Rebuild

82 should be correct.
Did you make sure the chain runs OVER the big black plastic roller which is mounted 'inside' the cylinder?
Have you got a manual or auto chain tensioner?
Are you sure the timing is correct (T mark)
All cylinder studs correctly tensioned, all bushes in place?
Take off the flywheel and stator place and look at the tensioner and cam wheels.

It should be fairly tight, yes.

mdclsc wrote:Hi All
Well I have finished rebuilding a St70 Dax 6V ,It had a 12v piston fitted by someone after the old one had hit the valve and wrecked the head a new head has been fitted (E22) with the letters SUNK engraved on one of the fins.The bore was ok no marks and was a Std size, I fitted the 6v piston and rings along with new gaskets and seals but when I started it up its burning oil ( very light blue ) a black oil residue is coming out if the exhaust breather that is above the engine filler cap , Has anyone got any ideas what the problem could be .

Right guys
First of all I would like to thank everyone for the input in to the thread I have learnt a lot , I have now found the problem I was checking the cam adjuster and that looked ok so I diced to fit the new cam chain and carry out some checks I removed the head and barrel along with the piston rings just to double check the ring gaps and on inspection these were ok , I then started to refit the rings and snapped the oil ring so I thought that was my day over !!! No it had just started just out the corner of my eye I noticed a mark I on the head on further inspection to the head and piston the marks matched , Yes the piston had been hitting the head and just touching the valves I did a leakage check on the valves and phew both are ok after making a phone call to shire bikes it was confirmed that a 50cc head had been fitted and due to the combustion chamber being smaller and a 6v piston fitted this was why the piston was hitting the head , I also have found out why it was burning light blue smoke the exhaust valve guide seal is u/s . So the question is do I get the head machined as well as the piston (that will be new) or does a kind Dax ST70 owner have a spare head for sale or a C70 head ,

http://www.ebay.co.uk/itm/Honda-C70-Cyl ... 43c40942df
I suggest to get a cheap one, and save the money for a rebuild.
That way, you'll be 100% sure everything is in good condition.
A very good OT70 head will set you back +100£