[Supras] Whipping noise

[berniek at technicaldevelop.com]

Hmm..  The group has not seemed this dead in a long time.  Is the server 
down?


Anyway, my '91 (550cc, Lex, Walbro, upgraded IC, 3" exhaust) makes a 
very loud repetitive cracking sound from someplace near the front of the 
engine on cold startup.  It sounds almost like an amplified arc, or 
cracking of a whip when I listen under the hood.  Most times it occurs 
at random, but if I speed up the idle slightly, it occurs at times in 
sync with what appears to be every other revolution of the engine (i.e., 
4 stroke style).  The sound must be outside the engine, since it sounds 
like a cracking whip.  It appeared after about 600 miles on a refreshed 
JDM.  One thing I need to do is check the harmonic balancer bolt.  I did 
not tighten it all the way to the spec, as the pipe used on the breaker 
bar began to bend.  Could it be the balancer moving torsionally on the 
crankshaft against the woodruff key?  Strangely, once warmed up it is 
fine.  The stock pistons are fitted loose, and I do have cold piston 
slap as well, expected.  But this noise is far more "in your face" 
regarding high frequency content, not muffled or damped by the block walls.


BernieK