T H E O L D G R E E N B E E M E R
RIDING A 1974 BMW R90/6 FLAT TWIN
ROCKER ARM END PLAY / FLOAT
Fresh from the Lab: A way to pre - set rocker arm end float
Excessive play between the rocker arms and their mounting blocks can be a source
of '' head " noise that amplifies the normal valve ticking into a loud staccato
Not what I like and not good for a long healthy engine life either.
Series /6 and earlier engines are notorious for this, there is no way of pre - setting
the amount of free play ... until now that is. This is where the custom made
excenters come into play, instead of ... the bronze mallet hammer.
The excenters are snug fit around the head stubs
As well as in the axle mounting blocks but still can be rotated
The mounting blocks are a very loose fit over the head stubs and can skate around
on top of them, not good. The excenter fits in the void in between the two and
by rotating it in the correct position clearance can now be pre - set
With the help of a wire hook tool the amount of clearance can be set
before the head bolts are torqued down
At one side the excenter is adjusted so that the rocker arm hits the valve stem at the
correct place, ( important : this is done with the blocks that are in the top side of
the engine ! ) then the other excenter can be adjusted for end play.
As you can see here: Adjusted for about 1/10 mm or a bit less
Note: The head bolts in the photograph are just for show
Installed in the head they serve another purpose as well: Keeping the blocks
from sliding off position caused by temperature variations. Note the block
is upturned, this is done to start wearing in on a new surface. The R90
has no additional bearings between the rockers arms and its keeper
blocks. In practice the amount of wear is nothing to worry about.
What you seen here is the result of approx 100k of service.
Continue to Carburettor Cold Starter
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