OK a few little updates. Hi Mitch, keen eyes there! I scraped away a little bit of black stuff on the head and came up with this...
[Linked Image from farm6.staticflickr.com]

Then I cleaned up the dirt from around the exhaust and came up with a hole which is I am guessing is the one you were referring to.
[Linked Image from farm4.staticflickr.com]

So it looks like a worthwhile motor to fix up.

Now the reason that I think that it is a conrod big end bearing is due to the amount of movement I can get it to do, and not in the proper direction frown .

This is where it should be

[Linked Image from farm3.staticflickr.com]

But if I jiggle it a little, I can get it to move like this

[Linked Image from farm4.staticflickr.com]


This bearing needs replacing

[Linked Image from farm4.staticflickr.com]

I need to find a bearing puller now and get the crank apart, I am guessing the bits of metal which came out of the crankcase are mangled bits of rollers.

B