Quick Knock right at engine start up..

[Dunamis]

Sometimes when I start up my 1500, I hear a quick knock. It knocks like four times and then goes away. Any input?

[termite88]

Originally Posted by Dunamis

Sometimes when I start up my 1500, I hear a quick knock. It knocks like four times and then goes away. Any input?

i have had a few trucks that do this and have always thought that it was the lifters tapping because the oil had leaked down. i am far from being a mechanic but thats my thought. hope it helps

[Dunamis]

What does that mean and is it something I can fix without replacing the engine?

[J-Ri]

The lifters in most engines (including yours) are hydraulic, they expand to take up slack in the valvetrain. When the engine is shut off, there is no hydraulic pressure to keep them "pumped up". There is a check valve in them, and if it goes bad, they can leak down, and the noise you hear is the slack in the valvetrain. Lifters can be replaced without removing the engine.

It is very hard to diagnose a sound over the internet (without a recording), but lifter noise would usually be described as tapping, not knocking.

[Dunamis]

I have heard a car "tap" when the oil is way overdue for an oil change. It sounds like a tapping and it get's faster as you press the gas. In my situation, my car knocks four times and goes away. To me the "noise" sounds a bit like knocking on a door or counter top with your knuckles.

How do I figure out if it is in fact the lifter? Furthermore, how do I gigure out which one it is?

[jveik]

does it go away right as the oil pressure comes up? that would explain your lifter problem. my truck will "tick" very quietly after about 2000-2500 miles on the same oil, so i replace it every 2500 miles. i wouldnt worry about it too much unless you have bad oil pressure

[Dunamis]

I jump in the truck and turn it over to crank it. As soon as the truck fires up it knocks/taps no more than four times, then goes away. As far as my oil pressure is concerned, upon start up the oil pressure reads a little under 50 ro 60 (3/4 on the guage) and then after it warms up then needle is right at the about 40 (@90 degrees).

I think this is about average, right?

[jveik]

yeah that is about the same as my truck, i have a 95 k1500 with a 4.3 v6 (4.3 is basically a 350 that is missing 2 cylinders). sometimes the pressure will go above 70 in the winter when the motor is still cold and i have it at any more than idle rpm, but other than that it is like yours, 60 when off idle, and 40 when idling fully warmed up. mine sometimes does a faint tap until the oil pressure comes up upon starting, this period of time is maybe one second, perhaps less, as the pressure comes up pretty damn quick. if you are really worried, have a mechanic look at it when you first fire it up, but on these higher mileage trucks (mine has 182k miles) a few wierd noises are not worth worrying about. my truck has been doing that occasional faint clicking on startup since i bought it with 150k miles, so 32k hasnt seen it get any worse...

by the way, would you compare the noise to the noise that it makes when you first fire it up after changing the oil, mine clicks and clacks until the new oil fills up the filter and makes its way to the top end. the occasional knock i get sounds similiar to this

[Dunamis]

Yea I would say that statement is accurate. I'm a nervous person by nature. I just want to be sure everythinhg is operating correctly under the hood so that I can get the outside where I want it.

[Dunamis]

Here's the latest, I took my truck to a mechanic concerning this "knock". I explained to him that it sounded like a lifter to me. I started up the truck to see if it would actually knock for him and did. He got this puzzled look on his face. He said that it didn't sound like a lifter to him. He said it sounded like frint/rear main bearings or possibly the crank shaft, but he could tellwhich end it came from. What puzzled him is that it only "knocked" four times and then went away. After that, everything sounded perfect. Absolutely NO ENGINE NOISE WHAT SO EVER. He commented that the truck ran remarkably well. He said he was a member of "all data" web site or something and he would look to see if some report was issued describing this issue.

Hopeflly he comes back with good news. He also so that the only way for me to really see what made the noise was to dig into the engine. I would raher not do that if there is nor cause to. I just hate to throw te money and time for something that really isn't a problem.

HELP!!!

[Dunamis]

I got this from another forum. Any input:

"this is most likely a problem with the crankshaft main bearings. general motors had a bulletin on this when these engines were new and the fix was to measure the main bearings and install oversized bearings on the mains. they also note that this will not affect the longevity of the engine. bottom line is leave it alone."

[Dacaprice]

Don't feel like your alone, this is a very common issue with most years of the c/k silverado and i have yet to actually know what it is. It will be interesting to see what you end up getting done to it that fixes it.

[Ol'Jim]

Absolutely nothing to worry about, guys.
When GM added the engine oil cooler to the C/K trucks (1989 or 90), it added about 5 feet of tubing that the oil pump has to pressurize before oil gets to the main bearings. What you are hearing is a deep knock, right? (About 3 or 4 knocks then silence)... Main bearings with temporary lack of oil pressure.
You can minimize it by using 5W30 weight engine oil, (preferably Valvoline). Switch to a heavier oil, even 10/30, and it gets worse. Stay with 5/30, just like GM says, and change your oil (and filter, ALWAYS), every 2500-3000 miles. Do this and you may never hear that sound again. Very common on 90 & newer trucks, Fords do it too, but their computer immediately brings the engine to a fast idle for a second, to speed the oil pump up. You still hear them, but it's many lighter knocks, instead of a few heavy ones like the GM's. Also, wait too long between oil changes, and your oil thickens up, which makes it start the knocking thing again. I just hit 150,000 miles on my 95, and it did that for years when I was using 10/30 oil (because I was towing heavy loads and wanted the higher pressure the heavier oil gives you). Switched back to 5/30 during each Winter and last summer when I stopped towing with this truck, and no more knocking. My 1990 was sold with 293,000 miles on it, same deal. Pulled a 10,000 # trailer with both.
Relax, there is nothing wrong with your truck! Enjoy the coming Summer, and change your oil!

[Dunamis]

......

[blazes9395]

This is your mains. I know exactly what your talking about, and is common and nothing really to worry about. Its like a deep thuding noise, two or three times or so, until pressure builds and its gone. The clearences on the mains are becoming a little looser and when you first start it up, the crank is a little loose until oil pressure builds and fills the gap. Have your intake gaskets ever been replaced, no leaks etc? Whats the current milage?

What type of oil filter are you using? Avoid cheap oil filters. They are poorly constructed, and can cause engines to develop start-up noises as a result of poor drain-back valves etc. Fram is cheap, use to be good, but now is made very poorly. The good old AC delco, A Wix(Napa Gold filter), are examples of excellent filters. I wouldn't use 10-40, 10-30 is alright. High milage oils such as Valvoline Maxlife, or Castrol High Milage oils help reduce these noises and are excellent oils. I prefer and use Valvoline Maxlife. Helps with the leaks too. I don't use and wouldn't reccommend stuff like STP. Good engine oils have what your engine needs.

The difference between the 5W30/10W30/10W40 is viscosity(thickness) when cold , with the exception of the 10W40, as it acts like a 40weight oil when warm. This is a general remark, and theres more to oils, but for the sake of time(and me typing) thats what it is. The lower the weight when cold(small number), the faster it will get into your engine, protecting your engine. I myself use 0W30 in my truck, I want the oil to quickly get into the engine, reduce startup wear. I also use a little GM Oil supplement sometimes, as I have had a lot of success with it in many vehicles.
Use a good oil filter and stick with good quality oils and don't thicken it up to much, no need, plus your gas milage suffers as you use thicker oils. The noise is common, just make sure you check and make sure you have no intake leaks etc.