[Supras] Whipping sound

[berniek at technicaldevelop.com]

Jeff:


    The whipping or cracking sound appears more and more to be a 
sticking bucket or valve.  It happens occasionally when cold, although 
one in a while it occurs for several cycles in a row, just one valve 
from what I can tell.  Once, and once only, did I catch a misfire as it 
happens, which appears to clinch the sticky valve or bucket hypothesis. 


    It happens only during warmup, and occurs at its worst when the 
ambient temperature is low.  I did some bucket swapping as part of the 
valve lash setup, but all seemed OK at the time from a fit standpoint, 
on the bench.  Further, its just now beginning to appear at about 750 
miles, although the warmer weather when I first got much of the first 
mileage on it may interfere with that observation. 


    At 18 PSI boost, I'm wondering if the soot formed during rich 
combustion is finding its way up the exhaust valve stem, since the 
exhaust pressure could perhaps open the garter spring loaded valve stem 
seals.  The sound happens infrequently enough that without day after day 
listening (also with a stethoscope) it is impossible to tell which 
cylinder or intake/exhaust side it it coming from although it is near 
the front.  Yesterday I thought I had it pinned down to the intake side, 
but now I' not sure.  I'm starting up the car each day now (can't use it 
most days due to rain, salt not yet gone from the roads, and some light 
snow) and listening more. 


    The greatest fear is in throwing a shim.  Have you had it happen?  
Any and all ideas and commentary would be appreciated.  Thanks.


    Bernie