Engine knock please help

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Model T Ford Forum: Forum 2012: Engine knock please help
Top of pagePrevious messageNext messageBottom of page Link to this message  By joshua jasysyn on Saturday, September 08, 2012 - 06:06 pm:

when i took my 26 t for a ride the other day i noticed when i get the engine speed up to about 20mph it gets a very deep and very loud tone, but at idle it is fine, this happens both while i am driving and in neutral. i lifted up the hood and noticed that the sparkplug for the cylinder closest to the back of the engine had vibrated loose i shut off the car and tightened up all plugs and wires fired it back up and the noise was still there.

i suspected it to be a main bearing and found there to be a very light tint of green in the oil and the oil also seems to be a bit watery or lighter than from when i changed it 3 months ago.

i also suspected it could be carbon deposits causing the knock because of the loose sparkplug so i took out all the plugs and noticed the top of the back piston being saturated with oil and what looked to be spots of carbon deposits. in all of the other cylinders the pistons have a dry black soot.

so after finding all these problems i am unsure which is the cause of the loud deep knock if not all please help


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Saturday, September 08, 2012 - 10:18 pm:

You noted a light tint of green in the oil. Do you use green antifreeze in our coolant? If so, you could have a coolant leak into #4 cylinder. Knocks can be caused by many things. If you short the spark plug wire to the head do you notice a difference in the sound? A connecting rod knock is usually loudest when going about 20 MPH with the engine loafing. Just a little gas at that speed. If you back off completely or advance the throttle the knock will lessen. A piston slap will usually be loudest with a cold engine and quiet down as it warms up. A main bearing knock will be loudest when pulling. Carbon knock will be a tinny Ping noticed most loud when the engine is hot and pulling hard. The knock could be unrelated to the loose spark plug. Check all cylinders by grounding the spark plug wire to the block. Use an insulated screw driver while the engine is running at the speed where the knock is most pronounced. It will either get louder as you short the plug or it will disappear. Let us know what you find.
Norm


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