Upgrading from 50cc to 70cc.

[drawkward]

I'm sure there are YouTube videos outlining the basic principles about scooter engines... I was just curious if you guys had any pointers and side info. Things like - pin size, plastic shroud removal, coil install - purchase, cylinder prepping and oiling, gasket removal... I'm a noob to engines - I am your student.

[2strokd]

Its good to make sure everything is covered and your ready to tackle the job, props for that .
As far as piston pin size, that mostly depends on the year of your scooter. If its an 03 or older it probably has a 10mm pin, if its 04 or newer probably a 12mm pin. The only way to be sure is to pull the cylinder and check. A theory Brent had thought about was that if the vari shaft or crank output shaft was 13mm you had the 10mm pin and if you vari shaft was 16mm you had a 12mm pin.
When i picked up my last motor we had to rule this out .
Its an 03 model with a 16mm vari shaft and a 10mm piston pin.
I really dont know of any other way other than taking it apart and looking, or maybe compare yours (model, year, etc) with others that have taken theirs apart and know the piston size.
Even then i wouldnt be 100% sure until i saw the piston myself.

By "plastic case" are you speaking f the fan shroud around the engine? If so,its held on the case by two phillips screws on the exhaust side. It might have another holding the two halfs together. On the other side below the carb you will see were the cover pushes into two rubber mounts, it will pull right out of them.

The coil is straight forward. Two bolts and a couple of wires. If you have worked on your cvt i know you can tackle this

Just wipe a thin coat of 2cycle oil on the piston and inside the cylinder. Make sure you get the piston pin and bearing well also.

Any old gasket left can be scraped of with just about anything, just make sure to be carfull not to scrape too hard and nick or gouge the case.
If the stock fuel system is working correctly you shouldnt need to modify it for a big bore.

[90GTVert]

I really need to do a complete BBK upgrade how-to or guide, but I haven't had a BBK to do lately. Hopefully I can put something together when I do one of my engines.

Here are some links I already have put together that may be of interest :

49ccscoot.com/smooth.html
49ccscoot.com/disass.html
I started to do a little guide here, then hit a snag lol...
49ccscoot.com/bigbig.html

To address your more specific questions...

Wrist pin size : If the Strada is like the Vento, any model past 2003 or 2004 should have a 12mm wrist pin. Models eariler than that should be 10mm. It seems that in most (not all) of these engines the diamter of the splines on the crankshaft (where the variator rides) can be an indicator of wrist pin size. Cranks have either 13mm or 16mm splines. The 13mm splined versions tend to have the 10mm pins, and the 16mm splined cranks tend to have 12mm pins. The only way I know of to be 100% sure of what you have is to pull the engine apart and measure the wrist pin. It should either measure 10mm or 12mm in diameter.

Opening the plastic case (engine shroud I assume), is pretty simple. There are bolts on one side to hold the fan cover on. Remove those. There should also be a screw that secures the fan side cover to the cylinder cover. Remove that. Then you can separate the fan shroud from the engine shroud. Then pull gently outward to free the engine shroud. Of course you need to remove the spark plug wire to do this.

Coil Install : Also simple. The hardest part of the coil installation on one of these is usually getting all the fairing off to reach the coil. Once you can reach the coil it will either have a harness or a couple of wires to unplug. Then you can remove the spark plug wire and unbolt the coil from the frame. Mount the new coil to the frame. Attach the wires if you can. If not, you may need to cut off your harness or existing terminals and add terminals that will fit the new coil. Some coils only have one terminal. If that's the case, attach the ground wire to the mounting location on the frame using a ring terminal. Positive will go to the coil's terminal. Attach the spark plug wire and try it out.

Oiling the cylinder : Smear a little 2 stroke oil on the cylinder walls. Apply 2 stroke oil to the piston and rings before you slide them in.

Gasket Removal : Peel the old gaskets off with a gasket scraper or razor. Just be very careful not to scar the case or whatever you're removing a gasket from. Put rags in the crankcase to prevent gasket pieces from falling in there during removal. If necessary you can use a scotchbrite pad to finish the surface. I use brake parts cleaner on a shop towel or rag on the gasket surface as well.

Fuel line/vacuum prep : I don't really do any. If everything is working well, a few cranks or kicks should get fuel on it's way to the carburetor.

EDIT : It seems 2strokd and I were typing our long replies at the same time. lol I had to walk away for a bit to take care of some stuff in the middle of mine .

[2strokd]

Very nice Brent lol

[90GTVert]

At least he should feel safe getting the same info 2x from different sources. ;D

[drawkward]

Before reading this, all those things seemed so complicated. Now it just sounds like a couple of bolts here and there... Just another easy step by step job - You both have really simplified it. Thank you!

A good Big Bore Kit installation tutorial would be awesome! I can attempt one when I get my BBK, but at this point I don't really feel as confident as you probably do - you've taken apart your scooter and engine multiple times, I'm sure.

Maybe I'll try a little video, wipe the dust off the old cam and tripod.