Lorenzo's XS650 has proven to be in rather better condition than I'd expected after being stored in a damp cellar for over five years. A full strip of the engine revealed no major problems, only the front camchain slipper blade being urgently in need of replacement. I've had the head and barrels bead blasted and we've opted to replace the camchain, so armed with a gasket set and a full set of replacement oil seals I'm now ready to rebuild the engine.
||1. The roller bearings fitted to the main
and big ends are more or less bulletproof unless a major lubrication failure
has occurred. The crank has shown no signs of distress, so I'm happy about
re-fitting it. The starter drive gear, indicated, shows some signs of
wear but this is not excessive.
||2. Before assembling the crankcases I start
by re-fitting the starter crossover shaft and it's drive gears. This can
be really difficult to engage later, as I discovered during the engine
||3. The gear selectors also need to be assembled
into the top crankcase half at this stage. I've been careful to keep the
three selector forks in order, and can simply slip them over the selector
drum as I slide it into the crankcase. Each selector fork then needs its
respective pin sliding into place until it engages with the track on the
selector drum, then I slide a cotter pin into place and bend the ears
over to secure the pin.
||4. This cross shaft also serves to locate
the three selector forks in the correct position. There's a fair amount
of movement in the selector forks with everything correctly engaged which
undoubtedly helps gear selection, but is also probably responsible for
the traditional Yamaha "clunky" gearbox.
||5. Now I can position the crankshaft and
the two gearbox shafts into position in the upper crankcase half. I've
placed new oil seals on each end of the crank and on the gearbox output
shaft at this stage, and made sure the gearbox bearings are engaged with
their respective locating rings in the crankcase. I'm fitting a new camchain
too, so I've hooked it around the crankshaft before proceeding.
||6. After applying a thin smear of Blue Hylomar
to the jointing faces I can now fit the crankcase halves together and
refit and tighten the bolts. The workshop manual gives a tightening sequence,
but if in doubt I always tighten the bolts in a diagonal pattern working
from the centre of the engine outwards. Make sure the shafts rotate easily
in their bearings before proceeding. The starter motor fits underneath
the XS650 engine, so I re-fit it now to save problems later. The starter
reduction gears can then be fitted as an assembly to the left side of
||7. Turning the engine right way up, I can
now lower the barrels into place after greasing and fitting a new base
gasket and "O" rings. Many people like to use ring compressors for this
job, but I prefer to gently ease each ring into the freshly oiled bore
with the aid of a small screwdriver. Once all the rings are engaged the
barrels should tap gently home with a rubber mallet.
||8. With the barrels seated on the crankcase
mouth I can fit the new front slipper blade into position and bolt it
up with the two M6 bolts. The cylinder head then simply slides into
place over the studs, having first made sure all dowels are in place,
and I'm ready to re-fit the camshaft.
||9. As with all engines, the valve timing
needs to be spot on and it's worth taking time to check and double check
the timing before progressing. I've started by temporarily re-fitting
the generator stator which allows me to accurately line up the "T" mark,
ensuring the engine is at TDC.
||10. The camshaft now drops into place in
the head, and I've rotated it to line up this punchmark with the cylinder
head flange. This will index the timing correctly. The new camchain
is wrapped around the sprocket and temporarily retained with a loop
of electrical wire to stop it dropping into the engine while I double
check the timing marks.
||11. Riveting up the soft link into the
new camchain is a delicate job as it's easy to drop the link or its
end plate down into the engine. It's possible to buy a special tool
for riveting up the link but I've always got satisfactory results using
a nut splitter like this.
||12. With the camchain tensioner re-fitted
to the rear of the cylinder block I can now tension up the chain. On
this design the threaded sleeve winds down around the plunger until
the plunger end is flush with the housing. This correctly pre-loads
the tensioner spring. The new camchain was quite a tight fit, so I've
set the tensioner up with almost zero pre-load for the time being. It
will need checking once the engine has run.
||13. Next, the rocker cover. I've already
re-fitted the rocker arms, but these four sleeves need to be pressed
into place with new O rings before fitting the cover. The sleeves and
O rings will prevent oil leaking out past the head bolts. A thin smear
of Blue Hylomar will seal the rocker cover to the cylinder head.
||14. This is a convenient time to set the
valve clearances. These could close up slightly once the engine has
started up, so I'm setting them slightly wide. I'll be re-checking them
once the bike has run after the rebuild.
||15. All that's left to assemble on the
top end is the ignition components. With the points and auto-advance
housings re-fitted to the head with new gaskets and oil seals, I can
lightly grease the crossover shaft and slide it through the camshaft.
||16. The auto-advance unit fits onto the
right hand side of the crossover shaft. The easiest way to fit it is
to locate the baseplate first and clamp it up with its locknut. The
centre boss then slides into place before engaging the bobweights and
tightening the centre nut. Each bobweight is retained by a tiny circlip
which needs to be carefully clipped into place.
||17. On the other side of the head I can
now re-fit the points backplate. Before removing it I took the precaution
of scribing a reference mark on the housing face. Now I can simply line
up my reference marks and clamp up the screws. I'll be checking the
ignition timing with a strobe once the engine is running to make sure
its spot on.
||18. Now for the clutch and primary drive.
I've opted to start by sliding the starter bendix assembly onto its
shaft. The whole starter clutch mechanism is unusual on the XS650, the
starter motor drives a set of reduction gears on the left side just
beneath the gearbox sprocket. Drive is then transferred to this bendix
assembly via a crossover shaft. A rather convoluted system which suggests
that the electric starter was adapted to fit an engine originally designed
for a kickstarter only.
||19. Next I'm refitting the detent roller
to the end of the gear selector drum. This clicks the selectors into
their correct position when changing gear. Make sure the return spring
is in good condition and correctly engaged.
20. The gear selector shaft can now be
fitted. The shaft slides right though the crankcase, the selector
claw engaging with the pins on the end of the selector drum. I've
taken the precaution of fitting a new gear shaft oil seal into the
left side of the crankcase first.
||21. With the gear selectors in place the
clutch can be rebuilt onto the input shaft. A washer and spacer slides
onto the shaft first, followed by the clutch basket and inner drum.
I've used a new locktab on the clutch centre nut to make sure it can't
loosen off later. Before the clutch plates go back in I've done a quick
check for worn or buckled plates. Then with the clutch pressure plate
fitted the primary drive and oil pump drive gears can be re-fitted to
||22. The oil pump assembles into the inside
of the outer clutch casing. I'm taking the precaution of priming the
pump with lots of fresh engine oil to give the lubrication system a
hand when the engine is started for the first time.
||23. After refitting the oil pump drive
gear the tacho drive shaft slides downwards into the clutch casing to
engage with its worm drive. The tacho drive boss, with a new oil seal
fitted, slides over the shaft and into place in the casing, and is then
secured with its lock screw.
||24. After greasing and fitting
a new gasket the clutch case then goes back on the right hand side of
||25. Finally, before re-fitting the engine
in the frame, this rubber faced guide plate clamps in place around the
gearchange shaft. This not only protects the shaft itself, it also stops
the drive chain cutting into the alternator wiring. The rubber facing
on this guide plate is quite heavily worn but is still serviceable.
With the engine re-built we're now ready to fit the engine back in to the frame. However Lorenzo, the bikes owner, has been so pleased with the condition of his engine the he's now considering a full restoration to take the bike back to its former glory. The next step is to get the frame powder coated, then we'll be looking at some re-chroming and new paint as funds become available. I've a feeling this could turn into an extended project, so I'll keep you posted on developments as work proceeds. In the meantime the engine will be kept safe, dry and warm in Lorenzo's living room.
Thanks to Granby Motors of Ilkeston (tel 0115 944 1346) for their help with gaskets and spare parts for the re-build.