70cc to 50cc Conversion

Hi All
Anyone point me in the right direction here? I know it seems a bit backward but, I have an ST70 (6v) and wish to put a 50cc barrel and piston etc on it so my wife can ride it on her car licence. Are all the 50cc barrels the same (bore diameter and stroke length (other than if they've been rebored) and can I put my 70cc head on the 50cc barrel?? I picked up a 50cc barrel and piston/rings off ebay for a tenner and I have already have the 70cc bits (head/valves/cam/cogs etc).

Let me know guys - I could do with some help on this as I dont want to bugger it up!!!

Thanx!!

The 50cc will fit right on the 41.4mm Honda stroker.
The bore is 39mm compared to 47mm for the 70cc.

The main thing you've got be carefull for is that you buy a piston for 6v!!!
The distance between pen and top is different from the 6v and 12v crank.

The opther bad news is that there are no 50cc pistons for a 70cc head.
So it won't fit.
You'll have to swap the head for a 50cc version.

Or, get a 47mm bore with 49ccm written on it. (witrh a 6v 47mm piston for 70cc head)
Still illegal, but if you limit the bikes speed, unlikely to be noticed.

DAX-IT!!! wrote:Hi All
Anyone point me in the right direction here? I know it seems a bit backward but, I have an ST70 (6v) and wish to put a 50cc barrel and piston etc on it so my wife can ride it on her car licence. Are all the 50cc barrels the same (bore diameter and stroke length (other than if they've been rebored) and can I put my 70cc head on the 50cc barrel?? I picked up a 50cc barrel and piston/rings off ebay for a tenner and I have already have the 70cc bits (head/valves/cam/cogs etc).

Let me know guys - I could do with some help on this as I dont want to bugger it up!!!

Thanx!!

Hi seems an odd thing to do! i would have put another ST/C50cc engine in it and stored the original. But if u r after a good 50cc head i might have a barrel too!! incl rockers cam n valves ive got one up for grabs. It wil save alot of problems.
Ade