70cc extreme 1e40qmb chinarelli budget build

[lokstar]

Hey guys, been lurking here all the way from Australia for years now and picked up a wealth of knowledge. So thank you all for your freely shared info.
I slapped a Chinese 70cc kit (as it came/ untouched) on a 1e40qmb with a little cvt tuning a few years ago for a mate and 6500km later it’s still going strong regularly used for 80kph, 30-40 min rides.
I’m now planning new build on another scoot of the same model.
Below is my plan/recipe/parts list (most of which I already have) and I’m pretty handy with the tools, carb/cvt tuning and have decent selection of machining equipment so nothing within reason is out of the question.
The main goal of this build is making the most out of the cheapest accessible parts with NO performance brand name parts! for high revs and short runs, rideability and longevity are not of concern.
Any educated advice or experienced feed back would be appreciated.
Thanks👍

- Model: vmoto monza 1e40qmb (stock crank with 12mm wrist pin)
- Chinese 47mm 70cc AC cylinder
- 1.6mm cylinder spacer (1x .9mm automotive sheet metal spacer + 2x compressed gaskets) to bump durations of big bore cylinder from 178/118 (No gasket was used to measure that) to approximately 189/130
- Machine down the cylinder top/deck in my mill to rectify piston/deck height.
- Re shape/widened ex port to 72% of bore with a flatter/wider ex roof (not flat!) for more blow down area.
- All ports cleaned up/chamfer filed
- Ex and Trans port floor heights will be left untouched (as I don’t have a 90* Dremel attachment
- recut the stock head on my lathe to match bore and piston crown (for a proper squish band around 50% of bore)
- .5-.7mm squish (10-15% of bore)
- cc’d head (aiming for around 175psi of cranking compression)
- port match cases to cylinder
- JB weld and trench cases for high rpm flow (also shave cylinder skirts and piston ports for improved flow)
- Chinese copy 5mb reed cage for better flow angle and more intake area (this requires the cases to be milled 1.4mm each half/side for the cage to fit and cage mounting holes slotted to match case bolt holes)
- 5mm reed cage spacer
- Chinese carbon fibre reeds
- Chinese copy 5mb intake manifold
- Chinese copy 19mm Phbg Dellorto carb (however I may use a 21)
- stock derestricted airbox
- stock Ignition with stator plate slotted to advance timing (20-25* at 2k rpm depending on CHT’s and detonation)
- stock flywheel significantly lightened on my lathe.
- br9es plug
- trailtech tacho/CHT gauge
- Chinese expansion chamber (the specs of this pipe are slightly shorter and fatter but as close as you’ll get to the measurements I took from a mates S6 pro rep on his Aerox so it should match my port durations reasonably well.
- Chinese over range variator with a recut fixed half for better acceleration (I have 4, 5, 6 and 7g rollers to work with)
- Stock belt
- Stock torque driver with filed grooves for more travel
- Chinese 2k rpm contra (it’s the only one I’ve got laying around)
- lighted clutch with stock springs (My previous attempt at this was successful, engaging around 5.5k rpm
- Stock clutch bell

I don’t think I’ve forgotten anything there 🤔
All that said and done I’ve only spent $320AUD

[lokstar]

A few pics so far.
ill keep you updated and post more photos when I get around to the cylinder and head machining.

Filled and trenched cases, 5mb reed cage and cylinder spacer/ gaskets









lightened flywheel 547g (I forgot to weigh it before machining it down, I’ll probably take more off yet too.)
stator plate slotted and marked for 13, 20, 23 and 25 degrees.





lightened stock clutch. 625g total. Each arm is 147g. Stock was 172g each





and the build I did 2 years ago for my brother in law.
yes, that’s real lamborghini gallardo green!

[aeroxbud]

I like the thinking behind this build. Will be interesting to see what performance you can get before it goes bang!😯
I would of been tempted to see how far I could go with the 50cc cylinder first. Just out of curiosity.
Sometimes a bit more weight in the clutch can make it grip better.

Brother in laws bike looks great 👍

[lokstar]

Thanks man. I’ve thought about it long and hard and this is the best plan I can come up with for a budget build, knowing full well it will probably be short lived and go bang.
I was a little disappointed in myself for not refining my brother in laws engine build at all and now that it’s still going strong after a hard couple of years, I know there’s heaps of room for improvement.
I’ve been graced with another opportunity to build another one so I’m gunna make the most out of it this time. Even though I’m more or less trying to polish a turd 😂
I don’t particularly wanna wast time on a stock cylinder when I can get the 47mm for $70AUD

[oldgeek]

Great Job on the other scoot and GREAT plans and work on the current build! I like what you are doing with the reed and intake. It should make an incredible difference as it does in the 5bm motors. My only concern is with your cylinder selection. Depending on which one you end up with, I have seen some hideous china cylinders with transfer ports no amount of dremeling would fix. You clearly have the knowledge and tools to do things, this build is gonna rip so dont bottleneck it with a junk cylinder. Polini Contessa< (for the Dio not Minarelli Lol!) The Naraku sport is under $100USD is cheap and you can do your planned mods to it.

[lokstar]

Thanks oldgeek.
I’ve done quite a bit of research this time, ie the bell and Jennings books, the Thiel and Overmars threads and also read a lot of the threads on here too.
I liked the idea of 5bm cases and reed cage how it directs the flow towards the trans. This “should” be beneficial for high revs but not sure to what extent. I mean if China went to the extent of making castings, producing cases, and other supporting parts, there must be some weight to the theory. Plus I already had the 5bm reed cage so it was a no brainer to use it along with some jb weld to fill and flow the transfers. It’s only a hour or two worth of work.
I also like the idea of crank case area rather than crank case pressure(read the thiel and overmars threads) this unfortunately is not really a viable option with the 5bm reed cage as its bigger than stock so Im already loosing case volume with it and the slight filling/flowing of the transfers hence the 5mm reed cage spacer and slight trenching to regain a little volume. there’s just not really enough material in the cases to easily remove to much more without weakening them too much... I mean I could remove a few cubic cm here and there but Ide end up with glass cases and for how much gain 🤷‍♂️🤔
As for the naraku cylinder. I did look at them, but the China one was half the price and this is a budget build and the goal is to make the most out of the cheapest stuff I could find on eBay.
The China cylinder I used on the other bike was by no means perfect but it was not too bad considering. Hopefully I get lucky with this one too. Just gotta wait for it to arrive and find out what I’ve got to work with.

[Steve B]

Lokstar, Thank you for sharing you're build with us. I am eager to see this project move along, as i really feel it will be a budget build for the books.

[lokstar]

So my chinesium cylinder arrived today and let’s just say I’m glad I didn’t expect much, cuz that’s exactly what I got.
After a little patience and some finesse I tidied it up to what will be a useable cylinder.
It had mis matched port height, casting dags everywhere and wasn’t even honed 🙄
I port matched the cases to the cylinder and will do a mock assembly in a few days and accurately check the port timing with a degree wheel and decide on base spacer thickness.
Then I’ll be able to mill the deck height and set the squish and cc/compression with the head.
I had a quick play on the lathe and turned down a spare stock head to match the crown of the 47mm piston.
It’s 7.2cc with a 1.3mm recess from the deck. I imagine I’ll have to face it down to acquire the desired squish then compression will be through the roof and I’ll have to remove some more material in the combustion dome to make everything happy.

Before


After


Test cyl head/squish machining
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[190mech]

If you have enough meat,try a scaled RSA bowl;

[aeroxbud]

That was some ugly looking ports!😯

[Zino]

Impressive job salvaging what you picked up.
The quality control on these parts is non existent
The average guy would have just bought a paper weight .

I definetely will keep watching this build closeley

[Lucass2T]

Dude i got an eye rash from looking at that port map ugh!

[oldgeek]

WoW! You must have a 55 gal drum of turd polish! Nice work.

[190mech]

Hey!He wanted a cheap cylinder and thats what he got!!Wonder how many turd polish hours it took versus a quality,well cast cylinder?Soo nice to stare inside the transfer ducting in a quality jug and do some clean up,check the durations and squish and all is well...
Very nice work!! Carry on,keep us posted..

[Steve B]

Great work Lokstar!