Causes of tight wrist pins and scuffed pistons ?
12-08-2012, 05:53 PM
#1
Causes of tight wrist pins and scuffed pistons ?
Engines were HAWK 525's
35 hrs all using 93 octane pump gas
5100 max rpm, never held there for more than 60 seconds at a time mostly cruised at 3900 rpm
454's .030 over (going to measure exact bore tomorrow)
TRW 2399 pistons
088 heads 119cc chambers
28* timing ngk r5674-7 plugs
had b&m 174 blowers with 800 cfm holley's
comp 280 ah 114 cams .547 lift 280/288 114 lsa
rod and main bearings look fine, couple marks/ lines but not beaten out or uneven wear
7 out of 8 pistons in each engine had tight wrist pins, a couple galled the piston when pressed apart.
3 scuffed pistons in one motor, 2 in the other.
Machine shop says detonation but the plugs look perfect, no signs on the domes of the pistons and the upper bearing halves are mint.
I believe they were assembled at .004 piston to wall but will measure to verify, and are going back together @.0065
Any ideas what caused this ? was it detonation ?
I don't run thermostats in the intakes water temp is usually around 135-140 and I never run it hard right away always idle for 5 minutes or so away from the ramp.
They have hp500 oil coolers and thr=ermostatic oil filter heads.
Any help or input is greatly appreciated.
35 hrs all using 93 octane pump gas
5100 max rpm, never held there for more than 60 seconds at a time mostly cruised at 3900 rpm
454's .030 over (going to measure exact bore tomorrow)
TRW 2399 pistons
088 heads 119cc chambers
28* timing ngk r5674-7 plugs
had b&m 174 blowers with 800 cfm holley's
comp 280 ah 114 cams .547 lift 280/288 114 lsa
rod and main bearings look fine, couple marks/ lines but not beaten out or uneven wear
7 out of 8 pistons in each engine had tight wrist pins, a couple galled the piston when pressed apart.
3 scuffed pistons in one motor, 2 in the other.
Machine shop says detonation but the plugs look perfect, no signs on the domes of the pistons and the upper bearing halves are mint.
I believe they were assembled at .004 piston to wall but will measure to verify, and are going back together @.0065
Any ideas what caused this ? was it detonation ?
I don't run thermostats in the intakes water temp is usually around 135-140 and I never run it hard right away always idle for 5 minutes or so away from the ramp.
They have hp500 oil coolers and thr=ermostatic oil filter heads.
Any help or input is greatly appreciated.
Last edited by Unlimited jd; 12-08-2012 at 05:55 PM.
12-08-2012, 06:18 PM
#3
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im thinking detonation because the wrist pins are tight,the piston pin bores are probibally egg shaped/out of round .i believe the pistons are forged,and .004 piston to wall is a little to tight,espically on a blown deal,but the plug in the pic looks good.what is the compression ratio,and how much boost at wot?also,who did the assembly.
12-08-2012, 06:24 PM
#4
8.8-8.9:1 compression ratio standard fel pro marine head gaskets 5 lbs wot, 140* water temps, I bought the motors out of my buddies boat with less than 10 hours on them. He had all the receipts etc. Have to check who did the assembly.
8.84 according to jeg's
8.84 according to jeg's
Last edited by Unlimited jd; 12-08-2012 at 06:27 PM.
12-08-2012, 07:34 PM
#9
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Tight wrist pins would cause the skirt to skuff, piston could not rock freely and would cause side load on them. If you had deonation to the point of knocking a wrist pin hole out of round the upper rod bearing would show copper. Post pics of the rod bearings. sound like poor machine work, and bad assymbly. Side clearance sounds a little tight for a boosted motor, but the piston manufactuer would have the determaining specs for their product.
12-08-2012, 07:35 PM
#10
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James...did you check the ring gaps? That's the only thing you haven't covered....you looked at every thing else. I have seen this before...the motor I saw that was like this was set up too tight on the clearances ( Rod and Main Bearing along with ring gap) and what I remember looked like your pics.
