Sounds like the wrist pin to me also. I have had some luck locating the bad pin by disconnecting plug wire one at a time until the sound stops. Not fool proof but it has worked for me in the past. Hope you find the problem before it turns into a bigger issue.
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11:57 AM
2farnorth Member
Posts: 3402 From: Leonard, Tx. USA Registered: Feb 2001
If you disconnect the plug wires one at a time do you find one that changes the knock? Useing a pipe or stick of wood as a stethiscope can you isolate the sound to a particlular spot on the block/head/bell housing? Check your dampner pulley to make sure it isn't coming apart and insure that your fly wheel/flex plate is not loose.
If the noise tends to go away of get better as it warms up, it may be piston slap. May have a bad lobe on the cam. Heard people say they've had a bad knock and it turns out the crank was broken in two. Only separated when it was removed (never seen this personally).
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06:33 PM
1fatcat Member
Posts: 1519 From: Zimmerman, Mn Registered: Dec 2010
Originally posted by Black Lotus: Heard people say they've had a bad knock and it turns out the crank was broken in two. Only separated when it was removed (never seen this personally).
I've seen it, on 2 stroke and 4 stroke engines.
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06:38 PM
PFF
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Dennis LaGrua Member
Posts: 15843 From: Hillsborough, NJ U.S.A. Registered: May 2000
Knocks can also come from a stretched timing chain. Get out the stethoscope and start probing.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
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06:53 PM
Spoon Member
Posts: 3762 From: Sadsburyville, PA. 19369 / USA Registered: May 2004
The big end of a rod could be egg shaped "width wise" if thats possible & the plasti-gage could of missed it depending on how good you were at using it. On the other hand were you alone when you heard the knock or were others around?
I remember playing a trick on a friend after he changed his oil. Upon startup I kneeled down by the front wheel "Non Fiero" and as he "goosed" the engine I'd tap on the fender to simulate an engine knock in direct proportion to his acceleration.
Just throwing that out there.
ps: I came clean before he brought in the cherry picker.
Spoon
------------------ Two yeast spent their entire life "about 2 days" discussing what the purpose of life could be and not once did they even come close to the fact that they were making champagne. Quoted by: Unknown
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06:58 PM
gtxbullet Member
Posts: 4180 From: Pewaukee, Wisconsin, USA Registered: Apr 2008
good thoughts from everyone. I've been helping billy over the phone for months now, and after finally getting another motor it seems as though goodluck has almost died off for him...
the person doing the work on the engine has been told a couple times to take the pistons/connecting rods out and inspect the wristpins. hopefully an issue will be found...I say this because if he says everything is fine inside the engine either gremlins are actually real or another mechanic is needed.
with good faith and optimism the issue will be fixed soon.
hang in there Billy, one way or another things will work out.
[This message has been edited by gtxbullet (edited 07-26-2011).]
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06:59 PM
Bill DeTucci Member
Posts: 138 From: Massachusetts -- Taxachusetts Registered: Nov 2008
The noise in the video link is also characteristic of what the loose pistons in some of the GM engines a few years back sounded like. As for the failed piston how are you able to determine for sure it was a wrist pin issue from the start and not a collapsing skirt that lead to the failure. The noise in the video sounded pretty much like my 3100 did with the clearance and eventual skirt problem.
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07:14 PM
Racing_Master Member
Posts: 1460 From: Hooksett, NH, USA Registered: Nov 2007
Id vote for piston slap. A lot of chryslers had this problem. Unfortunately the only solution for any of the thoughts presented here require pulling the motor and disassembly.
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12:07 PM
1fatcat Member
Posts: 1519 From: Zimmerman, Mn Registered: Dec 2010
Sounds like the wrist pin to me also. I have had some luck locating the bad pin by disconnecting plug wire one at a time until the sound stops. Not fool proof but it has worked for me in the past. Hope you find the problem before it turns into a bigger issue.
Thats -cylinder effiency test- good to try, and will also give a feel for how good the engiine is running whereas each diconnected wire should produce the same rpm drop. BTW: these are stock pistons and not forged, which have slap when cold.
If the noise tends to go away of get better as it warms up, it may be piston slap. May have a bad lobe on the cam. Heard people say they've had a bad knock and it turns out the crank was broken in two. Only separated when it was removed (never seen this personally).
The cam in my old Dodge was same way. Dont know how many years it had been broken.
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06:32 PM
Bill DeTucci Member
Posts: 138 From: Massachusetts -- Taxachusetts Registered: Nov 2008
I just got home, I was looking at the engine for him. its a bit of a mess, not running right now, missing bolts, etc. Some other people were working on it before and kind of left bolts on the ground. I took a look at visually inspecting the wrist pins, and checking for play in any direction at the crank and up at the wrist pin, and everything is tight. The pistons arent cracked, or loose in the bore, no evident metal wear or metal shavings in the engine oil. However the space between the Camshaft Timing Gear and the engine block seems way out of spec. its nearly touching, I couldnt get my fingernail in there.
So, knowing that there is a nylon thrust bushing in the back of the camshaft that prevents walking of the camshaft on the dukes, I suspect that the bushing is severely worn, or exploded (Nylon gets very brittle). It just doesn't seem right. We are arranging a way to get the car towed up closer to me, so I can get it in the shop I work at. Hopefully next weekend I can have this car running for him!
PS: There is a TSB on engine knocks caused by camshaft backlash, and I have seen it many times before on dukes (mainly in S10s). It makes one bad sounding knock, and a commonly overlooked item on the dukes! Once it's in my shop I will do a backlash check, to make sure its the camshaft that is out of spec, then its parts replacement time!
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11:57 PM
Jul 28th, 2011
Bill DeTucci Member
Posts: 138 From: Massachusetts -- Taxachusetts Registered: Nov 2008
Generally, piston slap goes away after the engine warms up and the piston expands from heat.
In very mild cases. My experience was reduced noise at first but before long it made little to no difference. As the clearance increases so does the noise audible inside and outside of the car.
For piston measurements note that they are barrel shaped and will be larger in diameter at mid girth than at the top or bottom.
[This message has been edited by Joseph Upson (edited 07-28-2011).]
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11:55 AM
1fatcat Member
Posts: 1519 From: Zimmerman, Mn Registered: Dec 2010
Actually, they are tapered. Larger at the bottom than the top. The bottom of the skirt is always the largest diameter. And yes, you're right about the piston slap. Eventually, it doesn't go away.
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03:07 PM
FriendGregory Member
Posts: 4833 From: Palo Alto, CA, USA Registered: Jan 2004
Originally posted by 1fatcat: Actually, they are tapered. Larger at the bottom than the top. The bottom of the skirt is always the largest diameter. And yes, you're right about the piston slap. Eventually, it doesn't go away.
There have been some changes as indicated in the diagram in the link. I had read about it but also measured the barrel shape characteristic in my pistons old and new. The bottom of the skirt was not the widest point in my measurements. I guess it depends on the manufacturer and the measurement point. My stock and forged pistons where both made by Mahle.
Sounded to me like a loose rocker, like when I was adjusting the ones on my SBF while idling.
Rockers are all 100% tight on this engine, perfect amount of play. Rules that out. I am 90% positive its the camshaft at this point. as soon as we can get the car closer to me, I'll be able to final diagnose it to make 100% sure its the camshaft backlash making the noise.
the TSB related to the noise:
quote
Number 86-6(Gasoline)-64 Date 10/86 Subject: ENGINE TIMING GEAR NOISE (KNOCK)
1985-86 6000, FIREBIRD, GRAND AM, AND FIERO MODELS WITH 2.5L L4 ENGINES IF AN ENGINE HAS A KNOCK AND THE PRELIMINARY DIAGNOSIS IS A "CAM GEAR KNOCK", USE THE NORMAL PROCEDURE DESCRIBED IN BULLETIN 85-6(Gasoline)-39 TO CHECK CAM SHAFT END CLEARANCE AND GEAR BACKLASH.
MEASURE THE BACKLASH AT POSITIONS OUTSIDE THE TWO RETAINER PLATE ACCESS HOLES AND AT TWO OTHER AREAS 90 DEGREES FROM THESE HOLES.
NOTE: CRANK PULLEY MUST BE INSTALLED AND TORQUED BEFORE MAKING BACK LASH MEASUREMENTS. IF END CLEARANCE IS NOT BEYOND .0015" (.0038 CM) TO .0050" (.0127 CM) AND BACKLASH IS NOT BEYOND .0005" (.0013 CM) TO .0095" (.0241 CM) AND THE CAM AND CRANK GEARS ARE NOT DAMAGED, THE GEARS ARE NOT CAUSING THE KNOCK. EXAMINE THE ENGINE FOR OTHER SOURCES OF KNOCK.
IF END CLEARANCE IS LESS THAN .0015", REPLACE THE SPACER RING; IF IT EXCEEDS .0050", MAKE CERTAIN THE GEAR IS SEATED PROPERLY AGAINST THE SPACER AND IF IT STILL EXCEEDS .0050", REPLACE THE THRUST PLATE.
IF BACKLASH IS LESS THAN .0005", OR GREATER THAN .0095", REPLACE THE CAM AND CRANK GEARS.
RECORD THE END CLEARANCE AND BACKLASH READINGS ON A TAG AND ATTACH IT TO THE REPLACED PARTS. REVISED TIME ALLOWANCES FOR DIAGNOSIS, R AND R AND/OR REPLACEMENT OF CAMSHAFT TIMING GEAR OR CAMSHAFT ARE AS FOLLOWS: OPERATION VEHICLE SERIES NUMBER A F N P GEAR, CAMSHAFT - REPLACE J0840 7.3 6.2 9.3 9.1 CAMSHAFT - REPLACE J0850 ADD: WITH A/C .3 .4 .6 .9 WITH CRUISE CONTROL .2 .2 .1 REPLACE CRANK GEAR .2 .2 .2 .2
EDITED TO ADD:
Since this info doesnt seem to be here, yes, it is a 2.5L Iron Duke engine :P
[This message has been edited by Racing_Master (edited 07-28-2011).]
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05:15 PM
Bill DeTucci Member
Posts: 138 From: Massachusetts -- Taxachusetts Registered: Nov 2008
ever thought it could be something external to the engine like the water pump. my 2.5 s10 the water pump bearing was soo loose it sounded like a rod knock. but it didnt leak a drop of coolant. also how much slack is in the timing gears? do they look worn out. im assuming that you have checked the piston to cylinder wall clearance automatic or stickshift? couldnt be a broken clutch spring could it? gremlins dont exist so... there is a legitimate reason for what is going on. it could also have been a misfire or pre-ignition mistaken for a knock. just more things to check from an extra pair of eyes
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10:45 PM
Racing_Master Member
Posts: 1460 From: Hooksett, NH, USA Registered: Nov 2007
ever thought it could be something external to the engine like the water pump. my 2.5 s10 the water pump bearing was soo loose it sounded like a rod knock. but it didnt leak a drop of coolant. also how much slack is in the timing gears? do they look worn out. im assuming that you have checked the piston to cylinder wall clearance automatic or stickshift? couldnt be a broken clutch spring could it? gremlins dont exist so... there is a legitimate reason for what is going on. it could also have been a misfire or pre-ignition mistaken for a knock. just more things to check from an extra pair of eyes
Automatic, I checked for slack, it doesnt seem to be gear slack in the timing set, the cam gear appears to have walked twords the block, the thrust bushing doesnt appear to be there anymore. I have to check its actual clearance first, though, with a feeler gauge, to be sure.
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10:48 PM
BlackGT Codde Member
Posts: 1107 From: Gallup, New Mexico Registered: Mar 2008
i don't know if this is recommended but i was thinking if you could rotate the engine forward to take out slack then turn it back you should find the slowest reacting piece. evidence of the knock. and yes the cam would be a great place to start. speaking of which. where would i find one of those thrust bushings. my s10 has a steel one and it shattered.
[This message has been edited by BlackGT Codde (edited 07-28-2011).]
oil pressure/volume ? Perhaps there's not enough oil for the parts to ride on. You might not have any observable damage YET. a failing oil pump or blocked passage will absolutely cause knock even on perfectly clearanced parts.
well if you want a 2.8 and wiring harness you can have the one i pulled for free it has a standard tranns flywheel i think i have ecu's for both standard and automatic
