OP
Fri, 10 Oct 2008 03:18:38 +0000

Ossessionato
'10 GTS 300 Super, '79 Vespa P200E, '04 Vespa PX200, 2011 SportCity 300 Cube [Sold]
Joined: Thu, 07 Sep 2006 02:00:48 +0000
Posts: 2923
Location: San Francisco, CA
 
Ossessionato
'10 GTS 300 Super, '79 Vespa P200E, '04 Vespa PX200, 2011 SportCity 300 Cube [Sold]
Joined: Thu, 07 Sep 2006 02:00:48 +0000
Posts: 2923
Location: San Francisco, CA
Fri, 10 Oct 2008 03:18:38 +0000 quote
Hi all,

I am looking at a Vespa P200, which is in decent shape body wise and seems like a good deal.

One thing that has me concerned - supposedly the previous owners ran the scooter very lean, which resulted in a blown piston. I guess it blew a hole in the top of the piston head. To fix this, the guy rebore and got a new piston, so the engine is now technically a 205cc. What do you guys think of this? Is this a big deal? Will this affect performance in bad/good way? Perhaps this won't matter if I drop in a kit?
Fri, 10 Oct 2008 05:43:15 +0000

Destroyer of Worlds
LML Star 125, Vespa GT200
Joined: Mon, 13 Aug 2007 07:35:32 +0000
Posts: 2011
Location: London, United Kingdom
 
Destroyer of Worlds
LML Star 125, Vespa GT200
Joined: Mon, 13 Aug 2007 07:35:32 +0000
Posts: 2011
Location: London, United Kingdom
Fri, 10 Oct 2008 05:43:15 +0000 quote
If the job was done right, nothing to worry about.
Fri, 10 Oct 2008 07:31:38 +0000

Molto Verboso
Vespa 50 Special '71 / Vespa 150 Sprint V '78
Joined: Tue, 20 May 2008 13:24:38 +0000
Posts: 1347
Location: Europe
 
Molto Verboso
Vespa 50 Special '71 / Vespa 150 Sprint V '78
Joined: Tue, 20 May 2008 13:24:38 +0000
Posts: 1347
Location: Europe
Fri, 10 Oct 2008 07:31:38 +0000 quote
thefuzzylogic wrote:
If the job was done right, nothing to worry about.
Yep a rather regular job having an old cast iron cylinder a slightly larger bore and a oversized piston
Fri, 10 Oct 2008 12:42:18 +0000

Moderator
1965 Vespa SS180, 1963 Lambretta LI150
Joined: Mon, 05 Mar 2007 14:05:05 +0000
Posts: 6980
Location: Detroit, Michigan
 
Moderator
1965 Vespa SS180, 1963 Lambretta LI150
Joined: Mon, 05 Mar 2007 14:05:05 +0000
Posts: 6980
Location: Detroit, Michigan
Fri, 10 Oct 2008 12:42:18 +0000 quote
remember that the displacement of the engine ( 205cc ) is just a simple multiplication of the bore (width of the cylinder opening) times the stroke ( distance of travel ).

The stroke will stay the same as long as you use the same crankshaft / conrod ( you'll hear sometimes people putting on a "long stroke crank" on a tuned engine, to gain more displacement ).


Oversize pistons / bores on scooters is no big thang, as was previously mentioned.

I think the 20th oversize on an SS180 is a 200cc ...so it's a common conversion for people to bore it straight out to that, and drop in the big piston for the added displacement.

Lambrettas, too ... many people will bore out an LI125 or LI150 jug to 175cc specs, and run an oversize piston to basically make it an LI175. ( the TV175 has a longer stroke con rod, so if you continue to use the LI-style crank, you have a shorter stroke but a wider bore to come to the same displacement.

Simple math. Make sense?

In any case, proper gapping of the new rings and a well-performed break in period make all the difference.
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