You may use Cygnus 125 4 valves Cylinder kit to modify your RS 100 engine into 4 valves.
( RS100 オーバーサイズシリンダーヘッドキット-4V )
YAMAHA RS 100 Oversize Cylinder kit -4V
RS-090-4V-1 oversize cylinder kit : 194.76cc 4V
1. Cygnus 63.5mm ceramic cylinder with forged piston (80H)
2. Cygnus head 24/22 with rocker arms 26mm and pins
3. Cygnus camshaft T6 with stopper and gear
4. RS 61.5mm (7500 microns) crankshaft with A.L. gasket 1mm, stud*4 and chain
5. Cygnus valve cover cooling fins
6. Cygnus Tensioner and guide comp
7. Cygnus A, B shrouds and seals
8. Cygnus manifold
Need to bore KS to 67 for cylinder
Need to bore KS to 105for crankshaft
RS-090-4V-2:
1. Cygnus 67mm ceramic cylinder with forged piston (80H)
2. Cygnus head 25/23 (TD) with rocker arms 26mm and pins
3. Cygnus camshaft T3 with stopper and gear
4. RS 63mm (7500 microns) crankshaft with A.L. gasket 1mm, stud*4 and chain
5. Cygnus valve cover cooling fins
6. Cygnus Tensioner and guide comp
7. Cygnus A, B shrouds and seals
8. Cygnus manifold
Need to bore KS to 70.5mm for cylinder
Need to bore KS to 105mm for crankshaft
Change oil way
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additional items for RS 4V combo:
1. RS starter motor
2. RS 4V customized exhaust pipe
3. Carburetor PE 28mm, Thailand made
4. RS gear 14 gear or 15 gear
http://td87185162.blogspot.tw/2017/06/rs-4v-216cc.html