Cold knock

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Dec 11, 2020 | 01:12 AM

F-250 restorer

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From: Near Los Angeles

Cold knock

Hey guys. I have a 300 with about 7,000 miles on a rebuilt engine. Just recently when I start it in the morning, and it runs rough because I'm still dialing in the choke of a new carb, I've been hearing a knock. Press the clutch and the knock disappears. As the engine warms up and the initial rough idle diminishes, the knock goes away. It lasts for about a minute. All day long there is no knock. Does that sound like a rod knock? Any ideas?

Dec 11, 2020 | 02:15 AM

SonofaFord

Mountain Pass

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I would think a rod knock would be heard all day long at idle. If you're pressing in the clutch and it goes away, I would be looking at the clutch and back in the transmission.

Dec 11, 2020 | 05:39 AM

Tedster9

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Joined: Apr 2002

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From: Waterloo, Iowa

Sounds a little like "piston slap".

Cold engine: odd knocks and various strange unidentifiable noises - Sometimes OK.

Warmed up engine: odd knocks and various strange noises - Always Not OK.

Dec 11, 2020 | 11:18 AM

440 sixpack

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Pushing the clutch in and making it stop can only mean one thing if you're sure the noise is actually coming from the engine. it would mean you are pushing the crank up tight against the thrust bearing flange. which in itself shouldn't cause any noise, but if it moved a rod bearing or wrist pin enough to make a difference then maybe.

I'd sooner think a clutch or transmission noise but hard to say.

Dec 11, 2020 | 11:23 AM

78Fords

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From: Everton MO

Throwout bearing?

Dec 11, 2020 | 12:20 PM

symonds86

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From: upstate ny

You stated in another post you get trans noise at low rpm so you raised it 100 rpm and it went away I'm guessing while it's running ruff either the rpm is a little lower causing the same trans noise, or the ruffness itself is causing the same trans noise. Pushing the clutch disconnects the engine and trans so no noise then when it's warm the idle and smooth running is back to where you set it to eliminate the noise.

Dec 11, 2020 | 12:33 PM

F-250 restorer

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From: Near Los Angeles

Quote:

Originally Posted by symonds86

Hey there. Thanks for the reply. I have a zf5 trans that is freshly rebuilt. At idle, in neutral, idling at 750 rpm, it growls, a faint diesel running sound. Since the diesel growl gets worse if the engine is running rough, and the zf5 if famous for transmitting engine noise, I thought that with my large cam the engine would run smoother, and therefore quiet the diesel growl. So I raised the idle to 800 rpm and now the growl is quieter.

The knock mentioned in this post could possibly be related. I'm still tracking that down. Thanks.