The Stovebolt Site Forums The Shop Area Engine Shop Rod knock???

I have what sounds like a rod knock but only for a few seconds and only when first started in the morning. This is a Chevy V8 in a later model truck. I hear a lot of "OH they do that" but I'm concerned. The truck runs great, does not use oil and oil pressure stays right around 60.
Should I pull the pan off and check or just drive it?
Any thoughts would be welcomed.
Jim

Did it happen only once? If it is rod knock it is usually consistent at certain rpms. I had rod knock at 1200 rpms but would disappear at other RPM's. I got a new motor. If it continues to happen when starting or gets louder, then you certainly have a problem. If it happened once I wouldn't be too concerned.

It could be a bad lifter it may be bleeding down overnight and in the mourning it will pump it self back up as soon as you start it .

Pete

Sounds like piston slap, very common on later model GM pickups. Go to www.pistonslap.com for a complete explanation. If that's your noise, it is considered normal.

John

Jim,

My two cents.....if the sound you actually hear is the hollow rapping of a bad connecting rod then you should be able to recreate that sound at will my manipulating engine RPM.

Some of the later Vortec engines (like mine) did have issues and could make noise. The only way a rod would knock would be from excessive clearance or maybe lack of oil.

If it truly is a rod knocking it will probably get worse. There are other accessories that can mimic this sound strangely enough...AC compressors and alternators for example. I have heard of loose or cracked flexplates on auto trannys sounding this way too!

As they say, 'it will develop'..keep us posted and good luck.

Stuart

My guess would be lifter or wrist pin or piston slap in that order. A knocking rod wouldn't disappear that quick. A knocking rod will usually get louder on deceleration or coasting down a hill.

Jim,

My 02 Silverado developed piston slap at about 70K. It was only noticable in the winter, not in the summer. For the last 20K, I now have just over 100K, it needs to be warmed up in all weather, if it has sat for several hours.

I let it warm up for a couple of minutes and it is fine. It sure is noisy at first start up in the morning.

Wow, thanks for all the response, this is an '02 Silverado also, 4.8L. This noise goes away after about a minute after start up and does not return until it sits for a couple hours. Once the noise quits, she is nice and quiet and it does not make noise again until next day. And I cannot make this noise come back at higher RPM.
Wouldn't a piston slap continue and not stop after a minute???
Somethings is bleeding down, lifter or bearing etc. The few folks I've questioned, pretty much agree that it's common and to just drive the truck. I'm thinking I may be able to fix the thing if I can narrow it down.
Thanks

A rod knock has a hard metallic ring to it. They can usually be demonstrated by giving it a tap on the gas pedal. As the RPM peaks and the rod goes off load, it will rattle if it has a problem. Some motors will exhibit a rod knock on start up until pressure is established. Sometimes this is noticeable after a new empty oil filter has been installed.

Main bearings, I've only heard in a couple of tired old motors that I have had. It was my Dad that told me what it was. Since he started work in a gas station at 9 years old. I figured he was right. It's a low thump, thump, not like a rod knock. I wouldn't think an 02 would be doing it, unless there many many miles on it.

Is the oil pressure up?

Larry

You may not believe this and some may even say im full of Bovine Excrement but I have had this issue occur with some aftermarket oil filters on Chevy V-8's. Try a AC Delco filter if you are not already using one. What you hear is the clearance between the rod bearing and the crankshaft until the oil film fills the space. A lot of newer Chevys make that noise and the dreaded piston slap as well. It seems to me car manufacturers anymore are making engines on the loose side for better fuel economy.

I'm also wondering if using a different oil would take care of this. Now using Valvoline Max Life 'blend'.

I believe that oil reaches the rod and crank bearings within 1-2 seconds after starting.

Jim,
I had a 2000 silverado that had that noise, just about made me NUTS!! Returned to dealer three/four times and was told that was a normal noise till it warmed up. Drove it 120,000 miles and never touched it.

I had a 01 GMC with the 8.1 strongest running truck I,ve ever had. Made that noise from the day I owned it till it was traded off at 100k. Guy I sold it to is still driving it no issues.

I have an 03. Same thing with 123K.