My vote is that the clatter is valvetrain noise. If you didn't lock down the adjuster nuts on the lash adjusters on the rocker arms, the lash adjustments could have opened way up. Recheck your valve lash. Make sure the piston is on the compression stroke so that you know the cam isn't trying to open a valve as you adjust the lash.
Use a feeler gauge, 0.002". As a sanity check, watch the valves open and close while slowly turning the motor over after you adjust. When you see that the valve has closed, just move the rocker arm by hand. The lash should just barely be perceptible. If you can noticeably "wiggle" the rocker arm (in the open and close direction) then the lash is most likely too big. Again, the last should just barely be perceptible. 0.002" is not a very large gap...
- Frank
1984 200ES Big Red
1985 350X (x2)
1986 350X
1986 250SX
1984 Auto-X
1984 ATC70
1985 ATC70