first start on rebuilt engine

[s13-t]

So I rebuilt my SR last year then ran out of funds. I eventually got it back in the car and during the last few weeks got it ready for its first start.

Turned it on today. Basically the engine ran smooth for a few minutes. then started making a loud tapping sound. I listened to the sound for maybe 10 seconds before turning it off

At idle before the noise...
oil pressure was good
aem uego said 13.5
voltage good
vacuum was at like 18
ran smooth especially for the home made engine mounts

noise description
sounded like a tapping, metal on metal. definitely not a knock or lifter tick
the sound was rhythmic with the rpm
the sound seemed to come from the front of the engine, cyl 1 or from in the front cover.
the sound seemed to be coming from up high in the head but not the valvetrain.

I think that the noise has something to do with the timing chain or tensioner or guides.

basically What does NICO think the problem is? what all should I check before starting it again?

[Lobo240sx]

Chain is hitting guide. I believe 2 12mm bolts it should come off. Sounds should disappear.

Or chain is loose causing the same problem.

[s13-t]

Yea thats what I was thinking.

I also talked to sean at kiezen speed. He basically said the same thing. He said that I should remove the valve cover, check the tension of the chain, the chain tensioner, and if all checks out then remove the top guide and see if the sound goes away.

I will try that on monday and post the results.

[s13-t]

Removed the chain guide, sound went away.
but now there is a new problem.
I watched the a/f ration slowly lean out. When i first started it the gauge read 14.5 but after idling for a few minuets it was up in the 17's
I figured that It must just run really lean at idle so i gave it a lil throttle to get it to 2k and the ratio was still in the high16's low 17s.

let me know your thoughts

edit:
did some searching and now have a list of things to check.
but I am fairly sure that I am getting bad numbers due to an exhaust leak before the sensor. My cheapo ebay downpipe is warped on the elbow flange. its always caused an exhaust leak and its probably the problem.

edit:
all is well. seems to run fine now