Rebuilt 350 TBI knock at low idle

[dhumboldt12]

Noticed a dull knock after driving around and getting it to a low idle. Only happens in drive, where the idle it low enough, any gas, and the sound goes away. Motor was rebuilt about 45k ago, with an M55HV pump, holds about 45-50 psi cold, and 30 or so fully warm. Ideas?

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[DerekTheGreat]

Not all rebuilds are equal. Sounds like the bottom end could be "loose". I once had a '69 Plymouth with a rebuilt 318 that would knock when started up fast. I ran 20w-50 in it and began cranking for 20 seconds before the ole throttle pump and no more knock on start-up. Other things could cause that noise though..

 

[dhumboldt12]

Not all rebuilds are equal. Sounds like the bottom end could be "loose". I once had a '69 Plymouth with a rebuilt 318 that would knock when started up fast. I ran 20w-50 in it and began cranking for 20 seconds before the ole throttle pump and no more knock on start-up. Other things could cause that noise though..

What's your suggestion?

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[Oldblue98]

Noticed a dull knock after driving around and getting it to a low idle. Only happens in drive, where the idle it low enough, any gas, and the sound goes away. Motor was rebuilt about 45k ago, with an M55HV pump, holds about 45-50 psi cold, and 30 or so fully warm. Ideas?

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They are known for a piston slap noise, but that is usually on cold start up idle. There is many write up's on that subject.

 

[90halfton]

Warranty on it still by any chance?

 

[dhumboldt12]

Warranty on it still by any chance?

No. Done by a local guy a few years back.

 

[dhumboldt12]

They are known for a piston slap noise, but that is usually on cold start up idle. There is many write up's on that subject.

Got that as well.

 

[dhumboldt12]

I pulled the inspection cover off before, and the starter was hitting the flexplate, but i've since resolved that.

 

[dhumboldt12]

Worthy of stepping back up to 10-30? currently running 5-30 valvoline, wix filter, 1 qt of lucas

 

[DerekTheGreat]

I personally don't like Lucas Mucus. The SAE studies I've seen show them to be junk. I run 5w-40 in my truck, Valvoline SynPower (Full synthetic, they've now changed the name) with Purolator Boss Filters. 4,000 miles with the "new" motor (144k miles now) and it used ~1/2 quart. That oil change saw me run a can of Restore in it. This oil change I didn't add any of that, we'll see if it's necessary. Truck seems to like the 40 wt. I'm no engine builder so my remedies tend to be habit changes or off the shelf. Try a can of Restore & see what happens.