Quiet Knocking at start

[xirdneh]

I just installed a salvaged engine and when i started the car the engine was making a quiet knock for about 20 seconds that i attributed to oil builing up pressure in an engine that had not ran for two years. But it does it every time when the engine is cold and lasts about 20 seconds. The only time I have ever had this happen in any of the Tercels I have worked on was during 25 degree or less weather. The weather has been 35-40 degrees lately. I'm not too worried about it but do wonder what it might be?

[rer233]

probably piston slap- not unusual for an engine with miles on it. once the aluminum pistons expand a little bit from combustion heat, the knock subsides. i've got a boat with a built 454 chevy engine that has forged pistons that raises HELL till it runs for a while. i would'nt be concerned as long as the oil pressure light goes out as soon as the engine is running. (how many miles on the "new" engine?)

[Petros]

Also could be worn out bearings, too much clearance until the oil pressure builds enough to take up the slack. DId you check the bearings when the engine was out of the car? It is easy to drop the pan when the engine is out. OTOH, it would not take 20 seconds to bring the oil pressure up, more like 5 to 10 sec. Piston slap is a likely sourse of noise, but that is more of a hollow rattle than a knock.

I had a car with piston slap, it only had about 180k miles on it. It made a harmonic rattling sound as certain rpms, eventually it caused the piston skirt to fail. I had to rebuild it and bore it out, even new std. pistons could not get the clearance within acceptable limits.

I also once had a valve guide come loose so it was moving up and down with the valve, you could hardly hear anything was wrong, I had eventually burned a chunk of head off the valve and had to pull it and discovered the problem. You can inspect for that by looking at the valve guides through the springs.

A worn rocker arm could also cause a mild knocking, until it warms up. see if you can tell if it going with the crank speed, or with the valve train (half the crank speed). Pull each spark plug in turn, start it and see if it combustion related. Use a mechanic's stethoscope and see if you can isolate it. A long screw driver pressed against your ear, and the other end pressing against various parts of the engine works pretty good.

You might just have to live with it until it becomes more obvious, and hopefully you will not cause worse damage later.

Good luck.

[takza]

The fuel pump can make some noise until it loosens up...see if you can locate it to being near the pump?

[xirdneh]

mileage on the engine was over 200,000 but i do not remember how far
fuel pump is new
does not sound like the tapping from valve related stuff
i was thinking about recording it
my recorder creates mp3 files
how would i go about posting that?

[dlb]

post the audio clip on youtube and put the link on here. that's probably easiest.

[xirdneh]

after almost a week of starting the car and recording the "in the morning cold engine" knock
it stopped knocking on the fourth day
i have not driven the car during this time
just idling it for a while in the mornings while recording the sounds
when i get to a better net connection i will post the recordings
hopefully the knock will not come back