125CC Big Bore Setup

[dem0nk1d]

IÔÇÖve decided to build my old scooters engine from the ground up. This is going to be cleaned in and out, new bearings etc... So I decided while rebuilding the sucker I would go as big as possible. So I went out and ordered the following kit off line. Which is 125cc FM Ruima Stroker Bore Kit 55mm w/Head. The website that I ordered the kit from says this BigBore is going to need a stroker crank? WhatÔÇÖs a good crank setup to go with? Why can you not run this setup with the stock crank?

[SpyderMike]

your also going to need to bore out the crank case for the bigger crank to fit


i believe the bigger crank that you need is also made by Ruima and its 52.6mm stroke

and im not 100% sure on why you need a bigger crank w/ the stroker bore but im pretty sure it has something to do w/ port timing

[dem0nk1d]

yeah i know the case has to be cut for the crank. i need to find a local shop with a cnc machine to cut the case. also i think there is a .16 of gap you need. But before i build it, i want to get all the need information so i don't explode the facker.

[Wheelman-111]

Greetings

Given your recent issues with more-modest builds grenading, you have to ask yourself one question:

(Enter best Clint Eastwood imitation mode)
Do I feel lucky?
Well, Do Ya, Punk?

On those happy occasions when our experienced Hawaiian brothers grace us with their Wisdom, I have gathered that 125cc air-cooled Taiwanese setups are eminently Grenadable. Proceed with utmost caution.
Or a full wallet resting on a Devil-May-Care attitude.

[808BMW]

I wouldn't recommend a full stroker if you value your sanity.

I know what I'm doing and don't want one. They can be fast, and they don't instantly blow up, but they require WAY more maintenance than your normal modded dio motor. They need constant maintenance, a good tuner, and a willing owner.
That being said, strokers are fast, and can run just as well as any other bike, stock or modded. You just have to upkeep it more. Do a pre-ride check EVERY SINGLE TIME you ride, and keep extra parts/cell phone + friend with truck.
Honestly I'd save the headache and get a 72.

[dem0nk1d]

well might as well go for broke. i'll be documenting the build and possible grenading of the engine later..

but can anyone tell me why does it need to use the stroker crank? port timing sounds ligit, but i'm sure there is more to the picture.

[808BMW]

A stroker crank has a longer throw, or stroke. This in turn will push the piston higher/lower at each extreme of revolution, when compared to a stock crank (your piston will hit the head, and then drop too low in the cylinder).
A stroker bore will usually have a different wrist pin location on the piston, so when combined with a longer rod on the crank, everything is more or less where it should be at TDC/BDC.

I know a few guys that have stator problems on their stroker (they burn out a brand new stator within a month). Totally my assumption, but I say since the stator is designed to spin around X size circle at XX rpms, it now isn't correctly tuned to this new crank.
Then there are things like the fan shroud. You can shave down cooling fins on the head to fit the stock shroud (less fin = less heatsink to cool from). Or you can make a larger, custom fan shroud.

[z50r-ghost]

Good teachings, 808 - thanks for posting your experience and what you have heard and seen.

-i have ALWAYS heard that the 72cc setups are the way to go as far as daily-ridden reliability... imho, working on my scooter is just as fun as riding; but i love the fact that it is always ready to go when i am.

-jc

[maddog]

you can go with a fabrizi 82cc which is big bucks but quality, i built mine 20yrs ago and still have it= its not cheap and if google it some local boy is selling a 90cc version with pipe= this is an old school secret

[bakaracer]

The 55mm ruima bore you got requires the 52.6mm crank to work.If you bolt it up to your stock crank and case,the cylinder will not fit for one.The sleave of the cylinder is 58.5mm outside diameter so you will need to bore the top of the case to fit the cylinder into the case.If you run it with the stock crank,you won't get the full stroke needed to make the cylinder to run.You will be miss 11.2mm of stroke for it to run correct or at all.You will also need a big manifold and big carb,28mm minimum size and a stroker pipe for it to run its full potential.

[dem0nk1d]

so far i have the following
28mm OKO with jets
Performance Intake manifold
The 125cc Bigbore
waiting for the crack.


Then it's off to get everything else from weights to gears. You guys recommend a good gear combo?

Oh and whats the hype with the SYM/ZX trans I hear about.

[mr pibbs]

...The website that I ordered the kit from says this BigBore is going to need a stroker crank?

What website did you order from?

[dem0nk1d]

http://cgi.ebay.com/ebaymotors/125cc-NE ... arQ5fParts

2 more left 130 shipped

[bakaracer]

the sym/zx trans is for better topend because of the longer wider belt that is being used but your adding weight to the moving parts and the stock trans to me is about the same in speed wise.the stock trans is also way lighter so less weight in the moving parts result in better power.Thats why the indy car guys lighten everthing in the engine and make * of alot of power in such a small bore motor.

[veedubh20]

spree w/125cc . gas will be gone in few miles,. get a helmet