More about improving your A10.
End feed oil conversion.
After discussing the proposed rebuild with other long distance bike riders and
considering we proposed to do about 10,000 miles a year two up, including at
least 2 continental trips per annum I decided that the only thing for this bike
was an oil end feed roller bearing conversion courtesy of SRM. The next weekend
saw us on a trip to Penarth Docks in South Wales (they have since moved to a
new 7000 Sq ft factory unit in Aberystwyth), armed with crank, crankcases, oil
pump, oil pump drive pinion and securing nut, intermediate timing pinion and
inner and outer timing covers. I was given a job number to quote when making
enquiries about progress on my engine. Each part was marked with the job number
so you receive your original parts back. The conversion has two major benefits.
Firstly the big ends get a regular supply of oil at a decent pressure and the
crank runs in a roller and ball bearing on the timing-side. With the standard
arrangement when the plain bearing and timing side bush wore it allowed the oil
pressure to drop and the drive side big end (farthest from oil pump) would
seize. This would often cause the conrod to break and punch a hole in the
crankcases. I know! This happened to me once, it also broke the crank. Very
expensive, worth balancing the cost against the price of the end feed
conversion. At SRM the oil pump is checked for its output delivery as this must
be good enough to give constant pressure to the big ends. A decent oil pump
will easily give over 100 lb when the engine is cold. Then the crankcases are
degreased and checked for cracks and other major flaws. The first step in the
bearing conversion is to bore out the timing side crankcase to a larger
diameter. This is cut very accurately using a vernier adjustment on the boring
tool. The bearing, a combined needle roller and ball unit with a split race to
facilitate assembly is positioned by leaving a shoulder in the cases. When
assembled the crankshaft is bolted tight |
to this bearing but only after the mainshaft
faces are ground to give 10 thou clearance. Because a ball race is included in
this bearing this locates the crank axially so it does not require shims, which
means less work to do when rebuilding. The bearing race is fitted after the
crankcase is heated to 1000C. Although the journal is bored to a 2 thou
interference to fit the bearing, it drops in cleanly. This fit is tighter than
the normal thou and a half to enable the bearing to remain tight even at the
very highest temperatures encountered in some exotic countries where SRM have
customers, so it should be OK here at home in Manchester, England when we have
our 2 or 3 hot days of summer! For my engine I specified the RHP roller bearing
for the driveside. This was more expensive but when compared to an SKF or NACHI
bearing it is easy to see that there is an extra roller or two and that these
rollers are also up to a third wider, spreading the load over a greater area.
The bearing is degreased then the drive side casing is heated and the bearing
dropped in. If the case is already worn, a phosphur bronze insert is fitted to
bring the housing back to standard size. Next the timing side case has it's
oilways modified. This involves drilling the oilways to connect the oil pump to
a hollow dowel fitted at the bottom of the timing covers from where new oilways
are drilled into the additional casting which is Lumiwelded into the outer
timing cover. From this casting, oil is then fed into the end of the crank
through a quill pushed into a new drilling in the end of the crank through to
the big end oil feed. At this point the non-return valve on the exit is also
modified. Originally this was designed to stop the bike wet sumping, but, to
enable the ball bearing to be re-seated, it was necessary to split the
crankcases. To replace it, this oilway is drilled out to 5/16" , the inner
part is then sealed off. The spring and ball are dropped in from the outside so
that the ball bears on the back of the oil pump making it easier to seat the
ball if wetsumping occurs. This would be a good mod to do on your engine next
time you have it apart and will save you buying an external non-return valve. |