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  • Full Essential Big Bore Kit for Honda SH125i
RRP: $583.28
$545.24 (You save $38.04)
3,240.00 Grams
Usually ships in 1 week
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Minimum Purchase:
1 unit(s)

 Product Description

● 164CC ESSENTIAL POWER PACK (SH125 ESP / 13MM PISTON PIN) buying-2-free-shipping.png

● The 164cc Essential Power Pack includes all essential parts to transform your SH125 in to a larger 164cc version with as result, a seriously improved acceleration and top speed compared with a stock SH125 and SH150.

All parts in the kit are plug & play and easy to install. Normal motorcycle / scooter mechanical skills are required, and with the deeper valve pockets in the 60mm piston we recommend to set the valve clearance at 0.05mm intake valve / 0.08mm exhaust valve.

● The 164cc Essential Power Pack for SH125i includes the Yuminashi 60mm 164cc Flat Deck Cylinder Block which is pure racing DNA from the YUMINASHI PRO-SERIES, mentioned for a 125 engine with stock 125 head.

The Flat Deck Cylinder Block has been developed specifically for high performance engines, so while developing this cylinder the R&D from the Yuminashi Racing Department had 2 important aspects in mind; the cylinder had to be leak free in combination with a high compression piston, and the material from the sleeve had to be improved compared to stock Honda to avoid ovalization from the cylinder with an aggressive driving style in mind.

A larger water/coolant capacity has also been worked out with the eye on a cooler running engine in combination with a high compression piston.

The result is that with the flat deck design and in combination with the copper gasket you are actually able to run the higher compression ratios without the fear of leaking head gaskets and with developing an entirely new very hard cylinder sleeve ovalization, oil leaks and compression loss are avoided!...   


● The 60mm 164cc Yuminashi Light Bore piston set with 13mm piston pin comes with the Essential kit and is specifically designed to be used in combination with the stock 125cc cylinder head.

The piston set in the kit comes complete as you can see below with the piston, piston rings, 13mm piston pin and the 2 piston clips.


The piston rings are treated with a hard chromium plating layer (Cr) which has excellent characteristics which combine the original properties of chromium metal with the advantages of erectro-deposits. 

The main features of hard chromium plating are as follows:

1. Extermely high hardness of HmV (Micro Vickers)
800 to 1100 (cf. gray cast iron 220 to 270)

2. High melting point of approx. 1800°C
(cf. cast iron 1200°C)

3. Good thermal conductivity and corrosion

4. Low friction factor and excellent wear resistance.
Such features are very effective in preventing
piston ring wear.


● The special copper 0.3mm gasket set , 60mm for eSP 125cc head high compression engines (164cc kit) comes with the kit to make the perfect seal.

The copper head gaskets have a much better sealing characteristic compared to the stock material used to produce the stock head gaskets which makes the copper head gaskets the preferred gaskets for engine tuners with high compression big bore setups.

The reason why all Yuminashi big bore kits are coming with the full copper gaskets sets is because Yuminashi knows that the one thing no engine builder wants to worry about is a head gasket failure. Stock head gaskets hold up well enough under normal loads. But as compression ratios and combustion pressures go up, a stock head gasket may not be able to maintain a leak-free seal. And once hot combustion gasses start blowing past the gasket’s combustion armor, bad things begin to happen. The combustion armor cracks or burns through, compression is lost and the gasket fails. Or, oil start finding new ways to circulate inside the engine, often with negative consequences.

For many years, serious racers have considered copper head gaskets to be the hot setup for high horsepower engines and most top fuel dragsters and funny cars run copper head gaskets because nothing else works.

Therefor, all Yuminashi big bore kits like this 164cc Essential Kit for SH125i come complete with the full copper head gaskets in the box to make sure your head gasket will be able to make the perfect leak-free seal..


● The 31mm throttle body upgrade is essential to take the full potential out of your 164cc kit, even if you have the original 125cc cylinderhead with 27/22mm valves and would think that this doesn't make much sense.

The result from a 164cc Light Bore with this 31mm PGM-FI upgrade set installed is amazing with an improved acceleration and higher top speed as result!....

The first generation throttle body is superseded since November 15, 2017 with the new 2018 model which has a new stainless steel bracket/cable holder to make a perfect install possible on any PCX125/150 and SH125/150i. 

The venturi is just like the first generation machined in to a stack to create an optimized velocity with ram air filling effect, and the set is Plug & Play ready to accept all your genuine SH125/150i - PCX125 V1/V2 and PCX150 V1 throttle body sensors. 


● The 8-Holes Low flow injector (B-Type) comes with the kit to compensate and balance the higher volume of air which is sucked in by the large piston with the help of the 31mm throttle body... 


● The larger manifold set in the kit comes with the correct rubber installed to accept the 31mm throttle body, and the 8-holes B-type injector.


● The Yuminashi double valve spring & retainer set comes with the set to avoid floating valves in combination with the higher lift and duration camshaft.


● The YUMINASHI Billet CNC X250 8.6 Camshaft Kit in the kit is the hot ticket for getting the most out of your SH125i.

Yuminashi camshafts are designed in conjunction with our racing efforts, and in turn the design gets passed down to our customers for the best power gains.

Yuminashi R&D designed this camshaft to be used in combination with the stock 125cc valves, with a increased lift and duration to produce a potent curve with solid torque to red-line. 

● The stock SH125i 12.95mm roller diameter is adequate for all stock camshafts, but high performance engines with high lift camshafts benefit from larger diameter rollers for the simple reason that the larger face of the 16.9mm rollers accept a more aggressive lobe profile before the roller digs into the cam lobe, which of course leads to nearly instant camshaft failure.

Therefor the rocker set with larger, more durable rollers comes together with the camshaft and the 164 Essential Kit as a complete set to ensure increased durability and reliability.


● The special larger adjusting screws (SPL) come with the kit to ensure a plug & play experience in combination with the higher lift camshaft.  


● The CR10EK Nickel Multi-Ground spark plugs have been tested in combination with the Yuminashi 164cc light bore & big bore kits and come with the Essential Kit because it resulted in a powerful cooler running engine.

The Multi-Ground Electrodes Improve Ignition Capabilities and are Less Sensitive to Increased Voltage Requirements Due to Gap Growth.

Designed to Specific Manufacturer Ignition Requirements, NGK's Multi-Ground Plugs Maintain All the Features of Their Standard Plugs, Including:

• Corrugated Ribs to Prevent Flashover
• Pure Alumina Silicate Ceramic Insulator, Providing Superior Strength and Better Heat Transfer
• Copper Core to Aid in Heat Removal
• Triple Seals to Prevent Leakage


● Once the 164 Essential Kit is installed you will run a higher compression ratio compared to stock.
Because a high compression engine always has a higher combustion chamber temperature than a stock compression engine, it's always a good idea to tune the cooling capacity from your engine together with the performance from your engine. If you don't balance this out, then it's possible to run in to an overheating engine.

A simple device like this 1.6 High Pressure Radiator Cap comes with the Essential Kit to help you to raise the boiling point seriously from your coolant and avoid your liquid to turn in to steam.

To understand this we need to give a short word of explanation about coolant (antifreeze) and the role of radiator pressure in general...

Please open this link to read all details concerning the role of the radiator pressure and the 1.6 bar radiator cap which comes in the Essential Kit.


● The 164 Essential Kit comes with the 12 gram Payu Japan roller weights to get the right balance between acceleration and top speed.
The stock roller weights are too heavy, even for a 164cc kit and installing these 12 gram roller weights in combination with the stock SH125i variator result in a remarkable difference. 


● The 164cc kit sucks in a lot more air compared to stock, so installing the correct intake diameter is really essential to get the full potential out of your engine.
With the Big Tube Air Intake set in the kit you have the right diameter which the engine needs. Keep in mind that you will need to make the opening larger in the stock air filter box to install the larger Big Tube Air Intake set.


 We recommend to install the Silent Sport exhaust from our Takegawa colleague's in combination with this kit, to get the full power potential of the kit.

Free worldwide shipping with DHL Express is included in the price quotation!...

(**Exception for Russia, Brazil, Portugal, Canary Island and French Polynesia, they will be served with free shipping by the Express Postal service)


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