I am going to make some WAGs (aka "wild guesses") about what has happened here. I was not there. I have not seen the engine and no photos were provided. So I'm completely working off my imagination and ~35 years as a certified motorcycle mechanic and engine builder. These ideas are offered here merely as help and should not be taken as a personal critique of the OP or his technical knowledge or ability. He has asked for help; I am merely offering insights. 

1. The oil pump is, of course, behind the flywheel. The only problem area I've ever heard of is the crankshaft thrust washers falling out due to the failure of the mechanic to "chock the crank" in a rearward position. Are you aware of this Airhead engine building necessity ? This may be a contributing factor.

2. I think the damage was done much earlier in the process than imagined. Most of the damage probably occurred during the test ride. Obviously the engine ending "loud click" happened while back in the shop, but I believe engine oil never really began to circulate. Modern engine oils being far better than we ever imagined and the Airhead running cooler than we ever imagined... thus making this feat possible. 

3. The pump also sits well above the fluid level of the oil in the sump. The suction needed to raise the oil into the pump is therefore dependent upon the pump's ability to create said suction. If I was installing a new pump, or doing any type of work on the old pump that required the cleaning the oil coating off the pump parts, then I would be re-installing ALL the pump pieces with a generous helping of grease. This because I know:

A. In an engine that's already got mileage, the parts in the pump cavity are already a looser fit. Fitting brand new oil pump rotor and impeller parts does not fully restore all the clearances to "factory" because some of the looseness will be in the surrounding aluminum engine block.

B. Input "suction" is the HARDEST thing to create in ANY pump; suction at the input is never a given. Just because a pump has tremendous output pressure is not proof that there will be any input suction. (A very common misconception.) This is why in dry sump engines (think Norton or Honda 750) the oil tank is always above the oil pump which allows gravity to assist in pump priming. And those pumps without this design feature (think manual well water pumps) almost always have a "prime hole", which enables the operator to manually inject liquid to assist the pump in startup.

C. Knowing the above, if I were building this engine I would have installed all the new pump parts with a gracious helping of grease to help seal the micro-gaps and improve pump priming and suction. Grease being nothing more than viscous oil that will stay in-place even if it's months before the engine gets cranked. And too, grease being a better lubricant than nothing, and one which is easily washed out and diluted when engine oil does finally arrive inside the pump. 

I don't know that these steps were or were not taken. Like I said at the beginning details are sketchy and these are only my thoughts... illuminated by a long history of dodgy oil pumps and stories of failed oil pump performances which I've witnessed.

Thanks for the reply......I did not pack the oil pump with grease on the original oil pump o ring. I just coated gears with oil.. I was not aware of oil light on during test drive or while adjusting timing but as my attention was on points and timing adjustment no oil pressure at that time is not out of the realm of possibility. The oil pressure switch is operable. When new gaskets and seals arrive I will reassemble.

How should I prime the oil system? The cold shop may be causing the drag on the rotation because of the thick assembly grease. Nervously will proceed with reassembly. Thanks again...any other thoughts will always be greatly appreciated.

Since it happened once already... I would take a VERY conservative approach.

>> It may turn out that you have an issue with your oil cooler or the thermal device inside the triangular oil filter cover that routes the engine oil. Not everyone lives in the moderate climate of north GA like me, but I remove the stock oil coolers and all their excessive plumbing as standard practice. I replace it with the simpler deep sump oil pan and the R75 triangular filter cover.

Steps you might consider before starting the bike:

1. You should be (generally) running 20W50 or 15W50 engine oil, unless you have a very good reason not to. This will be viscous enough at start-up to insure pump priming and adequate lubrication once running.

2. Remove the plugs from the cyl head and lay them (wired up) on the cyl head so that they are free to spark.

3. Remove the oil pressure switch.

4. Use the electric starter motor to turn the engine over. Continue to use the starter until you get at least a cup of oil from the pressure switch hole. 

5. Then hold your finger over that hole and use the electric starter again. There should be enough pressure to BLAST your finger off that hole at cranking speeds no matter how hard you press.

6. Use the empty hole to fit a pressure gauge to measure the oil pressure once the engine is running.

If you have low or no engine oil pressure...

* Replace the pressure relief valve (shuttle) and spring that's near the cam sprocket on the front of the engine. This controls the maximum oil pressure in the running engine.

* Replace the ball and spring of the oil filter bypass valve that's in the bottom of the oil filter well. These break all the time and allow oil to enter the engine without passing through the oil filter.

Here's where it hides...

Here's old spring and new spring...
?1

Hope this helps.

Hi George,  It was nice meeting you in Durham last week.  Your problem is quite intriguing.  I don't think you will unravel exactly what happen during the first assembly - but there are two things you said that I don't understand.  first "While assembling the engine tightening the oil pump cover caused the engine to tighten the rotation  of the crankshaft."  This would lead one to think the tolerance stack up in the pump cavity/pump rotor/cover was wrong or the inner to outer rotor gap. At dinner you said someone checked that for you. I would triple check that. Did you check the endplay of the cam after installing the gear?  The second is "Also when I tighten the timing gear cover the engine locks up. "  Again this implies a tolerance stack going negative - but for the life of me I don't see how installing the timing cover impacts the cam - so that says the tightening up is related to the crank.........  One test you could do is to remove the timing chain (separating the crank/cam relationship).  Then tighten the oil pump cover and feel if the cam binds up.  If it does - then you know its in the oip pump/cam free play stack.  If the cam is still free, install the fly wheel.  If the crank binds up then most likely the inner crank shim is off its pin.  If the crank and cam spin free then install the front timing cover and see if one or both bind up.  good luck and let me know - I will get your email from tex so we we can take this direct,

@wobbly thanks for the input  will very carefully assemble engine while turning over and monitoring oil pressure during all stages of assembly. Hopefully engine will loosen up as oil circulates. Will post results. thanks again ..any info is greatly appreciated.

One note on engine assembly. Learned you must heat timing chain cover and not force on during assembly.Also tighten bolts after cover is  flush.This has been noted on other post but thought I should repeat. Seems like air heads need a little finesse 

One further item in the same area but totally unrelated...

As of more than a decade ago, BMW released a stronger cam chain tensioning spring. If you are replacing the cam chain and/or CC tensioner blade, then the new, stronger spring should be installed at that time. You can no longer buy the older spring. The new spring is shown on the BMW Max parts diagrams, which is how I discovered this update. The new spring is a direct replacement and installs with no other changes.

Thanks