C90Club.co.uk

Hello, after reading a lot of very helpfull previous posts on here about big bore kits vs new engines, I think a Lifan 110 looks a safe bet, the 125 seems to throw in some additional work.
I got my 1972 Honda CT70HK1 6v 4 speed manual clutch with the plan of doing a couple of long distance trial this year The engine seems healthy apart from an oil leak through either the gear change shaft or sprocket shaft seal and petrol dribble from carb overflow (parts at the ready to repair). My thinking is I should get a bit more low to mid grunt out of the 110, the 70 engine will be stored under my bed and refitted when I do the bike up like a tarts handbag next winter.
Has anyone done an swap to this model? I will appreciate any advice or guidance, I realise I will need to change the electricals to 12 v, but not sure whether the carb and exhaust will need to be changed/altered. Thanks.

Use a cheap pit bike exhaust, and CDI loom.

It’s just nuts and bolts really.

Hi. And welcome to the forum.

This is my 76 ST70 the UK CT70.
This is fitted with at the time a 12V C90 engine taken out to 98cc(50mm bore) with a 4 speed CT70 gearbox and clutch,loom is made from a c90 one.
Engine is now 102cc but has been 121cc for a bit.



Any questions just ask away.

steve g

Thanks for the kind welcome chaps and the pictures of 2 magnificent steeds.
Diesel Dave, that looks like a good tool for a bit trail riding, have you done any events trial or enduro on it?
SteveSt100 I thought that was a nitrous canister on the side. The configuration and variations on these bikes and engines is boggling.
I had a couple of sleepless nights getting my electrics sorted even with the correct USA diagram, till I discovered the ignition key had a second position
I had considered using a C90 crank and big bore kit but can't figure out if I would need a C90 6v crank due to the points (on mine located behind the Hitachi magneto flywheel) do any of you know if this is the case or would a 12v do?

Canister on the side is a catch tank for the engine breathers and drains back in to the extra bit i had welded on top of the clutch cover.
The 6v c90 is a no no for use as they are the odd ball one(with the CT90/110 ATC90/110/125)and wont fit.
Are you in the uk or us as that would make engine choice for a big build on what engines you can use.

steve g

I'm in Newcastle UK and have noticed the US have an advantage parts wise. Thanks for the advice on the crank, think I'll take the Lifan option, but out of curiosity do you know if aC90 12v crank would fit the cases and support the Hitachi flywheel to operate the points, is the morse taper the same?
Nice job on the breather by the way with the finishing touch of a K+N style filter at the end.

The 12v c90 crank will fit the cases but the 6v and 12v have different tapers on the end so will not fit the 6v flywheel.
12v top.


You can get around this by using the crank from a early Jincheng m50 which is a 12v cdi crank but with the 6v taper on it,and for a c90 size crank you need the one from the DX90/110.Good luck finding one as they are very sought after by the monkeybike and SS50 owners.

steve g

Ta very much for the photo and sharing your wealth of knowledge. Things are more complex than they look in the C50, 70, 90 world.
Lifan it is then, but 1st speedo drive gear to fit and re-seal the leaky engine before storing.