I've got an A15 in my Bugeye Sprite and I just rebuilt the head (valve grind & resurfacing). I have reassembled everything and adjusted the valves, but when the engine warms up it chatters. I have tightened up the clearances a bit, but it still makes noise when it is hot (runs quiet when cold). Any ideas?

The specs say .35mm hot.....I have them at .28mm hot. I'm afraid to go any lower.....how much tighter can I safely go? What else could it be? It didn't make this noise before and the only thing I did was get a valve job.

I'm at my wits end!

Check the wiki on the left side of the page.
I believe there is some info about clearance in. I would post it up for ya but don't have my book righ now.

<-- wiki clicky

If you adjust to the spec, and the valves are still noisy, then your only solution is to replace the worn/bad parts. If you tighten the lash up you run the risk of burning a valve.

When adjusting, be sure there is a light drag on the feeler gauge. If it is just a bit loose, it will make tapping sounds.