125 aspirations

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125 aspirations

Post  Harlequim on Wed May 07, 2014 11:58 am

This will be my first scooter build so bear with me please...
I've a Vega frame and intend the build a 125 conversion. I have both starstream and Vega 75 complete casings, but understand the starstream don't fit as well with the back damper positions so intend to use the Vega ones. I've also got the Vega endplate

I've got a four speed gearbox inc Christmas tree and a Starstream crank. I've a few layshafts but think they're just 3 speeds, not been able to check yet. I understand I can mix in some more J range parts to complete the conversion

Now can someone help me out with a few questions:

1. Do I need a Starstream barrel, head and piston, or will a J125 model work?
2. A Vega exhaust will fit a J/Starstream barrel?
3. Are the Vega/J 4 speed gearboxes and layshafts one and the same/interchangeable? How can I identify which I have if they are not
4. What carb would I need- I think a Vega one works yeah?
5. Links to stockists of 1. 3. and 4.?

Any help on this would be greatly appreciated.

my email is footloose_doll@yahoo.co.uk

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Re: 125 aspirations

Post  Thackers on Wed May 07, 2014 12:43 pm

Hi. In answer to some of your questions
No1 you will need the head and barrel from a 125, I think standard bore is 57mm. I'm not too sure on the differences between a J 125cc (3 speed) barrel and a J 125cc Starstream (4 speed). They both have the same bore, stroke, cc and output/compression ratios. The J125 crank isn't an option (3speed). You will need a conversion piston, there's a seller on Ebay with TZR 150cc pistons @59mm bore or look out on Ebay for a Kawasaki KH 500 piston (a bit dearer but you can get oversizes) You will obviously need a re-bore and re-profile of the cyl head. Then get the barrel tuned you will need a 2mm packer under the cyl as the gudgeon pin height is different, CHECK your crank for the bearings, Chiselspeed do a Jap conrod conversion if it needs it
No2 I'm not too sure on as I have an old kegra pipe, but Chiselspeed do a leg burner pipe that works well on this conversion, Snails did have one for sale in that section on this forum  Very Happy Very Happy 
no3 I'm not too sure but you need the gearing from the 125 if not it will scream it's head off.
no4 Carb, I use a 25mm Dello'rto open belmouth
No5 Stockists, do your research for parts and don't forget the p&p as some charge more than others and it may save you to get several parts from one place rather than here and there.
As the conversion isn't run of the mill and the parts you need are rare be prepared to blow the budget (best not to have one) You have the hardest parts to find in that 125 engine especially the crank, my advice there if you post it send it with a value covered amount in case it's lost. They don't come up too often and when they do they're around £130 if memory serves
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125 Conversion

Post  trotsky on Wed May 07, 2014 3:53 pm

Hiya, Thackers advice is good if doing a 140cc Conversion, but if you are wanting a standard 125cc Conversion then

1. a J125 barrel, piston & head is fine. It all goes ok into a Vega casing.
  You'll need a 3 piece Mag set-up & the Cush Drive parts for the Starstream crank

2. a Vega exhaust will fit a 125 barrel, just a bit of fiddling

3. Vega & Starstream gearboxes are different, as are Crownwheels, Vega uses a bronze bush, Starstream uses a needle bearing. (They are not interchangeable)
Endplates vary also as on some, the 1st gear cog teeth on a Starstream box can hit the ends of a Vega Endplate I believe. 4 speed Layshafts are longer than 3 speed. Vega & Starstream ones are the same upto the rear hub bearing, but on the rear hub side, the Vega layshaft is splined upto the hub bearing, where as the Starstream layshaft is also splined on the end but has a flat in front of the hub bearing area to accommodate a hub cone similar to S3. If you use a J hub then you will need to use J wheel rims. J series Rear brake cams are longer than Vega ones.  

4. A Vega one would do, may have to re-jet. If you haven't got one, Chiselspeed do a nice small 21mm Polini arrangement using a modified 150 manifold & foam filter.

5.  Engine wise try Rimini Lambretta, as I have found Dean best able to source the harder engine parts (or a complete Starstream engine). Most other parts try Jem Booth, Scootopia, Rimini, Scooter Restorations (Great blow-up parts Diagrams), Jockeys Boxenstop, Chiselspeed, Armandos, K&S in Derby...& Ebay!!
Advice & help-on here, Scooterotica & LCGB Forums once it is back up & running.   

It sounds daunting & may take a while to source parts, but it can be done, but if you can come across a Starstream motor complete, life will be so much easier as it is pretty much a straight swap into a Vega casing. Most of this advice i'm sure is correct, but i'm happy to be corrected & others will input other advice as well...Good luck!!....Steve
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Re: 125 aspirations

Post  Snails on Thu May 08, 2014 3:48 am

One thing I can add for the straight 125 conversion is that apparently its better to use a cento barrel bored to 125 than a 125 barrel due to the exhaust port which on the 125 has a tendency to break piston rings. You have to cut the bottom off the cento barrel when doing this as the skirts are too thin. I did this on mine if you look at my topic on my resto. I got this advice from Jem Booth so I assume its correct - I dont have any first hand experience to back this up myself.
Also the exhaust port height is closer for mounting a Vega pipe.
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Re: 125 aspirations

Post  Weeks on Fri May 09, 2014 11:41 am

Never owned a Starstream / J range, Did they have an issue ref piston rings / exhaust port as standard ? or are you talking about a J125 barrel that has had the porting tuned/altered ?

No reason to doubt what you say ............. all I can add is I have used a J125 Straight conversion without issue both with standard pipe and old style Kegra.

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Re: 125 aspirations

Post  Snails on Fri May 09, 2014 2:34 pm

I can't remember exactly. I had the conversation with Jem about 7 or 8 years ago! I'm sure he would advise again if Harlequin asked.
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Re: 125 aspirations

Post  Harlequim on Sat Jun 07, 2014 3:35 pm

cheers folks, you're keeping up late at night with my research and manual reading ;-)
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Re: 125 aspirations

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