MOPED ARMY

Chris,

The problem you face is that the Italian version of this motor was designed with a 10 mm wrist pin (called a gudgeon pin by the British) and the export model shipped with a 12 mm wrist pin. When I installed kits on mine, I machined new connecting rod bearings out of high speed bearing bronze. Have a machinist make you a bearing (it is just as easy to make two, so have him make an extra) with an outside diameter of 14 mm and an inside diameter of 10 mm.

Let me know if you have trouble, I may have an extra laying around.

Chris S

I used a head gasket that came with the 70cc kit. The problem isn't really the pin/bearing...I could use the stock one, it is the piston...the holes are made for the smaller pin/bearing thing. I am not sure that a machine shop could really drill it out either, considering the knitch for the c clips.

The stock Grande, and the other vespa mopeds I've worked on don't use a head gasket. Adding one will lower the compression.

the Kinetic, which is a vespa copy does use a headgasket, but i attributree that to lower quality machining.

Jim

Crisis,

Chris may be getting a little frustrated by now, let me try. : )

The "thing" between the piston and the crankshaft, is the connecting rod. It has a big end bearing (around the crankshaft) and a little end bearing that the piston pin fits through. Yes, other than "thing", these are the correct names. In the car world, when you "spin a rod bearing" it is the big end you just totalled. When you "throw a rod" The big end has separated from the crankshaft and come out through the side of the block and/or the oil pan.

Ok, enough terminology. What Chris is saying is that your little end bearing is 2mm too large, apparently because it is an export model. The little end bearing is a bronze bushing, or tube, pressed into a hole in the small end of the connecting rod. Chris is sugesting that you replace this bushing with one that has the same ouside diameter, but an inside diameter that fits the piston pin.

If you don't understand this, I am going out in the yard and eat worms. : )

Ron

So....AHHHHHHH. There is a connecting rod bearing inside the hole where the piston pin goes? I didn't notice a bearing, just the hole that I put the piston pin through. So, I can get one made to fit my stock connecting rod, little end, that will be tight enough to work with the smaller piston pin. I got it now!...I think :). I guess that I should have looked at the connecting rod a little closer. As far as the head gasket goes...I am going to go take it off right now and see how it runs. The new base gasket, and decarbing the cylinder, might have been all that I needed in the first place. I don't want to be losing power...That's for sure.

Thanks Ron, for explaining this to me, like I am a four year old, because I really needed it! Thanks Chris, for trying to explain this to me. I'm not too smart when it comes to the moped "top end". And thanks Jim, for chipping in the part about the head gasket! You guys are awesome! Swarm and Destroy!

Sincerely,

Chris Rice

Chris,

Ron's explanation is exactly what I was trying to describe. I guess I didn't catch onto the fact that you didn't notice the bearing (bushing, to be technically correct). Thanks for the help, Ron.

I machined my own (fortunately, I own a lathe), and they seem to be working perfectly on the two bikes I kitted.

Let me know how it comes out. Find a machinist to make you one out of bushing bronze. I could do it for you, but it is hard to do without the connecting rod and pin, because it requires some fine fitting. I machined mine to the correct inside diameter and I slightly oversized the outside diameter (with a very slight taper on one end so that I could start it into the hole). I then pressed it into the rod for a snug fit. I then took my 10 mm reamer and used it by hand to clean up the inside further (it seems that it changed slightly when pressing it in). I worked it by hand until the 10 mm wrist pin (the piston pin, or gudgeon pin) fit just right. Give these directions, along with the measurements (10 mm ID, 14 mm OD) to a machinist, and you should have no problem.

Chris S

I took off the head gasket and my bike got a huge power boost! I was doing about 36ish on flat after about a quarter mile. The chops look good too.

Ha. No problem.

sweet! that rocks..

yeah, adam (from the ten year lates) and i rode up to latonia the other day... it was a super nice ride... is that what you mean? isnt that rt 8? took about 20 minutes or so to get there.. super quiet, residential areas... kinda pretty.

we will ride this weekend... this rain is sucking it.

yeah, thanks anyways chris. Casey, I am not sure where latonia is, but I don't think so. Let's ride up that way this weekend and see where we end up!