How to check the crank big end for ware ? , It feels tight and no play , also the side movement of the Con rod is just over 1 mm , I will replace the small end . is there any other way to make sure all is ok before I rebore cylinder and rebuild the motor , thanks 

The best way to check for wear in the bigend is to just grab it and see if there is any movement up and down in the bigend bearing. They all move side to side a bit. Yours sounds as if it is fine. If in doubt replace it but it sounds okay. Graham

I just have them re balanced if there's no up and down play another way to check is rock the bottom to see if the big end as any worn bearings. 

If the motor has been sitting for years without the big end covered in oil then it would be a good idea to replace the conrod while it is apart. It's fairly common for a big end that has been sitting for a long time to show no movement or play but fail quite soon after going back into service, due to corrosion of the rollers or the surface of the pin. You can always have a look through the oil slot in the big end for any tell-tale marks (lines of discolouration running across the pin where the rollers run) on the big end pin. The bloke who rebuilds my cranks prefers to push them apart to have a better look but you might not have that luxury.

The usual failure mode for two-stroke trials bike big ends is running the engine after a long static storage rather than due to hours of use.

If you know it has been run regularly over the years then there probably isn't corrosion in the big end. I've got a few 1970s trials bikes that still have good big ends and have done lots of trials and trail riding work, because the oil in them has never had the chance to dry out.

Thanks all for your advice, I have decided to replace the big end , better safe than sorry , Haybob