china bike 122cc dohc 4 valve project

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tormentandglory

tormentandglory

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Hi everyone :) Just thought I'd tell people about my mini project I've been working on. I'm building a twin cam china bike engine.
The japanese kits are badly overpriced, I'm tired of burning cash on kitaco and takegawa engine parts. I've built a lot of mini engines in the past 10 years or so and I thought I'd have a go at building a china bike that was a bit more special.
I've started with a mojo 110cc three valve engine. It now has a gpz400 piston which makes it 122cc. I'm using zxr250 valves, cams and all associated hardware. For the actual head, I'm using the original 3 valve thing, but i've cut the back off it, welded the ports and chamber up totally, and re-machined my own chamber and ports. The camshafts and buckets will be supported in a billet alloy cambox, which bolts to the back of the head (unlike the takegawa one-piece design).
I've uploaded a few pics of the progress so far. Its been slow going, and there's so much work to do! Getting access to the machines at work is tough sometimes as well. I'm hoping it will be running in a few months.
I'll post updates as I get further into the build.
 
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There is an obscene amount of work in it and I'm not even a 1/3 of the way there yet. And I don't know if its gonna work, I have no drawings. I'm just working out of my head.
 
SWEEET...keep up the good work !! Anxious to see how its running....what size does have the valves?? what cam do you use??Will it be for dirt or street??
 
it'll be for dirt. i'm using the zxr250 cams, the valves are 19.5 and 16.5mm. I'm putting it in an xr50 :)
 
thats some crazy stuff, do you mind if i ask why you have put in the extra couple of holes in the chamber? the ones between the two sides if that makes any sense, sorry i am lost for a better explanation.
 
tubes380 said:
thats some crazy stuff, do you mind if i ask why you have put in the extra couple of holes in the chamber? the ones between the two sides if that makes any sense, sorry i am lost for a better explanation.
Click to expand...

Not quite sure what u mean tubes, but the hole in the middle will be the spark plug hole, and theres a bit of a blemish next to it where the welding isn't quite perfect.
 
Amazing

Wow, I can't wait to see how you make the timing chain operate the 2 cams.
Good luck. Ride on MSO
 
tormentandglory said:
Not quite sure what u mean tubes, but the hole in the middle will be the spark plug hole, and theres a bit of a blemish next to it where the welding isn't quite perfect.
Click to expand...

He's talking about the two reliefs at the ends of what appears to be a flame trough .... You've done a stack of work there mate ...... it's good to see someone having a go at engineering their own parts ...... :cool:

You're spot on about the Jap parts being grossly over priced for what they are ....... and you're obviously a skilled tradesman who's fully in the know so you can see it whereas a lot of others can't .....
 
tormentandglory said:
it'll be for dirt. i'm using the zxr250 cams, the valves are 19.5 and 16.5mm. I'm putting it in an xr50 :)
Click to expand...

wow...isn´t there any issue with the clearence to the front wheel...that head looks huge...or will you cut it down a bit??:cool:
 
thanks cactus thats what i meant, why have these??? wouldnt it be better without as itll up the comp. and its not a smooth journey for the flame around those tight radius'
 
Cactus Jack said:
He's talking about the two reliefs at the ends of what appears to be a flame trough .... You've done a stack of work there mate ...... it's good to see someone having a go at engineering their own parts ...... :cool:

You're spot on about the Jap parts being grossly over priced for what they are ....... and you're obviously a skilled tradesman who's fully in the know so you can see it whereas a lot of others can't .....
Click to expand...

Ah, ok, I see what you mean. The chamber has only been rough machined. I'll finish it by hand with a die grinder when I get closer to completion. I'm aiming for 10.5:1 or 11:1 comp.
The cambox will be much smaller when its finished, I have to rip a hell of a lot of metal off it yet. I made sure I bought a block of alloy that was much bigger than I really needed. It sux when you get 1/2 way through something then realise that you don't have enough material to do what you need to.
 
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And regarding the jap parts, they are a lot better, but not good enough to justify the price. If you've ever seen the takegawa super R heads with the titanium valves and billet alloy roller rockers you'd see how much better the jap stuff can be.
I'm an auto machinist by trade, I built racing engines for 10 years but I've been working as a cnc toolmaker/fitter and turner for the past 5 years. Its a good mix of skills, and I have access to an awesome workshop.
 
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AWESOME...I would love to do that too...would build my bike completely ...with looooots of strange, bling parts hehehehe
 
man you have some great skills and its good to see them going to good use :)

thats one hell of a great project and sounds like its got some good internals, im sure that it will run it will just be how well and not dout itll go off with flying colours ohh and its going in a xr so youll be right :p

good luck man, keeps us updated :)
 
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