Well, so much for "bulletproof" straight 6, motors knocking :( - The 1947 - Present Chevrolet & GMC Truck Message Board Network

BIG CTY · 05-29-2007, 09:20 AM

I'm going to expect the worst, but hope for the best here. I was driving the balls off of my rust bucket awhile ago and when I came to a stop, I heard knock knock knock going along with the idle. When I speed up, the knocking gets quicker, when I slow down it gets slower. Its not nearly as loud at idle as it is when I get in gear and go. I was running a good 75-80 for about 15 mins, RPMS were between 3500 and 4k.

Now I know enough to be dangerous, but I'm not sure where to start here. I'm kinda hoping that its something simple, but anytime I hear knocking in the engine area I get scared. Anyone have any advice? The truck is for sale and there is no way I can sell it sounding like this. Where in the he!! do I begin tracking this down?

**Chevy Fleetside** · 05-29-2007, 10:11 AM

Get a piece of hose and while it is running put one end of the hose on the oil pan and the other over your ear.. If it is a rod knock you will hear it that way and you can determine where in the pan it is the strongest.. If you hear if from down there then you need to take the pan off and figure out which rod it is.. You will need to take the rod cap off and look at the crank. If the crank is not scored you can replace the bearing.. If it is scored then you will have to have the crank machined.. If you have a machanics stethescope (sp?) then you will not need the hose..

60-66 Nut · 05-29-2007, 02:08 PM

It's possible some carbon broke loose and stuck on top of a piston. Try mixing a little brake fluid and water in a cup, run the engine just above an idle and pour a little down the carburator, not enough to drown the engine but just make it run rough. If that doesn't help, then you may have more serious issues. Best of luck.

60-66 Nut

05-29-2007, 09:20 AM	#1
BIG CTY Between the earth and the sky Join Date: Oct 2006 Location: Chesapeake, VA Posts: 822	Well, so much for "bulletproof" straight 6, motors knocking :( I'm going to expect the worst, but hope for the best here. I was driving the balls off of my rust bucket awhile ago and when I came to a stop, I heard knock knock knock going along with the idle. When I speed up, the knocking gets quicker, when I slow down it gets slower. Its not nearly as loud at idle as it is when I get in gear and go. I was running a good 75-80 for about 15 mins, RPMS were between 3500 and 4k. Now I know enough to be dangerous, but I'm not sure where to start here. I'm kinda hoping that its something simple, but anytime I hear knocking in the engine area I get scared. Anyone have any advice? The truck is for sale and there is no way I can sell it sounding like this. Where in the he!! do I begin tracking this down? __________________ Chris - 1966 C10 Shortbed Fleetside, 1991 GMC Sierra 1500 Extended Cab, 1993 Blazer Sport 4x4 My other rides: 1969 Chevrolet Impala SS427 Convertible 1976 Dodge Tradesman B200 2002 Nissan Maxima 6 speed 2004 Mercedes Benz CL500 Last edited by BIG CTY; 05-29-2007 at 10:15 AM.

05-29-2007, 10:11 AM	#2
Chevy Fleetside Registered User Join Date: Sep 2006 Location: San Francisco Posts: 4,779	Re: Well, so much for "bulletproof" straight 6, motors knocking :( Get a piece of hose and while it is running put one end of the hose on the oil pan and the other over your ear.. If it is a rod knock you will hear it that way and you can determine where in the pan it is the strongest.. If you hear if from down there then you need to take the pan off and figure out which rod it is.. You will need to take the rod cap off and look at the crank. If the crank is not scored you can replace the bearing.. If it is scored then you will have to have the crank machined.. If you have a machanics stethescope (sp?) then you will not need the hose..

05-29-2007, 02:08 PM	#3
60-66 Nut Professional Beer Tester Join Date: Aug 2004 Location: Louisiana Posts: 453	Re: Well, so much for "bulletproof" straight 6, motors knocking :( It's possible some carbon broke loose and stuck on top of a piston. Try mixing a little brake fluid and water in a cup, run the engine just above an idle and pour a little down the carburator, not enough to drown the engine but just make it run rough. If that doesn't help, then you may have more serious issues. Best of luck. 60-66 Nut __________________ 60 Ford F100 Custom Cab 61 Apache Short Fleetside 64 C10 Short Stepside 65 C80 409 V8 5spd(X-Firetruck) 83 GMC 350 Olds Diesel 85 GMC Short Bed 86 GMC Short Bed 90 GMC R3500 Crew Cab 92 GMC 1500



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