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Complete 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 list:

  1. 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.
  2. If you removed it (again, not covered by this article) then reinstall the clutch basket.
  3. 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 firmly 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 more 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 preparing 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.
  4. If you removed it, or it fell out, reinstall the kickstart quadrant.
  5. 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.
  6. 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.
  7. 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 a 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 whichever 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.
  8. 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.
  9. Place right case half over the two studs, lining up with the fat locating stud near the oil filler plug and slowly wiggle/push/persuade 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 not 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 care not to damage the gasket or you have another spare if you need to separate the cases again).
  10. 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.
  11. 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 to go.

Next - Installing a Polini 130cc cylinder kit
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