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Yamaha oil pump
rebuild
This presentation deals with the rebuild of any of=
the
one or two cylinder oil pumps that were fitted to all Yamaha bikes from 19=
63
up to the early 1970’s.
There was virtually no difference in any of the pumps over the year=
s.
The main difference was variations of the pump body and the positioning of=
the
outlets. All flow rates are controlled from within the pump and are
non-adjustable. The only pump adjustments that are possible is the pump pulley setting (done =
by
adjusting the pump cable) and also the pump stroke at idle (performed by
adjusting the shims under the pump pulley). The pump used in this rebuild =
is
from a 1965 YDS3C Bigbear
1.First job is to remove the oil pump c=
over
held in place by the 3 No 3 Phillips screws on the clutch cover.
=
2.Next, get a suitable container undern=
eath
where the pump is as oil always spills out of the pump when removed from the casing. Disconnect and plug the oil suppl=
y line
from the tank with
a 6mm bolt or screw pushed into the pipe.
3.Remove the 8mm headed bolt that holds=
the oil
line to the left cylinder. Note
that there is a spring
and a small ball bearing under each of the 2 oil line banjo bolts. I sometime find it easier disconnecting the lines from t=
he
bottom of the cylinder barrels as the lines get very brittle with age and are easy to brea=
k, it
also makes it much easier getting the right hand oil pipe off.
4.Next, remove the 2 screws that attach=
the
pump to the casing, they are No2 Phillips headed ones.
5.Gently prise the pump from the casing=
and
slide it out far enough to enable you to remove the back oil line retaining banjo bolt, <=
/span>remember the spring and ball beari=
ng. I screw the banjos bolts back in with the springs so not=
too
lose the ball bearing and springs.
6.Last job is to remove the pump cable =
and
we’re ready to strip the pump.
The pump I am stripping came off a bike that had o=
nly
done 3,500 miles and was leaking oil from the seal under the white plastic
pulley wheel indicating that the seal had failed. Below are 2 pictures of =
the
removed pump.
![](3D"slide0004_image002.jpg")
![](3D"slide0005_image004.jpg")
First job is to remove the 2 banjo bolts, the 2 sp=
rings
and the 2 ball bearings. Also remove the pump bleed screw located at the t=
op
of the pump in the picture. The balls can be reluctant to come out, so a s=
harp
tap against something can usually loosen them. I also turn the white pump
wheel as though you were priming the oil lines, this puts pressure on the =
ball
and releases it, you will see air bubbles being forced past the sticky ball
valve. On removing this pump, there was found to be some black sludge in t=
he
bottom of the it and also one of the balls of the non return valves was ve=
ry
reluctant to come out of the left hand line side. The engine had shown sig=
ns
of piston seizure in the past on the left side so this could be a possible
cause.
![](3D"slide0006_image006.jpg")
Next step is to remove the 9mm nut that holds the =
pulley
shaft on. Note the wave washer underneath the nut. Remove the adjusting pl=
ate
(as it is called in the manual) and carefully remove the shims sitting on =
top
of the pulley. Keep these safely together. Gently pull the knock pin holdi=
ng
the pump pulley out with pliers, try not to damage it too much when removi=
ng
it. The pump pulley will now pull off the top of the shaft followed by the
spring.
![](3D"slide0007_image008.jpg")