[Supras] Noise at rear of oil pan: probably OK

[berniek at technicaldevelop.com]

Jon and list:


    Re:  Noise:  Modified '91 with freshened JDM, 550's Lex, 57 turbo, 
15 PSI boost, etc.:


    When I wrote the original post about noise at the rear of the oil 
pan last night, I was really concerned that something had gone awry, 
such as a nut loose on a connecting rod, or the extended oil pickup 
coming loose, or cracking off a piston skirt piece.  There are quite a 
few articles on the internet about skirts fatiguing and cracking off due 
to expansion control stress from the embedded steel strut in most 
passenger car engines (Stock Supra turbo and probably N/A pistons are 
this way to control noise.  The steel can be seen just below the wrist 
pin on both sides).  I remained with the stock pistons after everyone on 
the list stated they are fine at 15 PSI. 


    When I got home from work tonight, I took the car out and did 
repeated WOT acceleration runs back to back on I-80 to see if anything 
would come apart, or if the noise would get worse (take back roads to 
work, salted after the snow, a job for the expendable 54K mile 2001 
Maxima, which hopefully will last for a while).  Had the cell phone 
ready to call AAA for a flatbed if anything happened.  I gave the engine 
more of a beating then it deserved.  In one case, I shifted out of 
second gear a bit late, and saw 6500 RPM on the tach.  It is possible 
the previous owner installed an earlier ECU, which I did not check (I 
have changed engines since, the modified freshened JDM).  Post 89.5 
engines have a fully counterweighted crank, and will cut fuel at about 
6200 RPM (hit it more than once on my stock '90).  Also, idle speed goes 
up slightly when turning on headlights or any other significant 
electrical user.  Later ECUs, '90-up do not have the components 
installed to do this. 


    In any event, I pulled into the garage, jacked the front end up and 
listened again with the stethoscope.  If anything the random "pebble 
dropping" aspect of the noise disappeared.  My wife pulled in the clutch 
(Oh, not the the Gold Wing.  Miss in this weather) and there was no 
change in the noise, which now sounded like a galloping horse at the 
rear of the pan.  I'm becoming more convinced that I may have bent up 
the remnants of the oil pan baffle when cutting it away to fit the 
pickup relocated one main bearing distance to the rear.  The outer jaw 
depth on the pneumatic nibbler used to cut it away may have bent it 
upwards a bit.  Considerations are as follows:


1.  It is possible that the last connecting rod cap or bolts may just be 
touching it.  In any event, I'll be changing oil and filter again after 
the second 400 miles, and will cut the filter open again to look for 
metal shards.  I braked hard enough, just short of ABS actuation to move 
any sizable debris off the "shelf" at the rear of the pan into the sump. 


2.  I retained the filter paper remnants obtained from cutting apart the 
original filter (parted off the crimp bead in the lathe so no chips got 
inside).  With a high strength rare earth magnet, a surprising number of 
the metal shards were magnetic, found buy running the magnet under the 
"Bounty" filter paper, the filter pleats being washed off in paint 
thinner.  Most were long thin slivers, no doubt shaped by the oil pump 
gears.  Yet very little iron appeared in the oil. 


3.  Last night reported having heard a "cracking" sound when revving the 
engine once.  Tonight I could repeat it, and traced it to the front of 
the engine, either the PS pump, water pump, fan clutch, etc.  Once 
suggestion I received (Gracias) was to check the crank pulley bolt 
torque ( know it was not tightened to spec, but was maybe 250 lb-ft.  
I've heard cracking sounds like that in the past from warped or 
improperly tightened sheet metal pulleys. 


4.  I do know the valves (or journal caps again) on the intake side will 
need to be attended to, as clearances have increased slightly, probably 
due to loss of whatever soft coating was left on the journals after 
refinishing the caps for .002" clearance.  One or two intakes were at 
about .011", slightly over the stock limit of .009".  The exhausts 
checked OK when I had the covers off briefly last week, probably due to 
the coating being gone in the first place.


    As always, comments and other information to learn from would be 
appreciated.  I may have pulled the worry trigger too fast on this one.  
Hopefully so. 


       Bernie