Three to four speed conversion vnb
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Member
1963 VNB4T
Joined: 17 Aug 2009
Posts: 49
Location: Athens, GA
Mon Nov 16, 2009 8:41 am quote
This is mostly a curiosity at this point, but I would like to know what is involved with a 3-speed to 4-speed gearbox upgrade. For some reason, it's hard to search for this topic on the forum. There's such a large gap between the gears on the 3 speed... I've casually thought about kitting the 125 at some point in the future and I've been reading all the different threads on this subject, but I feel like the 3-speed would limit the usefulness of making such an upgrade.
Enthusiast
Vespa p street racer / 1959 VBA / 1962 GS 160 mk1/ Crazy super cutown project/ 1969 Vespa GT p208cc
Joined: 27 Jan 2008
Posts: 55
Location: Orcutt
Mon Nov 16, 2009 9:39 am quote
Basically it is worth the effort. I am doing the same conversion on my VBA. You have to change the whole trans out. Gears, rear layshaft, christmas tree gear, clutch and shift box. Easy to do if you have the right parts and tools. I am building the VBA engine soon, if you want pics I can email them or post them here.
Ossessionato
1964 GS 160 MK II, 1967 Vespa GT, 1968 SS180, 1964 Vespa GL, 1964 Vespa VBB, 2006 Buddy 125, 2013 BMW C650GT
Joined: 07 Apr 2008
Posts: 2128
Location: Boca Raton, Florida
Mon Nov 16, 2009 10:21 am quote
Ears wrote:
Basically it is worth the effort. I am doing the same conversion on my VBA. You have to change the whole trans out. Gears, rear layshaft, christmas tree gear, clutch and shift box. Easy to do if you have the right parts and tools. I am building the VBA engine soon, if you want pics I can email them or post them here.
Post them here!

I like to watch!
Ossessionato
I have a few scooters....
Joined: 08 Nov 2005
Posts: 2015
Location: Long Island, NY
Mon Nov 16, 2009 11:01 am quote
Someone correct me if I'm wrong, but I believe the final output gear ratio is the same for both the 3 and 4 speed. It's the ease in getting to the last gear that makes the difference. If all you're changing is the gears, I say "Why bother". If your plan is to put on a top end kit, carb, and pipe, then I'd say "Maybe". It may be cheaper to go with a new LML 5 port engine. Just look at all the options before you make the jump.
Member
1963 VNB4T
Joined: 17 Aug 2009
Posts: 49
Location: Athens, GA
Mon Nov 16, 2009 11:30 am quote
For now, I'm just reading threads and daydreaming... if I use the stock motor, I would probably do the 2-port Pinasco 177 kit, appropriate carb and exhaust upgrade, and possibly move from the three speed to the four speed gearbox.

An alternative would be to store the vnb motor and use, say, a later super or sprint engine and go with one of the 3-port kits. I've been following the Pinasco 2-port thread that's near the top of the forum for ideas.

All this would be around a year from now, I'm just reading and learning this winter! But it would be nice to have enough power to be able to ride it out to work, or take my wife-to-be around town safely.
Hooked
64 Allstate 177 71 sprint veloce
Joined: 07 Nov 2009
Posts: 239
Location: idaho falls
Mon Nov 16, 2009 11:53 am quote
Killo is correct . When you're at the top of third gear it's the same as the top of forth . Anyway the older three gear dont have a big enough base to put a good cylinder kit on . Also you can cruise in second alot longer .
Addicted
'60 Allstate VNB1, '60 GS150 VS5, '61 Cushman VBB1, '62 GS160 Mk1 VSB1, '64 GL VLA1, '74 Rally VSE1 200 Euro, '78 P200e VSX, '06 LX150
Joined: 09 Nov 2009
Posts: 814
Location: Half Moon Bay, CA
Wed Nov 18, 2009 8:41 am quote
4 speeds for your VNB
I built up a spare for my '60 Allstate VNB1.

Started with a VBB, 4 speed engine. Kitted it with the same stuff as the VNB: 3-port 150, 20/20, p125 pipe.

I get the same top end, about 55, but nice to have that extra gear when I am riding the hills.

Jim Williams
Half Moon Bay, CA
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