Engine has a knock at idle

[Michael_B767_ATP]

Hi,

Trying to track down a steady knock in the motor, it goes away a touch above idle and it doesn't happen all the time. 1970 440 with A/C. Anyone know of any trustworthy mechanics in the Boca Raton area of Florida?.

Thanks
Mike

[73440]

I used Automotive And Air Specialist 106 Commerce Way Bldg A-1 Jupiter Fla 33458 561-747-7007 M.V.#13598 multilple times for repairs on my daily driver van, a little further than Boca but you could call and see if he can help you.
I moved from Fla 6 years ago so would call first.

[Cuda Cody]

What compression and fuel grade do you run?  Have you tried running same race fuel to see if the knock is detonation related?

[Michael_B767_ATP]

Hi Cuda,

The compression I do not know, as for the fuel I added five gallons of C12 to a tank of REC 90.

Thanks
Mike

[73_Cuda_4_Me]

I would also verify what the timing is at idle... if there is a large cam installed, might be a little too much advance at idle... easy to check by backing it off a hair to see if knock goes away...

[cudabob496]

header hitting frame

[jimynick]

Couple of things- what's the oil pressure at idle? Does it knock on acceleration or deceleration of engine speed? Does it knock at the float point between those two and is it a sharp or lower register knock? Does it only do it at start up or even when the engine is up to temp? 

[YellowThumper]

Couple of things- what's the oil pressure at idle? Does it knock on acceleration or deceleration of engine speed? Does it knock at the float point between those two and is it a sharp or lower register knock? Does it only do it at start up or even when the engine is up to temp? 

All valid questions to be answered.
Knock at idle was an issue for me many years ago. Spum bearing. Oil pressure still registered well because with spin the oil hole blocked off. Lower idle knocked because there is limited load to rpm. Parts could flop and bang. Increased rpm sound would disappear.
Of course hope this is not your case. But sounds familiar...

[Michael_B767_ATP]

Hi,

Looks like I'll have to end this to someone, now to find someone.

Thanks Everyone
Mike

[Bullitt-]

Do I recall some folks describing a knock from a worn down fuel pump rod?

[ScottSmith_Harms]

It could also be related to your AC compressor.

[headejm]

I like to use an automotive stethoscope to identify where the knock is coming from. Fairly inexpensive tool and very useful. 

[gumby]

I like to use an automotive stethoscope to identify where the knock is coming from. Fairly inexpensive tool and very useful. 

You can also use a long screwdriver placed against your ear. Place the screwdriver where the sound is coming from, and place your ear next to it. ON your ear.

You will be amazed at what you can hear.