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Discussion Starter #1
I want a big bore kit. Im sure its like the XR/CRF 50s where you replace the piston and jug. Anyone know anything about the different ones and where you can get them?
 

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BORE KIT 150/160/180/200CC for Honda GROM / MSX125



The 57,25MM 150cc Light Bore kit is the Yuminashi starter set to tune up the MSX125 / GROM.
This cylinderset is developed in a multi-functional way because even if it's a light bore kit, it gives you a lot of possibilities later on.
As you can expect, the piston from the 150cc light bore kit is made to work in combination with the genuine 125cc head and valves and can be used in combination with the genuine single sensor MSX125 / GROM 25mm PGM-FI throttle body.
What you don't expect is that the piston is also able to be installed on the big valve Yuminashi SX30 Head with 30/24,5mm valves...
An other great feature from this kit is that you have the possibility to bore the 150cc light bore cylinder up to 160cc and even 180cc. You only need to buy the appropriate big bore piston set for the displacement you want and you can bore up your Light bore Kit to the displacement of your choise, you don't need to buy an other cylinder for that.
Please keep in mind if you bore the cylinder up, that you can't use the genuine 125cc cylinderhead anymore but need to install the Yuminashi SX30 Head.
The 150cc Light Bore cylinder comes in the original black color, and this is the only cylinder available in the Yuminashi assortment that comes in this color. All Yuminashi larger displacement cylinders come in an unpainted aluminum version to improve the cooling capacity.

The MSX/GROM 150CC LIGHT BORE KIT includes:


  • 1 x 57.25mm Aluminum cylinder
  • 1 x 57.25mm Light Bore Piston
  • 1 x 57.25mm Piston ring set
  • 1 x Piston pin (13mm)
  • 2 x Piston clip
  • 1 x 57.25mm special Copper Head gasket
  • 1 x Cylinder base gasket
PRODUCT CODE: 12103-K26-572A
PRICE: 8.224THB (221.00€) Exclusive V.A.T.

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BIG BORE KIT 160CC
░ FOR HONDA MSX125 / HONDA GROM (USA)



● The Yuminashi Big Bore Series are mentioned to be used in combination with the genuine MSX125 / GROM crankshaft and crankcases.
The limit for competition is in many countries 160cc, so the Yuminashi R&D has made this 59,25mm kit with 159,56cc to meet the rules about he maximum displacement.
The 160cc Big Bore kit can't be installed in combination with the genuine cylinderhead, but need to be installed with the Yuminashi SX30 Head which has special 30/24,5mm stainless anti magnetic valves and titanium alloy retainers with double progressive and reinforced valve springs.
The Big Bore kit comes in a non painted aluminium version to improve the cooling capacity from the cylinder and can be bored up until 180cc.

The MSX/GROM 160CC BIG BORE KIT includes:


  • 1 x 59.25mm Aluminum cylinder
  • 1 x 59.25mm Light Bore Piston
  • 1 x 59.25mm Piston ring set
  • 1 x Piston pin (13mm)
  • 2 x Piston clip
  • 1 x 59.25mm special Copper Head gasket
  • 1 x Cylinder base gasket
PRODUCT CODE: 12103-K26-972B
PRICE: 8.344THB (225.00€) Exclusive V.A.T.

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BIG BORE KIT 180CC
░ FOR HONDA MSX125 / HONDA GROM (USA)




● The Yuminashi Big Bore Series are mentioned to be plug & play in combination with the genuine MSX125 / GROM crankshaft and crankcases.
This 63mm bore kit is with 180cc the largest displacement possible to be installed on the genuine MSX125 / GROM crankcases without modification.
The 180cc Big Bore kit can't be installed in combination with the genuine cylinderhead, and need to be installed with the Yuminashi SPR-X Head which has special 33/26,2mm stainless anti magnetic valves and titanium alloy retainers with double progressive and reinforced valve springs.
The 180cc Big Bore kit comes in a non painted aluminium version to improve the cooling capacity from the cylinder.

The MSX/GROM 180CC BIG BORE KIT includes:


  • 1 x 63mm Aluminum cylinder
  • 1 x 63mm Light Bore Piston
  • 1 x 63mm Piston ring set
  • 1 x Piston pin (13mm)
  • 2 x Piston clip
  • 1 x 63mm special Copper Head gasket
  • 1 x Cylinder base gasket
PRODUCT CODE: 12103-K26-630B
PRICE: 9.304THB (250.00€) Exclusive V.A.T.

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SUPER BORE KIT 200CC
░ FOR HONDA MSX125 / HONDA GROM (USA)




The Yuminashi 200cc Super Bore Kit is based on our racing experience with the very powerfull and exclusive Yuminashi SP200R factory engine.
If this limited edition engine slipped true your fingers back then, then you have the chanse now to buy the powerpack from the Yuminashi SP200R engine with the 200cc Super Bore Kit for MSX125 / GROM in combination with the big valve SPR-X Head (33/26,2mm valves).
Keep in mind that the Yuminashi Super Bore Kit's are mentioned to be installed on the Yuminashi Super Bore crankcases. These crankcases are available for MSX125 / GROM in a electro starter version and a kick starter version.
You can also bore your genuine crankcases up, but to make things less complicated Yuminashi have added the plug&play ready Super Bore Crankcases set to the assortment which comes in an aluminium, non painted version to improve the cooling capacity and to make it easy for you to install all Super Bore Series cylinder kit's.

The MSX/GROM 200CC BIG BORE KIT includes:


  • 1 x 66mm Aluminum cylinder (Non painted aluminum to improve the cooling capacity)
  • 1 x 66mm Light Bore Piston
  • 1 x 66mm Piston ring set
  • 1 x Piston pin (13mm)
  • 2 x Piston clip
  • 1 x 66mm special Copper Head gasket
  • 1 x Cylinder base gasket
PRODUCT CODE: 12103-K26-660B
PRICE: 9.304THB (250.00€) Exclusive V.A.T.
 

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Discussion Starter #3
Know anything about that company? Anyone know the quality of that kit?

Thanks!
 

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Don't know much as the brand isn't popular in north america. That is the only option for a bore kit on the GROM though.
 

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either these bore kits are very new and no one has really had a chance to do a built and document it on the net or im having a tough time trying to find MSX125 builds with these kits.
 

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yuminashi is known for their sp200r engine, but his products look to be well made. Im currently working on getting an sx270 cam, 150 light bore kit and the progressive dual springs for my bike from rz racing in the netherlands. At the moment only the 150cc kit is available. The sx30 head is still being tested the last i heard. The prototype should have been tested by now and they are most likely working out any bugs and getting ready for scale production. I am guessing we will hear more soon and the pictures of the heads should be posted shortly. Up power in france also is a distributor.
 

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yuminashi is known for their sp200r engine, but his products look to be well made. Im currently working on getting an sx270 cam, 150 light bore kit and the progressive dual springs for my bike from rz racing in the netherlands. At the moment only the 150cc kit is available. The sx30 head is still being tested the last i heard. The prototype should have been tested by now and they are most likely working out any bugs and getting ready for scale production. I am guessing we will hear more soon and the pictures of the heads should be posted shortly. Up power in france also is a distributor.
sure sounds like what is going on at the moment, I guess the original pictures we all saw on their websites and here were prototypes fresh out of the CNC machine and paint booth? or maybe some really good renderings?
 

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I am guessing the kit is relatively new and noone has actually installed the kit or figured out the tuning for it yet.
 

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Anyone know what kind of realistic improvement in performance one can expect from a bigger bore kit like the 180 or 200? Worth voiding the warranty over?
 

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worth it is up to you.

For some any additional power is worth it.

hard to say exactly how much power gains. depends on the tune and other modifications.
 

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Anyone know what kind of realistic improvement in performance one can expect from a bigger bore kit like the 180 or 200? Worth voiding the warranty over?
how i see it if you have the cash to do crazy mods like that to a grom you shouldn't worry about warranty. and i doubt many people will be waiting for warranty to expire and then do mods. might as well hack into the bike when you are ready no matter how soon it is
 

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how i see it if you have the cash to do crazy mods like that to a grom you shouldn't worry about warranty. and i doubt many people will be waiting for warranty to expire and then do mods. might as well hack into the bike when you are ready no matter how soon it is
True, but I wouldn't void the warranty over a minimal performance enhancement (like an additional 5 mph on the top end, for example), regardless of how much disposable income I have.

Cosmetic mods, on the other hand, I plan on doing on day one.
 

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It's personal preference.

I don't care much for the warranty on the GROM.

It's not a very expensive bike so I'm not too concerned about things blowing up.
 

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Discussion Starter #14
On a crf50 they are 2.5hp stock and weigh 110lbs.
The Grom is 10hp and 220lbs.

An 88cc big bore gives you 4-5hp. HUGE difference!
A 108cc stroker makes like 8-9hp and is RIDICULOUS!

Adding a small big bore kit on the Grom would make a significant difference and in my opinion be worth voiding the warranty.
My 50 with the 108cc is too much. I actually took the motor out and use the 88 instead. Too much torque and too twitchy when trying to ride wheelies. We don't know if we really want a 200 kit, might make it unstreetable.
A mild bore kit, exhaust and GEARING would be sweet for me.


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I want power!!! I was thinking about swaps etc. trx450r motor anyone? LOL



As much as that would be awesome it would be insane. I will likely do a big bore kit, just dont know how big I want to go.

Stew
 

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what size bore kit to go with is an issue especially if you want the bike to not be some stupid powerful bike where you have to start considering downgrading.
 

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The engine has been used in the Innova scooter for close to a decade. The stock head is heinous. Tiny ports and valves like a CRF70. Stock power peak is around 7500RPM, and adding bore won't help the revviness.
 

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Discussion Starter #18
Have you heard anything about new motors or parts for these? Like Piranha or any other brands?


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Have you heard anything about new motors or parts for these? Like Piranha or any other brands?
Piranha isn't likely to get in the Grom market, but there are others.
I'm hoping to see one with the clutch cover off to verify crank end, maybe when some one is getting a sling lightened, to see if the 65mm stroker from the ANF is a drop-in.
 

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Discussion Starter #20
I wouldn't mind keeping the stock motor stock, and dropping in a motor instead. Assuming pricing is similar to fiddys
 
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