Engine finished but wont start

[Adammcf]

Finished rebuilding the engine and got the starter motor sorted.
On the second attempt it started and ran for about 20 seconds then I heard a light tapping noise so turned it straight off.
I adjusted the valve clearances as they had somehow got tighter than what I set them at a few months ago when I built the head.

Tried again and now it wont start. Its trying but not doing anything. I cant see the tapping doing any damage as it was very light and the engine was still running fine for the two seconds or so while it was doing it.

Maybe the battery pack just needs charged up over night to get a better spark going or something.

[Widge]

Have you checked that you are getting, a) spark b) compression c) fuel? These may seem obvious as you've just had it running otherwise I would say battery may need a boost.

[Adammcf]

Fuel is fine but have no way of checking the compression except that it feels ok when turning by hand when the spark plugs are in.
I havent checked spark yet but will be doing so tomorrow when Ive charged up the battery pack tonight.