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I think this might be a big problem. On my way to work my 80 4x4 started making a knocking noise when I accelerated. The noise is gone when coasting even at high rpm's. The noise sounds like bad gas or low octane fuel knock but it has fresh gas. I pulled the valve cover and everything looks fine no dropped valves, broken rockers, or strange looking things in there. At idle it sounds like there is a cylinder that is not firing. I pulled the plug wires one by one and I think it is the 3rd or 4th cylinder. Both are getting spark. Thought it might be a spun bearing but I don't know what that sounds like and I still have oil pressure. Thanks for any help

is it coming from the top or lower?

how loud is it ?


I had a knocking noise in my luv just like that.
started after 7000rpms.
one year later .
I got a rebeild kit and stated to work.
got the head off it was OK.
pistons from the top looked OK
the rods look in the block looked OK
on bolted the rods from the crankshaft.
out of 4 pistons 2 had craked skirts. the rest had broken skirts.

the way that thay broke thay stead in with the pistons.

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4.3l V6. 5 speed MT 2.55 in the back.

OK i have narrowed it down to the # 3 cylinder. When I pull the 3rd plug wire off the engine hardley looses any rpm's and when I rev it with the wire off the noise is gone when I plug it in the knocking sound is back. Is the best way to figure out what is wrong is to pull the engine and take it apart??? I hade another idea. Could it be a sticking valve in the open position? I thought this would cause the cylinder to be out and the rocker to be hitting the top of the valve instead of staying in contact. the problem is that the noise is only there on acceleration and when it reaches a certain rpm it goes away. I would think that the noise would be constant with a sticking valve. I want to look and see what the valves are doing when the engine is running but with the valve cover off it is like taking a shower in oil. Is there any way to stop the shower. Any suggestions will help. Sorry for the long post.

It sounds like what you've got is a rod knock, and yes , you are pretty much looking at a re-build, although sometimes if the damage isn't too bad you can get away with just a crank kit. If you have to pull the engine to get the crank out, you might as well go all through it.

What and where is a good kit to get. I have looked on napa and there are many kits to choose from... complete kit for over $400, bottom kit for $130-170 depending on regular or performance rings. My problem is that that the engine sounds like it has lost a cylinder. Does this happen when a rod nock occurs??? I still have oil pressure and I thought that if the rod bearing was shot the engine would loose oil pressure. I can't determine where the sound is comming from. I have been under the truck with a helper reving the engine and I can't tell where it is coming from. I don't want to spend time and money on a rebuild kit if it is something else. Thanks for the replies.

ive had this problem on a holden gemini, as you accelerate there is a knock coming from the block, its what they call piston slack its quite common with these lil 4 cylinders. yeah it requires a re-build ya have to get the block honed as well.

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