Crankshaft/connecting rod play. - Team Camaro Tech
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post #1 of 10 (permalink) Old Mar 24th, 03, 08:57 AM Thread Starter
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This noise on my crank is driving me nuts! 327 SBC seems to knock from the crank just above idle - not a spark knock/ping. It's not the damper, or the flex plate. I got the pan off, no spun bearings, nothing! There is a small amount of radial play on a couple of the connecting rods on the crank journals - the rods do not move left and right in relation to the crank, but there is a small amount of play - back and forth. How much tolerance in radial/back and forth play is allowed in a SBC? Should I buy some feeler gauges? What should I look for with the pan off?
What does a bad wrist pin look like?
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post #2 of 10 (permalink) Old Mar 24th, 03, 10:43 AM
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This spec. is called connecting rod side clearance and should be about .009"-.016" between the rod pair as measured with a feeler gauge. This really shouldn't cause a knock even if the engine measured over .025" per pair!!

I would check again for main and rod bearing problems, flex plate, piston slap (excess piston to bore clearance), cracked piston pin bore etc...

good luck!
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post #3 of 10 (permalink) Old Mar 24th, 03, 03:05 PM
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Yah I'm thinking that's the sound a little bit before throwing a rod. Hope not. Gotta eat.
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post #4 of 10 (permalink) Old Mar 26th, 03, 02:45 AM
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I agree with PDQUICK, the clearance tolerances are between .009"-.016", but I have seen as much as .030" without any issues. The machinist who did the work on my engine block claims that the oil will compensate for this difference and shouldn't pose any issues. Are you using forged pistons in your engine? They tend to give the old 'piston slap' noise at idle until the engine comes up to the appropriate operating temperature. Hope this helps.
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post #5 of 10 (permalink) Old Mar 28th, 03, 12:44 PM
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Ok - this is going to sound way to basic and easy - but it's worth a shot.
I recently ran into a 350 that had a 'funny' little knock that came and went just above idle. It was the Timing Chain hitting the cover - go fiqure. Had run into this before but it always sounded like a lifter not a knock.
Worth looking at anyway.
I would otherwise agree with the check all the bearing clearances and then the pins as others replied.
You may be able to spot bad rod pin if it has turned color from lack of oil - will be blueish color. They usually only go bad from original defect or lack of oil (plugged oil hole) unless this is a really high mile motor.
Keep us posted on what you find.

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post #6 of 10 (permalink) Old Mar 29th, 03, 02:47 PM
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Pry on the crank front to rear to check for crank end play. Iv'e seen the thrust bearing wear out and the front of the crank weight hit the block. The knock was worse when the car was pointed downhill, and went away uphill.
I think clearance is around .006" but check a book to be sure.
David

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post #7 of 10 (permalink) Old Apr 1st, 03, 07:25 AM Thread Starter
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Davidpozzi,
Could a thrust bearing wear out within ninety miles? The engine has good oil pressure...
Ryan
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post #8 of 10 (permalink) Old Apr 2nd, 03, 02:30 PM
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It could if it wasn't "set" before final-torquing the rear main cap; not everyone knows you're supposed to do this, and if not done, it can eat a thrust surface in a hurry. [img]graemlins/thumbsup.gif[/img]

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post #9 of 10 (permalink) Old Apr 3rd, 03, 09:34 AM
 
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Try using some plastigauge and check the clearence. on the extreme get your crank turned .10 that should fixed it. [img]smile.gif[/img]
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post #10 of 10 (permalink) Old Apr 4th, 03, 08:02 PM
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Anything can happen. Just pry the crank forward and rearward and see if there is excess movement. It should barely move.
David

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