  that  the  circlip  lies  snugly  in  its  groove  because  failure  to  do  so  will  inevitably
lead  to serious damage.
(See  "NOTE"  above).
Before fitting the cylinders,  make sure they are clean  and  examine the  base washers and
renew same  if  not  perfect.
To fit a new cylinder  base washer:  first clean off the old  washer and  all  traces of jointing
compound.  Then smear one side of the new washer with jointing  compound  and,  when
that  is  nearly  dry  ("tacky")  apply  to  the  cylinder.
Place  rings on  piston,  scraper first,  then  the two  compression  rings.  On  all  models the
top  compression  ring  is  chromium  plated.  These  chrome  plated  rings  have  a  slightly
tapered  exterior and  when  new  are  clearly  marked  with  the  word  TOP on  one  side  to
indicate assembly position.  After use this word  tends to  become indiscernible,  but over
a  large  mileage  the  assembly  position  can  be  determined  by  brightness  of  the  edge
contacting  cylinder  wall.  This  bright  edge  is  the  lower  one.  When  as  the  result  of
wear,  contact  with  the  cylinder  wall  appears  uniform  over  the  whole  width  of the  ring,
it  is  immaterial  which  way  round  it  is  refitted.  The  650  c.c.  two-piece  ring  is  marked
TOP.
Space the  piston  rings  so  that  the  gaps  are  120°  to  each  other,  smear  piston  and  rings
and  bore of barrel with  clean engine oil and, supporting the piston with one hand, gently
pass over the barrel, compressing each piston ring with the fingers, as it enters the barrel.
Press  the  cylinder  barrel  right  down  into  the  throat  of the  crankcase.
Fit the second  piston,  gudgeon  pin,  rings and  barrel  in a like  manner.
Revolve the  engine till  the  pistons  are  at the top  of their strokes and  then,  with  a  clean
rag,  wipe off all  surplus  oil.  All  is  now  ready to  re-fit the  cylinder  heads.

TO RE-FIT T H E CYLINDER HEADS

Clean the valve stems and the  bores of the valve guides  with  rag  moistened  with  petrol,
make  sure  all  other  parts  are  clean,  then  smear  each  valve  stem  with  clean  engine  oil
and  proceed to re-fit the valve stems by reversing the procedure taken to dismantle them.
Insert  the four  valve  push  rods  into their original  positions  and,  after  making  sure that
the  cylinder  head  gaskets  are  undamaged  and  in  position,  proceed  to  fit  the  two heads
and  leave the  two  sets  of four  cylinder  head  retaining  nuts  finger tight.
Now  re-fit  the  inlet  manifold,  making  sure  the  two  paper  gaskets  are  undamaged,  and
leave  the  four  retaining  nuts  only  just  tight  enough  to  ensure  correct  alignment.
Next, fully tighten down the four  retaining  nuts on  each  head, treating each,  diagonally,
bit  by  bit,  till  all  are fully  down.
Then,  fully tighten  the  inlet  manifold  retaining  nuts  and  re-fit the  carburetter.
Next,  carefully  check  each  rocker  clearance,  as  previously  described,  and  re-set  if
necessary.  (The correct rocker clearance with cold engine is ·008" for inlet and exhaust.)
The  gaskets  under  each  rocker  cover should  be  inspected  and,  if  not  sound  should  be
replaced  after which the rocker covers can  be refitted.
Next  re-fit  the  cylinder  head  steady  plate  and  securely  tighten  the  three  fixing  bolts.
NOTE—Before  re-fitting  carburetter  make  sure  the  rubber  ring  in  manifold  joint  face

is in position and undamaged.

Oversize or undersize parts

Cylinder re-bore:

·020 in. and ·040 in. oversize

Pistons and rings:

·020 in. and ·040 in. oversize

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The following are the only "oversize" variations provided for the Vertical Twin machines.

Big-end and crankshaft centre main bearings:

Undersize

·010

·020