Vespa 150cc Top End Install - How-To w/ pics

This project was done over two days. Normally it would take about 25-30 minutes but I was waiting on the head to arrive. I tried to make the photos as clear as possible and will do the same with the instructions. 

So here we go!

Tools:

11mm socket and ratchet

small needle nose pliers

mallet and wood block (optional)

Time:

20 minutes

The first pic shows everything but the head and head gasket. The motor is on the stand and we're ready to begin.

1. We begin by putting one of the wrist pin cir-clips into the piston. Do this in a well lit area and don't force it. The process should be pretty easy but if the pliers slip, the clip will spring out and could be lost. I usually cover my work with my other hand to prevent this problem.

2. Next, apply the piston rings. There are really 2 ways to do this. First notice the small notches in the piston ring groves of the piston. You want to place the gap of the rings identically so you can later compress them. Option 1 is to use snap ring pliers but they always slip on me. Instead (option 2), I just start at one end and carefully work my way around. Be careful not to flex the rings too much since they can break pretty easily with too much force. 

How do I know if my rings are upside down?

If you look closely at your rings, you'll notice they  have tapered ends. The wide end should be up.

3. Okay, now we flip the cylinder upside down and slide the piston in from the bottom. You can compress the rings by hand as you slide the piston in. Be sure to note the piston side chambers must match the cylinder chambers. I am using 2-port cases and a 2-port cylinder kit. The 2 side ports match the cylinder and the final port points down at the exhaust outlet. Be sure not to slide the piston all the way inside the cylinder yet. We need the wrist pin hole to be sticking out a bit. See the pic.

4. We're just about at the half way point now. Guide the base gasket down the cylinder studs being sure to match up the case ports. Slide the base gasket down onto the Slide the assembly we've created down along the cylinder studs. Needless to say, exhaust port down. Be sure your wrist pin bearings are in the small end of the crank arm and slip the small end of the crank arm inside the back end of the piston. Be sure not to push on any parts too much. This last step should be effortless. If there are any hang ups or difficulties, stop. Go back. Check to make sure everything looks correct.

5. Now line up the hole of the crank arm with the wrist pin hole in the piston and ease the wrist pin all the way in. The pin usually doesn't slide straight in. Normally, I twist the pin in my fingers as I slide it in and it finds it's place pretty quickly. Once the pin is in, insert the other wrist pin clip. Hell yeah. Almost done.

6. Next slide the cylinder down to the base of the block. This should be relatively easy but sometimes with brand new parts, it takes a light tap or a mallet. I recommend placing a piece of wood block between the cylinder top and the mallet for safety safe.

7. Still Cool? Okay, now drop the head gasket (a head gasket is actually optional) on and then the cylinder head. Make sure the hole in the head for the spark plug is pointed upward.

8. Now hand tighten all your cylinder stud bolts. The long stud bolt should be at the top right (see pics). The end of it has a small bolt and lock asher for bolting down your cylinder shroud (not included in this how-to).

Using an 11mm socket, Tighten in a cris-cross pattern starting from top left. Be sure not to try to tighten the thing down on the first round. This can mess up your base gasket seal, head gasket seal, strip your bolts, and cost you money. Just take it easy as you go around. Eventually, give everything a nice snug final turn making sure the parts are seated adequately.

9. Finally, step back and bask in the glow of your work.