Zippy and Fred...I got the Grande running right!

Well, Saturday, I took my ped over to Matt's house cause he has the rack to mount peds on for maintenence. I took off my stock cylinder, piston and head and swapped it out. One major problem though...The piston doesn't work with my crank shaft. The diameter of the piston rod is too skinny for my crank shaft, hence lots of play, and no worky worky. So...I decarbed my stock piston and cylinder like zippy suggested, and put on a new base and head gasket. Now my Grande is running perfect. Plug chops are golden brown, and it is topping out around 33ish. I guess it was all the carbon, and the fact that I previously had no head gasket, causing a major vacum leak. As for the kit though...I am kinda pissed that the piston doesn't fit. Any suggestions on how to make it work? Or am I doomed to buy the malossi crank shaft to go with that piston?

Re: Zippy and Fred...I got the Grande running righ

Ron Brown /

Cris,

Talk to the people you bought th kit from.

Ron

Re: Zippy and Fred...I got the Grande running righ

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

Re: Zippy and Fred...I got the Grande running righ

P.S. What did you use for a head gasket? The Grande doesn't use one by original design.

CS

Re: Zippy and Fred...I got the Grande running righ

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.

Re: Zippy and Fred...I got the Grande running righ

Perhaps my response was confusing. Or, perhaps I misunderstood. The piston on many of the aftermarket kits comes drilled for a 10 mm wrist pin (the stock piston is 12 mm), and the pin is 10 mm OD. The bronze bearing in the connecting rod is 12 mm ID. What I did to solve this problem is machine a new connecting rod bearing (10 mm ID x 14 mm OD) out of bronze and I replaced the original with it. I was then able to use the new piston and wrist pin with the kit.

Chris S

Re: No head gasket req'd

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

Re: No head gasket req'd

Jim, All I know is that I put on a new base gasket and head gasket, and now my ped isn't running lean anymore...My compression is also okay.

Chris, I have never installed a new piston before and I am still confused about what you mean. Here are the parts that I am aware of, and what came with my kit...a piston, a pin that is hollow, that connects the piston to the crank shaft, and the c clips to keep the pin from slipping out of the piston. Is there another part that I am missing? The stock piston worked the same way. The hole in the end of the crank shaft is a lot bigger then the new pin that holds the new piston,(which is drilled to the same, smaller size). So...When I install it, there is lots of play, because the pin is smaller then the hole in the end of the crank shaft. Does that make sense? Sorry, but I am new at engine repair.

Chris Rice

Re: No head gasket req'd

Ron Brown /

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

Re: No head gasket req'd

Ron Brown /

Crisis,

I forgot, if your engine was designed to run without a head gasket, adding one will reduce power. This does not mean you don't have enough, nor does it mean your compression is not "good" as you percieve it. It does mean you have reduced the power output of your motor.

If you think the head will leak without a gasket, you should really grind the head or lap it to the cylinder. As long as you think your power is ok, you can wait til the next time you take it apart. It will not hurt anything.

Ron

Re: No head gasket req'd

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

Re: No head gasket req'd

Ron Brown /

Thanks Chris, I was not looking forward to those worms. : )

Re: No head gasket req'd

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

Re: No head gasket req'd

Chris, Why don't I mail it to you and then you could hook me up? That would be so cool. I will pay you.

Re: Zippy and Fred...I got the Grande running righ

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.

Re: Zippy and Fred...I got the Grande running righ

maybe it was the exhaust i traded you.. =]

super glad to hear it is running good though.. now you can ride with us again!

casey

Re: No head gasket req'd

Ha. No problem.

Re: Zippy and Fred...I got the Grande running righ

Dude, I took the day off yesterday and rode for like two hours. We all need to take a ride up route 8. You just take a left at the bottom of my street, instead of a right that we usually make to go toward the cov, or cincy. It follows the river and gets really rural. This dude at work was telling me about it. We should do it when the weather gets nice...

Also, Marcel is going to ship me a new 12mm piston and pin that will fit my stock connecting rod! I am also hoping that he will also ship me a new cylinder head with the decompression hole. Maybe you don't need it with the speed kit, in fear of losing compression through the hole, but it sure does make it easier to pedal start.

Re: Zippy and Fred...I got the Grande running righ

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.

Re: Zippy and Fred...I got the Grande running righ

I'd be happy to make the bushing for you. However, it looks like you have the problem solved with the 12 mm piston/wrist pin. Good job.

Chris S

Re: Zippy and Fred...I got the Grande running righ

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!

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