Slight knock when cold?

[PettyBlue340]

My roadrunners 340 has developed a slight knock when cold then goes away after it warms up?
This isn't too big of a surprise do to the cars originality as the motor has never been out.

Should I stop driving it or run it till I get a new short block?

This is my que to get a muscle motors 340 stroker crate short block I've been eyeing however would like to drive it while awaiting funds and build time..

 

[ArtH]

There are several types of knocking noises, rod knock, lifters are the most common. It may be a lifter that is bleeding down when the engine is off. When you first start up it's noisy until oil pressure builds up. A rod knock usually is constant and comes from the bottom of the engine. If it's that, it's a real problem. Then is could be a sloppy/loose wrist pin. Those sometimes sound like a machine gun firing. Those can be weird because sometimes they are noisy sometimes they aren't. It kind of sounds like a lifter is fixing to fail. If it is a lifter, those are too hard to replace.

But, if you have the money, maybe it's time to get that engine you appear to want and at least have it ready.

 

[rev.ronnie]

It sounds like piston slap. It will vary a little with rpm and sounds like a hollow thud.. A rocker or lifter would be a audiable "click" sound.

If it were a rod or bearing related problem, it would get worse as the oil heats up and gets thinner.

Try running a little thicker oil and see if it changes. I don't know that I'd worry a ton as long as you take it easy on it till its warmed up. There are hundreds of thousands of GM vehicles that suffer the same fate and run long lives....I have on of them!

I wouldn't buy a crate motor...find a reputable, local engine shop and build yourself a nice engine, designed for your application. A nice set of KB pistons, Edelbrock heads, adjustable valve train, a cam that suits your driving needs and a intake/carb to match and you will have a great 425 HP package that makes 400+ pounds of torque.

Find a good shop that can index and properly machine your block, balance the assembly, recondition the rods with good bolts and blueprint the Edelbrock heads and you will have a stout, reliable engine.

Crate motors are built to fit every application, a custom built engine is designed to fit YOUR application.

 

[PettyBlue340]

It sounds like piston slap. It will vary a little with rpm and sounds like a hollow thud.. A rocker or lifter would be a audiable "click" sound.

If it were a rod or bearing related problem, it would get worse as the oil heats up and gets thinner.

Try running a little thicker oil and see if it changes. I don't know that I'd worry a ton as long as you take it easy on it till its warmed up. There are hundreds of thousands of GM vehicles that suffer the same fate and run long lives....I have on of them!

I wouldn't buy a crate motor...find a reputable, local engine shop and build yourself a nice engine, designed for your application. A nice set of KB pistons, Edelbrock heads, adjustable valve train, a cam that suits your driving needs and a intake/carb to match and you will have a great 425 HP package that makes 400+ pounds of torque.

Find a good shop that can index and properly machine your block, balance the assembly, recondition the rods with good bolts and blueprint the Edelbrock heads and you will have a stout, reliable engine.

Crate motors are built to fit every application, a custom built engine is designed to fit YOUR application.

This sounds like my problem..
Yeah I already have eddy heads on the shelf and a eddy performer rpm and street demon on the car ready for a nice short block. That power range is exactly what I'm shooting for.
As far as crate motors I tend to agree but muscle motors only deals with mopars and they are built to order. Plus they have a great reputation and the price is right around 3k for complete stroker short block...

 

[RustyRatRod]

Does it sound like one knock or multiple knocks? Like a diesel maybe? If it sounds similar to a diesel until it gets warm, it's probably some piston slap. Run hell outta it.

 

[Sixer]

Yup, collapsed skirt's my guess, though a pin bore mighta gotten big.

 

[RustyRatRod]

If it's one knock, maybe a collapsed skirt. I seriously doubt all eight would crack at the same time. Seems far fetched. The knock would also continue when warmed up, too. Sounds like a little wear, to me. Besides, all modern pistons are cam ground anyway. High performance pistons even moreso. So, some cold noise in some cases is perfectly normal. Regardless, it's impossible to know since we're just armchairin it anyhow.

 

[69Bee]

XX2 = piston slap more than likely.

A piston pin should be a double knock, and a rod bearing is usually a single knock. Lifters will give a clicking noise, and I have heard that mains will growl.

Anyway, if it goes away when warm, my money is on the piston. Either it is just too worn, or a skirt has collapsed.

 

[MCODECUDA]

I had a car that had a knock just as you would start it up. It was an automatic and it turned out that the torque converter bolts loosened up.

 

[PettyBlue340]

I'm not sure if I mentioned it but it runs like a top once warm and has a lot of pull still when you floor it so I am leaning towards piston slap

 

[383man]

Definetly sounds like normal piston slap from normal wear. Heck many race engines have piston slap even when brand new since many run alot of piston to wall clearence. It all depends on the type of piston used but I would not worry about it as many cars have piston slap for years. As long as it goes away after it warms up I would say it sounds like normal wear. Ron