Knock at Idle

[Ian Curtis]

I have a pronounced knock at idle, which goes away when you advance the spark. (Not sure if the sound is going away, or just being drowned out by the engine noise) It also goes away if you short out the #4 plug with throttle/spark at idle and retarded.. What do I need to do next to diagnose/fix the problem?

Video of knock (beginning is retarded, after I go in the cab is advanced)

Thanks!

[Mitch//pa]

sounds like an exhaust leak to me

[Big hammer]

X-2 what Mitch said

[jax55]

X-3 what Mitch said. Exhaust manifold gasket or bad connection pipe to manifold .

[Tom Wesenberg]

X3 what Mitch said.

I'd get rid of that rubber fuel line and use a steel line from the dealers. You could then stick one end of the rubber hose in your ear and hold the other end near the exhaust clamp to see if that's the noise.

[Ian Curtis]

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Sweet! That sounds like a much cheap problem. I will investigate tomorrow. I had a screwdriver to my ear all over the block and could never find a source... that might be why.

[Chuck Sea/Tac]

I like to use the cheap harbor freight stethoscope withe metal end removed and replaced with a rubber hose.

[WestCoast]

if it is a knock and it goes away when you short out a plug, my guess would be a rod knock

[colin1928]

hard tell on the video but sound like gudgeon pin

[Mitch//pa]

if it is an exhaust leak it sounds loud enough that it should be fairly easy to locate without any listening devices..
usually engine knocks sound worse when advancing the spark

[James Rogers]

Exhaust leak on #4 port. Get that fixed and try again. Hard to hear any kind of knock over that noise. If you are mistaking the leak for a knock, that is why it goes away when you short #4.

[Ian Curtis]

It's pretty clear that this manifold has not been off the car for a looooong time (Mr. PB is hard at work). What is the recommended sealant to go with the gasket, since I assume #4 has drooped?

[Tom Wesenberg]

Copper Coat should work, but I usually just use the copper exhaust gasket dry. If you have enough sag by #4 to cause the leak, then it's best to buy a new ex. manifold. The repros are excellent.