knock on startup then immediately goes away?

HELP please! Have a mid 70s Ford 302 has a knock as soon as you start it then goes away within 2-3 seconds? Just did an oil change and see nothing in oil. Engine runs smooth, only does this after it has set overnight.

 

lifter

 

Yep, most likely a lifter bleeding down when it sets.

 

I was thinking main bearing but then that wouldnt make sense since it goes away rt? whats the fix? The engine was a runner when pulled and sat for a while, thinking maybe it just need to be run a bit?

 

New lifter equals fix.

 

To me a lifter is more of a tick, not a knock.
My wifes OT Ford with a 302 and almost 300,000 miles on it will knock on startup for a few seconds after sitting overnight, which I attribute to a rod bearing. Just my .02

 

I would say Main Brg,,,, You said it knocks,, a lifter would click tick or tap.

 

Main bearing,a jug of hyper lube every oil change, it will last YEARS! I got another 150k out of a 300 six the same way.

 

I agree.
knock = rod bearing
tick = lifter

 

Did you add any oil to the filter before you installed it or put it in dry? I had that happen then started putting maybe half a quart in the filter before installing and no more knock. See if that works.

 

yes it was about half full before installing the filter, it was doing this before the oil change and is what prompted the oil change, oil had maybe 100 miles on it, running good filter no fram ****!

 

main (fords are known for it) bill

 

I'd try a pint or so of MMO in the crankcase for a few hundred miles before trying anything more involved.

Jack E/NJ

 

Then it's most likely a main bearing. If you take it easy it will last a while but prepare for an overhaul.

 

I agree if it's more of a loud Ticking or Tapping noise, it's probably just a sticky lifter and it may go away with driving - maybe add a little marvel Mystery Oil or Rislone or similar to the oil to help free it up

If its truly a Knock, then it probably a bearing and only a rebuild will fix it.

 

I think you could run a 300 six without oil and you couldn't kill it! Same with a slant 6 those things are indestructible!

 

I had a knock in a SBC in my Nomad that would go away quickly after the engine started. It was a wrist pin.

I had a knock in my flathead that could only be heard when I first started engine and when I got above 30 mph. I thought main bearings. Turned out to be rod bearings de-laminating.

Guessing won't fix it. You're gonna have to isolated location of noise if possible and ultimately tear into the engine.

 

Hard to isolate it as it only does it for a second after sitting overnight, not much time to listen around?!

 

I have a 6 liter chev that does that and it is piston slap-------thats what the dealer says

 

Try a different brand of oil filter. There are also at least 2 numbers that fit that motor.
Long and short filter and a mopar number that is inbetween. Different companies and different numbers have a valve in them that keeps the oil up there others drain down.
Was a big problem with all car manufacturers in the 80's. They built them loose for gas mileage.. oil would drain down and you had that early morning rattle.

 

Just went from napa gold to a purolator still doing it?!!!!

 

Sounds like a lifter.

 

Yup,heard that brief knock on start up on many Fords, especially 351's. Doesn't seem to hurt anything.
Of course check the lifters to be sure.
Or do nothing until it gets worse.

 

My first question was gonna be is a sbf, I thought they all did that.

 

If by chance it had been built a bit[forged pistons] in it's past the answer could be piston slap on cold startup,they'll do just that knock a second or three then no more noise all day on starting= till completely cold startup.....
a lot of newer centerbolt 350 chevys were replaced for the noise in late model trucks......
try idling it down as -slow- as it will idle and see if you can hear it then,that would confirm ordinary piston slap from wear......

 

I had a bunch of high mile small Ford motors do that and will last forever,if the knock does not go away you have problems but nothing to worry about if it does. I always try to fill the filter before installing it and I use a Motorcraft filter instead of the cheaper ones.

 

I second what junkyardjeffsaid......use motorcraft filter. Does it do it on a hot restart after say...fifteen or y minutes? I have used a dowel about two feet long placed against my ear( be careful!) have someone start the car and try to zero in on the noise by placing dowel one end on intake manifold etc, it may take a little moving around to find the right source of the noise, obviously if it's a main it will be centrally located, if it's a lifter you may be able to pick out the noise coming distinctly from one side...good luck!

 

GM's excuse for to much clearance, lol. Them things all do that, but its more of a tick type noise rather than a deep knocking sound.

 

We have an interesting mix of opinions here. I would make this guess.
1. con rod brg
2. lifters (the sound here does not die out as immediately as con rods after oil pressure is achieved). Lifters on a 300, I might add, can be very oil-level sensitive. Mine tell me when it is time to add a quart, very faithfully! You might even try overfilling your crankcase a little (I will bet you right here it will help, providing it is for sure lifters). A new set of lifters sure can make an old 300 sound sweet and quiet, too.

 

If it truly is a rod or main bearing on it's way out, you should be able to hear that same noise after warm up if it's under load because the oil is thinner when warmed up. To diagnose it easier, eliminate road noise and just put it in gear and run the RPM up with the brakes applied. Doing this between two building will help you hear it better. I've got a '68 wagon that has the cold start up noise then quiets down at idle - however the noise returns while accelerating from a light or ascending a grade(climbing a hill). I know it's terminal, but haven't got "a round to it" yet. I hope it's just a lifter in your case, but it seems more like "piston slap" to me. Forged pistons? Lots of newer cars do and start up noise is very common with those.