Vespa smallframe engine strip down and rebuild.
11. Reassembling the engine.
Well, you've reached this page, so you might be forgiven for thinking
that all the hard work is done and it's all downhill from here.
Not so. Reaasembling the engine is one of the trickier jobs. First
you have to make sure you have remembered everything, and then you
need to be concentrating on several things at once.
Before you reassemble, if you are installing a new cylinder kit
(see next page) you need to check the
fit of the cylinder on the cases, filing and adjusting if necessary,
and if you are going to be porting the cases to match the kit then
do this before you reassemble the engine. Otherwise you are ready
to assemble the cases again.
Reassembling case halves basically comes down to following an ordered
- Install the clutch side and flywheel side oil seals if you haven't
already done so, and all main bearings (though removing them was
not covered in this article), and install new kickstart rubber
buffers. The old ones are almost certain to be wrecked. They are
cheap as chips.
- If you removed it (again, not covered by this article) then
reinstall the clutch basket.
- Reinstall the rear axle/gear selector shaft.
To do this you will need to put your case half on the stove
with the rear axle
bearing ring on the gas to heat it. You can also heat it with
a blowtorch. Once this bearing is hot you should be able to
slide the rear axle right in in one movement. If it gets stuck
halfway you need to tap it back out, heat the bearing some
and try again. Trying to force the rear axle in can result in
the bearing ring being knocked out. You could freeze the rear
axle as well, but it should not be necessary. When you are
to slide the axle in pull the gear selector "wishbone" towards
you and slot the rotating rectangular pads into the groove around
the gear selector so that the gear selector will now be
activated by the lever.
- If you removed it, or it fell out, reinstall the kickstart quadrant.
- Install the kickstart idler gear, making sure you install all
the springs, cupped washer etc in the right place and the right
way. Rotate the kickstart quadrant to allow the gear to go on.
- Install the gears and shims, making sure everything gear is
on the correct way round. If all is correct the spacing between
the gears should be about equal and there should be no play. Once
you're satisfied the gears are on correctly, install the shim
and the large circlip to keep them on.
- Now you can install the crank. There are two
types of flywheel side crank bearing - one piece, found on
50cc or PK models and
two piece, found on the others. If you have the two piece bearing
you should put the crank in the left case half. If you have
one piece then first install the "Christmas tree" gear
shaft into the right case half, then install the crank into the
right case half. You will undoubtedly need to heat the cases
way you do it, so pop the case on the stove or use a blowtorch
as you did with the rear axle. Freezing the crank will help.
- At this point you should be ready to mate the two halves. Check
everything is in place, and when you are satisfied get a new case
gasket and apply it to the left case half with some thinly spead
gasket sealer or silicone bathroom sealant. once it's on, smear
another thin coating on the other side of the gasket and prepare
to mate the two halves.
- Place right case half over the two studs, lining
up with the fat locating stud near the oil filler plug and
the halves together. The "Christmas tree" shaft goes
through the kick-start gear through to the clutch basket. It's
important to do this all carefully so as not to dislodge something
or break anything. The gears will not mesh at first so you need
rotate the axle, and shimmy the cases together/apart/together
until the halves meet smoothly and you can still rotate the engine.
Gently moving the kickstart will help here. While not exactly
comparable to slipping a chainsaw through a trifle it should
take a lot of force to put the cases together so if it really
difficult then something is not installed correctly. Separate
the cases again and check everything and then try again take
not to damage the gasket or you have another spare if you need
to separate the cases again).
- When you have got the case halves together then put the correct
washers and nuts on the two engine studs and tighten them down
(not too tight - just snug). Now before continuing you should
check that everything still rotates smoothly and nothing is jammed.
You don't want to discover a problem later - Fix it now and it
costs you time, but procrastinate and you'll be buying a new engine.
- Install all the case bolts, washers and nuts. Evenly tourque
them down. These nuts can strip threads and bolts can shear, so
don't go mad. About 45lb/ft is correct. (Or as tight as you can
do it with your socket set with firm arm pressure, not a bloody
great long breaker bar!)
That's the engine cases together, and this job is beginning to
look like the end is in sight. Just the cylinder, clutch and flywheel