Modern Vespa

I appear to be leaking form my head gasket on my GT200. Gonna do it myself but can't find much info or tips on the procedure.

Awesome

Worth doing? http://www.ebay.com/itm/Malossi-Cylinder-Kit-GT200-GT-Vespa-Scooter-/271290433151?pt=Other_Vehicle_Parts&hash=item3f2a2b7e7f&vxp=mtr

If you're just doing the cylinder, the Polini kit 140.0201, is about $50 cheaper, and pretty much the same quality. If you are going to go Malossi, you might as well go the whole way with the top end kit 3113914, with head and cam, while you're in there.

I have a good thorough thread on all the upgrades I've done on my scooters... The beginning was when I first got my GT200. I have listed all the parts I installed, and my thoughts.

I wouldn't go with the polini cylinder, instead go with the malossi. The reason for that is detailed in the thread... See here https://modernvespa.com/forum/topic90581?highlight=

Any further questions after you read that, feel free to ask away.

cool cool cool

I read the thread about blowing up two 200cc Leader motors previously, and what I came away with was not that one performance brand is better than the other, or that if something happens to one person using a product, it will happen to everybody who uses it, but that it really was a learning experience for everyone involved that unfortunately ate through two very expensive engines. If I had to guess, based on the entire thread, I would say that the cracks which you attributed to a manufacturer defect were in fact a symptom of overheating and a lack of lubrication, which also led to the failure of the second motor. Had you split the cases before throwing a new top end on it, you might have seen signs that the second engine would also fail. I learned the hard way when I was 16 that you can't make a CB350 as fast as an RD350, and went through two very expensive (at the time) top ends before I completely destroyed the bottom end and moved on to more displacement. Had I posted a thread about it at the time, it would have read very much like the one about the GT200.
I personally favor Malossi, mainly because of the depth of their Maxi Scooter catalog and what they have done with the T-Max, but the vast majority of people who install either cylinder kit by itself experience a different end result than you did, and in the grand scheme of things, neither kit is "better" than the other. If you just want to throw a bigger jug on your Scooter, either of them is fine, and the Polini is cheaper, if that's a factor. But if you want to build a complete motor, Malossi offers a lot more potential. There is a lot of great information about building Leader and Quasar engines that stay together on some of the Aprilia forums.

Why not go OEM? Is it more expensive?

The second post is not a GT200L.

What head gasket? Are you talking about the cylinder head gasket? You could easily just buy a gasket for about $38 from Piaggio. Replace it and you are good to go.

I was just thinking about putting on a kit just to get a little more out of it. Also, I've watched the video and just assume that it has to be pretty much the same as talking apart the top end of a GT200. I guess my only question would be: Without a cooling fan, how to you find TDC on the compression stroke? Take off the side case and turn the pulley by hand using a TDC tool?

I certainly misconscrued your OP. Please disregard.

pro tip: align the motor to TDC as verified by the timing mark on the crown wheel (at 4V obviously) and the stator/water pump marks. verify that the piston is indeed at TDC with a tiny screwdriver or whatever probe device you so desire.

then, clean the crown wheel and chain with some brake clean and MARK THE CHAIN AND CROWN WHEEL WITH A SHARPIE IN NO LESS THAN THREE PLACES-- think like 9-12-3 kind of situation.

sorry for yelling... but yeah, this will save you HOURS of BS'ing around when you go to put it all back together.

when you pull off the cam decompression counterweight you'll need to rotate the crank a few degrees to clear the head-- this is best done off the crank nut. the counterweight has a small plastic buffer, don't lose this (or the spring) down in the motor. it's not a deal breaker, but they're both a bitch to fish back out-- stuff some blue shop towels in there to prevent it.

other than that: clean everything meticulously, remember to put the centering dowels back in place along with the sealing o-rings on the studs and properly torque everything down.

best,
-greasy

I'm gonna go out on a limb here, but I think my very worn out exhaust gasket might have had something to do with my head gasket taking a crap.

It won't have helped your exhaust valves either.

Ok, I finally put on the new head gasket and got the head back on, but even though I sharpie marked the chain to the 4V arrow and I'm sure I was careful not to let the bottom of the timing chain slip off the crank, I seem to be off a tooth the top mark that's on the head. Just make sure the timing mark on the the water pump hole is good and move the chain over so the 4V arrow lines up with the index mark on the head?