the big end assembly. To remedy—providing the roller path on the crank
pin and also the big end eye is not broken—a new set of rollers will take
up the slight movement.
A similar rattle that is not affected by engine load, on engines with a
number before 6850 is due to the stator in the crankcase breather being
loose, this being secured by the steel tube located between the rear of the
crankcase and the gear box. If the tube is broken the stator will move as
the piston travels up and down, causing the rattle. The stator part number
is 04220. On later engines the stator tube was discarded, the stator being
now located by a bolt which will be found below the drive side bearing
on the crankcase.
A rattle in the timing gear is due to wear on the cam followers, due to
excessive rpm causing valve float, or weak valve springs which would
have the same effect.
Excessive oil consumption. When the engine smokes unduly, and if the
cylinder has been rebored with a non standard piston in use, this is usually
due to an inefficient oil scraper ring in use. The Wellworthy DUAFLEX
ring—which is the best oil scraper ring—will cure this fault. In the event
of this type of ring being already in use it is possible that there is some
restriction in the crankcase oil filter causing oil to accumulate in the
crankcase which the oil control ring cannot cope with. To overcome this
possibility a longer crankcase oil filter was introduced and first used on
the 350 lightweight engines, useable for the 250 engine.
Oil can also accumulate in the crankcase if the cap for the filter 042064
is out of position blocking the oil return passage in the compartment for
the filter. If there is no improvement after dealing with the points given
then a rebore is necessary.
Crankcase bearings. Engines made in 1959 used two ball bearings in the
drive side crankcase, which had short life. This was overcome by using
a roller bearing in the drive side crankcase—on the outside—next to the
flywheel, where the maximum load occurs. See para Engine service for
fitting instructions.
Heavyweight Models
1947 MODELS
(1) Improved type oil-pump plunger (two start type) with new timing
side axle (identified by 2S stamped on plunger).
(2) Oil feed passage in timing side half crankcase increased to T"
diameter to prevent cavitation, with corresponding increase in
diameter of the oil pipe (
a" diameter).
(3) A two piece oil pump guide pin x" in diameter to prevent wear on
the pin due to the increased plunger speed.
(4) Shorter connecting rod for centres.
(5) The use of a long plain bush for the timing side bearings; the small
roller bearing is now obsolete. Engines fitted with the old type
bearing can use a modified bush with two external diameters. The
steel sleeve is retained to locate the new bush on the large external
diameter.
1948 MODELS
(1) Annular groove in pump plunger increased from
x" to ¼" diameter
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