What is this knock?
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Senior User
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From: Powhatan, Virginia
What is this knock?
Puhleeze offer some insight on this "new" knock.
Just recently when old blackie has been sitting for a day or two, it knocks for a second or two on startup then quits and sounds/runs fine. A mechanic friend of mine said it is a rod bearing slapping a bit until the oil pressure builds up. He advised that if this is all its doing.....run it.
Anybody else had this happen before?
Just recently when old blackie has been sitting for a day or two, it knocks for a second or two on startup then quits and sounds/runs fine. A mechanic friend of mine said it is a rod bearing slapping a bit until the oil pressure builds up. He advised that if this is all its doing.....run it.
Anybody else had this happen before?
Postmaster
Joined: Jul 2003
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From: Pittsburgh
It's incredibly common on 300-6's, but it's not a rod bearing slapping. It's a lifter pumping up. It doesn't necessarily hurt the motor, but if you don't like hearing it go and buy an actual Motorcraft oil filter for your truck. When you get it, look down in there and make sure there's a little (typically red) disc in there.
This disc is an anti-drainback valve, it keeps oil up in the motor overnight to prevent dry starts.
Justin
This disc is an anti-drainback valve, it keeps oil up in the motor overnight to prevent dry starts.
Justin
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Postmaster
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From: Pittsburgh
Well, is it a really fast knock (as in the speed of the crank) or a slower knock (about 1/2 the speed of the crank)?
If it's a fast knock is it a high pitched knock or more of a low pitched knack knack knack? If it's really fast it could be at the crank, but most knocks at the crank show up at other times besides startup. Like light rod knocks (high pitched knock) tend to show up on deceleration while main knocks (low pitched knack, sounds like it's coming from deep deep inside the motor) tend to show up under load.
BUT, the fact that it's on startup after it has set a day or so suggests that it's a lifter that has bled down completely. A really dry one can make a knock, but it's a knock that verges on sounding like a tick and is also typically accompanied by a tick.
IMO, for the $3.50 a motorcraft oil filter costs and the $1.50 a quart of oil costs, it's a cheap way to figure out if all it is is a bled down lifter or something you should actually be worrying about.
Justin
If it's a fast knock is it a high pitched knock or more of a low pitched knack knack knack? If it's really fast it could be at the crank, but most knocks at the crank show up at other times besides startup. Like light rod knocks (high pitched knock) tend to show up on deceleration while main knocks (low pitched knack, sounds like it's coming from deep deep inside the motor) tend to show up under load.
BUT, the fact that it's on startup after it has set a day or so suggests that it's a lifter that has bled down completely. A really dry one can make a knock, but it's a knock that verges on sounding like a tick and is also typically accompanied by a tick.
IMO, for the $3.50 a motorcraft oil filter costs and the $1.50 a quart of oil costs, it's a cheap way to figure out if all it is is a bled down lifter or something you should actually be worrying about.
Justin
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Depends on how loud it is. It's probably a rod bearing, like your friend says, but if it is not real loud, let it go until it is. When you can tell is if you change your oil, or let the truck sit for several days, and then when you start it up it sounds like someone hitting the oil pan with a hammer before it quiets down, THEN it is time to get new rod and main bearings.
