piston

Hi all I am trying to help a lady who has got a 1976 honda St 70 dax , it has had a new cylinder head and piston fitted by someone else due to the piston being holed due to a valve snapping , Since the new piston and head have been fitted the bike is running slow and has lost all of its power , I have check3d the valve timing and it is set up right but on further inspection the cam chain adjuster is very slack , Now I have all so noticed that when I have mesured across the barrel the piston is at TDC it is 1.5mm below the level of the barrel in the center , Now my question is should a new cam chain and roller kit been fitted . Is there another piston for this bike (its a 6v model ) or could any one tell me what else to check
.

Are you sure you did use a 6v piston?
The 12v piston is 3mm lower.
This due to the different length of the 6v-12v crankshaft.

Waynus wrote:Are you sure you did use a 6v piston?
The 12v piston is 3mm lower.
This due to the different length of the 6v-12v crankshaft.

Waynus
someone else fitted the piston but I think you are right , I messured from the middle of the piston that came out at 1.5mm but I also messured from the outside and this was 3mm so it looks like you are right , So I will pass all this back to her I have also dicied to change all the cam timing gear at the same time , many thanks for the infomatiom

You're welcome!
You can also spot the difference by looking at the piston top.
For OT cylinder heads (6v - OT50 or OT70) there is a dome on the piston.
While the 12v versions are almost flat, with only very shallow dents for the valves.

Waynus thanks for the pictures , yes its a12v piston thats been fitted now where could I get a 6v piston from any ideas
Geoff

Where are you located?
CMSNL has them (banner on top of the page), and pretty much every web- and local shop. (Monkeybike.co.uk has closed some time ago, or at least their website)

This is what you need:
47mm piston, 6v for OT70 head.

Waynus , I live in north east England a place
called stockton on tees about 48k south of Newcastle , I phoned csml today and I will need the engine number but at the moment I am in scotland on a course so I will check it all out on saturday onec again thanks for all your help I will tell you how I get on with it


Geoff

Their part number 13101087712 + ring set 13010087003 + maybe you'll need to replace the clip (better safe than sorry!) 13115001000.
But yes, telling them you engine number is a great idea to ensure the correct order.