engine KNOCK
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engine KNOCK
Hi there, new to the board and I am scratching my head over this one.
I have a 1983 ford box van, it has a 460 in it. It runs like a champ, does not smoke or burn any oil but when you run it for a bit (15 minutes or so) it develops a loud knock. It is a solid type knock, some where near the top side. I can't pinpoint it though. Checked all the rocker arms and replaced a worn one.
Now here is the tricky part. Sometimes it doesn't knock at all. I'd say around 15% of the time it does not knock at all, and about 85% of the time I get the knock after the motor warms up. Any suggestions??
Thanks
Dave
I have a 1983 ford box van, it has a 460 in it. It runs like a champ, does not smoke or burn any oil but when you run it for a bit (15 minutes or so) it develops a loud knock. It is a solid type knock, some where near the top side. I can't pinpoint it though. Checked all the rocker arms and replaced a worn one.
Now here is the tricky part. Sometimes it doesn't knock at all. I'd say around 15% of the time it does not knock at all, and about 85% of the time I get the knock after the motor warms up. Any suggestions??
Thanks
Dave
Post Fiend
Joined: Oct 2003
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From: New Jersey
Originally Posted by fordboxtruck
Now here is the tricky part. Sometimes it doesn't knock at all. I'd say around 15% of the time it does not knock at all, and about 85% of the time I get the knock after the motor warms up. Any suggestions??
when oil is cold, its thicker, more like syrup. Once it warms up, its much thinner, MUCH thinner.
So somewhere you have a marginal bearing, and the crank, rod, cam, something, when the oil thins as it warms, is banging metal on metal.
Its possible that it might be piston slap, meaning one of the bores isn't round anymore, but slap occurs regardless of temperature. A dry/wet compression test will tell you if any of the cylinders are leaking.
If you want to pinpoint the noise, take a soft flexible tube (like a fuel line hose) and put one end to your ear, and the other end onto the engine in various places. When the knock gets louder, thats approximately where the problem is.
Elder User
Joined: Sep 2003
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"Its possible that it might be piston slap, meaning one of the bores isn't round anymore, but slap occurs regardless of temperature."
Incorrect. Piston slap occurs only with a cold engine. As the engine warms up, the aluminum piston grows faster that the cast iron block and the slap disappears.
If the piston is loose enough to slap with a warm engine, then parts of the skirt will be in the oil pan before very long.
Incorrect. Piston slap occurs only with a cold engine. As the engine warms up, the aluminum piston grows faster that the cast iron block and the slap disappears.
If the piston is loose enough to slap with a warm engine, then parts of the skirt will be in the oil pan before very long.
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