O-tuning V5A for my elder son (hot french recipe inside)

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fastfrog
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Hi folks back to the bench with a new project: building my elder son first vespa. He is close to 15 and really deserves her. I mean it. A nice boy, brilliant at school, no drug nor R'nR; I found a V5O in a rather fecking condition but with the precious V5. Complete resto and safe full hydraulic conversion scheduled.
He wants her in a deep black rendition.
For the engine I found a 50 with a 4 gear box. No sign of bad treatment but obviously engine has been previously upgraded with a kit (case ported).

My goal is to give him a close to standard engine with more guts and fun to ride. So let's go for a o-tuning session. No kit or unaffordable special tuning part. French pig became awful mutterficker, so discretion and original specification are much appreciated....
Standard timings are:
T: 94°
E:134°
I: 90+40= 130°
guess what? Those timings are very close to those on a standard Solex: A pain....

with a 2,5mm packer I'll get:

T: 114°
E: 158° with a small grinding amount (1,5mm up)
BD:22°
I: 150°
very conservative timings indeed. But quite enough for a newbie on the vespa scene.
I keep the SHB 16/16, standard air filter and a banana exhaust. Siproad banana is too expensive and high Rpm tuned to match a so small and torqueless engine.

delivery service:

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a standard 38,4mm barrel with its 2 obstructed main ports and exhaust as small as your thumb tip. Broouuu, that sucks a lot...

Barrel is ready for a boost port conversion. The 2 ring pegs leave only place for one large port, no way to get 2 boost ports there.

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beginning of the digging job:

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exhaust port cleaned up a bit:

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Slightly nicer:

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A bit more difficult: digging a boost port each side of the exhaust
Keep in mind that the thickness of the wall is 5,5mm no more....

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Moviluty is your friend:

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crank obviouly finely balanced!! a shame.

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After a little operation it gives 105-45=150°

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This pic shows perfectly the main prob with this small bore cylinder: a huge step is facing the gaz flow in its way up to the transfert: Pas bien du tout!

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better!

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slowly things are looking better:

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last step:

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Last edited by fastfrog on Tue Mar 31, 2015 10:39 pm, edited 2 times in total.
Size matters!
Norrie Bodge
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Unreal work again FF
bet the lad can't wait for it all finished ;-)
eden
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that's a lot of grinding :)
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fastfrog
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Norrie Bodge wrote:Unreal work again FF
bet the lad can't wait for it all finished ;-)
He is learning patience too!
Size matters!
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T5-190
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Very nice work.
dave411
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A work of art
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wack 63
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Very nice work but why not balance the crank with big end at 12 o/clock?
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fastfrog
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Too much matter to be removed the opposite side or Densimet to be put. Too expensive and on a so small capacity engine that sounds useless at this step of tuning.
Size matters!
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fastfrog
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new oversized piston arrived yesterday and I had an unpleasant surprise at the box opening with the pegs located near the exhaust right in the middle of the 2 boost ports. I'm good for a little change...
Size matters!
tony172
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clever git ;)
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