750 SF Crankshaft

S

Stu

New member
Location
South Wales, UK
I am trying to fit a reconditioned crank but I think that I may have a problem. The half ring (a snug fit in the crankcase) that locates the outer bearing on the starter side is narrower than the groove in the bearing, which would potentially allow a small sideways movement of the crank. Everything fits nicely when its over to the drive side but pushed the other way the oil thrower on the drive side is very close to the web for the centre bearing. Also the outer race of the drive side roller bearing is about 1mm away from the half ring on that side. Is this normal or should the outer bearings be shimmed?
 
Although I have not rebuilt a 750 in many years, I seem to remember on the very early 750's there were differences on the bearing half ring. It seems in mid 1968 the ring got wider and bearing was different.

Bruce
 
1200ts said:
Although I have not rebuilt a 750 in many years, I seem to remember on the very early 750's there were differences on the bearing half ring. It seems in mid 1968 the ring got wider and bearing was different.

Bruce
Click to expand...

From memory, early ones had the outer bearing cage located by a half ring external to the bearing cage, later ones by a half ring locating with a groove in the bearing outer (or vice versa). In no way is there 1 mm play.
Paul
 
There is always a small amount of movement possible at the half-rings, the RH ball bearing locates the crank in the cases.  The LH bearing actually needs a bit of space to allow for heat expansion.

Early twin cranks had ball bearings at both ends, both fixed by half-rings.  Apparently they did not stand the load on the drive side or were overloaded by crank expansion and were replaced by rollers quite quickly.  The outer roller race is located by a wide half-ring next to the race.  1mm clearance does sound excessive, but if nothing rubs, it should be good to go.

piet
 
sfcpiet said:
There is always a small amount of movement possible at the half-rings, the RH ball bearing locates the crank in the cases.  The LH bearing actually needs a bit of space to allow for heat expansion.

Early twin cranks had ball bearings at both ends, both fixed by half-rings.  Apparently they did not stand the load on the drive side or were overloaded by crank expansion and were replaced by rollers quite quickly.  The outer roller race is located by a wide half-ring next to the race.  1mm clearance does sound excessive, but if nothing rubs, it should be good to go.

piet
Click to expand...

Change to LH roller bearing was sometime in 71 if I remember rightly. Primary drive load too much for balls, a common mistake apparently.
You'll find early engines converted to roller with the crankcase drilled and tapped with a screw and small plate to abut the bearing outer cage.

Anybody opening an early engine that has a ball LH main bearing should replace it with a roller as a matter of course.

Paul
 
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