Now that we have the engine/transmission assembly removed and ensconced on a clean and sturdy workbench, you need to give some thought to organization. You will be removing a lot of parts - both small and large - so find some appropriate receptacles and designate an area to temporarily store them away from the clutter so that they won't get lost. It's a good idea to take digital pictures and/or notes as you go along to refresh your memory on the order of reassembly when the time comes.
Don't rely solely on this tutorial for direction. I haven't documented every single step (that would have required maybe twice as many photos). I relied on the Malossi instructions that came with the kit, along with the Vespa factory service manual and a Hayes manual for further reference. If you use those three documents, along with this tutorial, you should be well-covered.
Fastener torque specs are available in all three sources.
First, I removed the air box and duct:
Then the inner fender:
Remove the carb and intake manifold (by simply removing the two bolts holding the manifold to the head) and start disassembling all the plastic shrouding:
You need to remove the SAS system to get all the shrouding off. Be careful undoing the nuts that hold the SAS pipe to the head. They are right next to the exhaust port and get corroded and seized from the heat. I managed to break off one of the studs:
Thankfully, these are common 6 mm studs (unlike the rare 7 mm exhaust manifold studs), and a replacement was easy to find. I was able to salvage the special long nut and remove the broken stud with extractors. Next time, I'll definitely use lots of penetrating oil and give it time to work.
Next, remove the four bolts that hold the valve cover on and remove it:
Note that I had removed the transmission cover. I did this because I was working on the upgear kit installation at the same time. If you are just installing the cylinder kit, there is no need to remove the transmission cover.
Next, loosen the central bolt on the timing chain tensioner:
Then, remove the bolt holding the bell encasing the camshaft automatic decompressor assembly:
...and remove the bell:
Then carefully remove the bobweight return spring:
Remove the M5 Allen screw holding the static weight and remove the weight:
Slide out the bobweight, being careful not to lose the little plastic yellow ring on the back:
Then remove the timing chain tensioner assembly altogether by removing the two cap screws holding it onto the cylinder casting:
With the chain now slack, you can remove the camshaft sprocket and spacer washer. Note that I ran a wire tie through the loop of the chain so that I can keep some tension on it while removing the head and cylinder. You definitely don't want the chain to come off the bottom sprocket during this operation or you'll be doing more major disassembly!;
Unscrew the four head nuts and the two long bolts on the timing chain side of the head and carefully slide it off, keeping a little tension on the timing chain as you do so:
Still keeping some tension on the chain, slide the cylinder off the piston and the long studs. You may need to tap the cylinder lightly with a rubber mallet to break it loose from its base gasket:
After blocking the opening of the crankcase with a clean rag, remove the circlip holding the wrist pin in the piston and slide the wrist pin out to remove the piston (the black object above the wrist pin is one of the belt tensioner shoes):
Malossi recommends a valve leakage test and replacement of the valve springs if the engine has a lot of miles. Mine had only 3700 miles, so I didn't worry about that. If your valves leak, they will need to be lapped, and the guides possibly replaced. Clean and decarbonize the head with a soft scraper and carefully remove all traces of the original base gasket from the crankcase.
Malossi recommends lapping the mating surface of the head to make sure it is perfectly flat. This is done by moistening a sheet of 1000-grit wet-or-dry sandpaper and laying it on a known perfectly flat surface (I used a machinist's granite surface plate, but you could probably use a smooth granite tile, a piece of float glass, or the machined top of a good table saw). Lap the head on the sandpaper until the mating surface is uniformly white, then wash off any residue:
Test-fit the new base gasket and cylinder, minding the chain all the while to make sure it goes together smoothly and that there are no casting flashings that need to be removed:
After carefully assembling the rings on the new piston in accordance with the instructions that come with the kit (be very careful, piston rings are very brittle and will break easily if flexed too far!), place a new circlip in its groove on one end of the wristpin hole, making sure it is well seated in the groove and the open gap positioned opposite the insertion recess:
Then, making sure the piston is positioned so that the arrow on it's crown is pointed toward the exhaust port, slip the piston over the end of the connecting rod and insert the new, prelubricated wrist pin. The next step probably requires more manual dexterity than anything else in the installation: insert the second new circlip. This will be vastly more difficult than inserting the first one, as the end of the wristpin is somewhat in the way. It is wise to remove clutter around your workspace and position some towels so that - if you lose your grip on the circlip - it won't go careening off into parts unknown. You can't re-use an old one, and there are no extras provided - so be forewarned! Again, make sure the clip is well-seated in the groove and the gap in the clip is positioned opposite the insertion recess:
Check to make sure the gaps in the piston rings are positioned as specified in the instructions, apply motor oil to the piston and rings and the cylinder bore, and then carefully slide the cylinder down over the piston, compressing each ring in turn until the cylinder can be pushed down to the base gasket. Then install the head gasket:
Reinstall the chain tensioner shoe, and -- minding the chain all the while -- slide the head on:
After properly torquing the four head nuts and the two long bolts to spec, re-assemble the camshaft sprocket and auto-decompression assembly. Position the timing chain on the sprocket making sure the "2V" mark on the sprocket is aligned with the reference notch on the adjacent casting when the crankshaft is in the "top dead center" position as indicated by aligning the reference marks on the flywheel (see service manual). This step is critical, as the valve timing will be off if this is not done correctly. Refit the chain tensioner assembly and tighten the center bolt, then re-check that the valve timing marks are still aligned.
The next step is to adjust the valve clearances to spec (detailed instructions available in the Wiki):
Then replace the valve cover, making sure that the gasket and its groove are cleaned and that the gasket is properly positioned. If there is any damage to the gasket, replace it. Torque the bolts to spec:
Apply anti-seize compound to the threads of a new spark plug, and insert it and torque to spec:
Before re-assembling the plastic cooling shrouds, take time to clean the foam filter in the SAS system, located at the top of the fan cover (it just pulls out):
Reassemble the plastic shroud (may require an extra beer and some cursing), reattach the carb and intake manifold, the inner fender, the air filter, and any other fiddly bits that were removed, and you're there!:
Don't forget to refill the crankcase with oil!
In the next part, Part 4, we'll tackle the installation of a Polini upgear kit.
⚠️ Last edited by Silver Streak on UTC; edited 2 times